draft-ietf-bess-evpn-df-election-framework-06.txt   draft-ietf-bess-evpn-df-election-framework-07.txt 
skipping to change at page 1, line 14 skipping to change at page 1, line 14
Internet Draft Nokia Internet Draft Nokia
S. Mohanty, Ed. S. Mohanty, Ed.
Intended status: Standards Track A. Sajassi Intended status: Standards Track A. Sajassi
Cisco Cisco
J. Drake J. Drake
Juniper Juniper
K. Nagaraj K. Nagaraj
S. Sathappan S. Sathappan
Nokia Nokia
Expires: June 7, 2019 December 4, 2018 Expires: June 23, 2019 December 20, 2018
Framework for EVPN Designated Forwarder Election Extensibility Framework for EVPN Designated Forwarder Election Extensibility
draft-ietf-bess-evpn-df-election-framework-06 draft-ietf-bess-evpn-df-election-framework-07
Abstract Abstract
The Designated Forwarder (DF) in EVPN networks is the Provider Edge An alternative to the Default Designated Forwarder (DF) selection
(PE) router responsible for sending broadcast, unknown unicast and algorithm in Ethernet VPN (EVPN) networks is defined. The DF is the
multicast (BUM) traffic to a multi-homed Customer Equipment (CE) Provider Edge (PE) router responsible for sending broadcast, unknown
device, on a given VLAN on a particular Ethernet Segment (ES). The DF unicast and multicast (BUM) traffic to multi-homed Customer Equipment
is selected out of a list of candidate PEs that advertise the same (CE) on a particular Ethernet Segment (ES) within a VLAN. In
Ethernet Segment Identifier (ESI) to the EVPN network. By default, addition, the capability to influence the DF election result for a
EVPN uses a DF Election algorithm referred to as "Service Carving" VLAN based on the state of the associated Attachment Circuit (AC) is
and it is based on a modulus function (V mod N) that takes the number specified.
of PEs in the ES (N) and the VLAN value (V) as input. This default DF
Election algorithm has some inefficiencies that this document
addresses by defining a new DF Election algorithm and a capability to
influence the DF Election result for a VLAN, depending on the state
of the associated Attachment Circuit (AC). In addition, this document
creates a registry with IANA, for future DF Election Algorithms and
Capabilities. It also presents a formal definition and clarification
of the DF Election Finite State Machine.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents Table of Contents
1. Conventions and Terminology . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Default Designated Forwarder (DF) Election in EVPN . . . . 3
2.1. Default Designated Forwarder (DF) Election in EVPN . . . . 4 1.2. Problem Statement . . . . . . . . . . . . . . . . . . . . . 5
2.2. Problem Statement . . . . . . . . . . . . . . . . . . . . . 5 1.2.1. Unfair Load-Balancing and Service Disruption . . . . . 6
2.2.1. Unfair Load-Balancing and Service Disruption . . . . . 6 1.2.2. Traffic Black-Holing on Individual AC Failures . . . . 7
2.2.2. Traffic Black-Holing on Individual AC Failures . . . . 7 1.3. The Need for Extending the Default DF Election in EVPN . . 9
2.3. The Need for Extending the Default DF Election in EVPN . . 9 2. Conventions and Terminology . . . . . . . . . . . . . . . . . . 10
3. Designated Forwarder Election Protocol and BGP Extensions . . . 10 3. Designated Forwarder Election Protocol and BGP Extensions . . . 11
3.1 The DF Election Finite State Machine (FSM) . . . . . . . . . 10 3.1. The DF Election Finite State Machine (FSM) . . . . . . . . 12
3.2 The DF Election Extended Community . . . . . . . . . . . . . 13 3.2. The DF Election Extended Community . . . . . . . . . . . . 14
3.3 Auto-Derivation of ES-Import Route Target . . . . . . . . . 15 3.2.1. Backward Compatibility . . . . . . . . . . . . . . . . 17
4. The Highest Random Weight DF Election Type . . . . . . . . . . 15 3.3. Auto-Derivation of ES-Import Route Target . . . . . . . . . 17
4.1. HRW and Consistent Hashing . . . . . . . . . . . . . . . . 16 4. The Highest Random Weight DF Election Algorithm . . . . . . . . 17
4.2. HRW Algorithm for EVPN DF Election . . . . . . . . . . . . 16 4.1. HRW and Consistent Hashing . . . . . . . . . . . . . . . . 18
5. The Attachment Circuit Influenced DF Election Capability . . . 17 4.2. HRW Algorithm for EVPN DF Election . . . . . . . . . . . . 18
5. The Attachment Circuit Influenced DF Election Capability . . . 20
5.1. AC-Influenced DF Election Capability For VLAN-Aware 5.1. AC-Influenced DF Election Capability For VLAN-Aware
Bundle Services . . . . . . . . . . . . . . . . . . . . . . 19 Bundle Services . . . . . . . . . . . . . . . . . . . . . . 22
6. Solution Benefits . . . . . . . . . . . . . . . . . . . . . . . 20 6. Solution Benefits . . . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 21 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 21 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.1. Normative References . . . . . . . . . . . . . . . . . . . 21 9.1. Normative References . . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . . 22 9.2. Informative References . . . . . . . . . . . . . . . . . . 25
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
1. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
o AC and ACS - Attachment Circuit and Attachment Circuit Status. An
AC has an Ethernet Tag associated to it.
o BUM - refers to the Broadcast, Unknown unicast and Multicast
traffic.
o DF, NDF and BDF - Designated Forwarder, Non-Designated Forwarder
and Backup Designated Forwarder
o Ethernet A-D per ES route - refers to [RFC7432] route type 1 or
Auto-Discovery per Ethernet Segment route.
o Ethernet A-D per EVI route - refers to [RFC7432] route type 1 or
Auto-Discovery per EVPN Instance route.
o ES and ESI - Ethernet Segment and Ethernet Segment Identifier.
o EVI - EVPN Instance.
o BD - Broadcast Domain. An EVI may be comprised of one (VLAN-Based
or VLAN-Bundle services) or multiple (VLAN-Aware Bundle services)
Broadcast Domains.
o HRW - Highest Random Weight
o VID and CE-VID - VLAN Identifier and Customer Equipment VLAN
Identifier.
o Ethernet Tag - used to represent a Broadcast Domain that is
configured on a given ES for the purpose of DF election. Note that
any of the following may be used to represent a Broadcast Domain:
VIDs (including double Q-in-Q tags), configured IDs, VNI,
normalized VID, I-SIDs, etc., as long as the representation of the
broadcast domains is configured consistently across the multi-homed
PEs attached to that ES. The Ethernet Tag value MUST be different
from zero.
o Ethernet Tag ID - refers to the identifier used in the EVPN routes
defined in [RFC7432]. Its value may be the same as the Ethernet Tag
value (see Ethernet Tag definition) when advertising routes for
VLAN-aware bundle services. Note that in case of VLAN-based or VLAN
Bundle services, the Ethernet Tag ID is zero.
o DF Election Procedure and DF Algorithm - The Designated Forwarder 1. Introduction
Election Procedure or simply DF Election, refers to the process in
its entirety, including the discovery of the PEs in the ES, the
creation and maintenance of the PE candidate list and the selection
of a PE. The Designated Forwarder Algorithm is just a component of
the DF Election Procedure and strictly refers to the selection of a
PE for a given <ES,Ethernet Tag>.
This document also assumes familiarity with the terminology of The Designated Forwarder (DF) in EVPN networks is the Provider Edge
[RFC7432]. (PE) router responsible for sending broadcast, unknown unicast and
multicast (BUM) traffic to a multi-homed Customer Equipment (CE)
device, on a given VLAN on a particular Ethernet Segment (ES). The DF
is selected out of a list of candidate PEs that advertise the same
Ethernet Segment Identifier (ESI) to the EVPN network. By default,
EVPN uses a DF Election algorithm referred to as "Service Carving"
and it is based on a modulus function (V mod N) that takes the number
of PEs in the ES (N) and the VLAN value (V) as input. This Default DF
Election algorithm has some inefficiencies that this document
addresses by defining a new DF Election algorithm and a capability to
influence the DF Election result for a VLAN, depending on the state
of the associated Attachment Circuit (AC). In order to avoid any
ambiguity with the identifier used in the DF Election Algorithm, this
document uses the term Ethernet Tag instead of VLAN. This document
also creates a registry with IANA, for future DF Election Algorithms
and Capabilities. It also presents a formal definition and
clarification of the DF Election Finite State Machine.
2. Introduction The procedures described in this document apply to [RFC7432] and
[RFC8214] EVPN networks. This document does not intend to update
[RFC7432] or [RFC8214] but intends to improve the behavior of the DF
Election on PEs that are upgraded to follow the described procedures.
2.1. Default Designated Forwarder (DF) Election in EVPN 1.1. Default Designated Forwarder (DF) Election in EVPN
[RFC7432] defines the Designated Forwarder (DF) as the EVPN PE [RFC7432] defines the Designated Forwarder (DF) as the EVPN PE
responsible for: responsible for:
o Flooding Broadcast, Unknown unicast and Multicast traffic (BUM), on o Flooding Broadcast, Unknown unicast and Multicast traffic (BUM), on
a given Ethernet Tag on a particular Ethernet Segment (ES), to the a given Ethernet Tag on a particular Ethernet Segment (ES), to the
CE. This is valid for single-active and all-active EVPN CE. This is valid for single-active and all-active EVPN
multi-homing. multi-homing.
o Sending unicast traffic on a given Ethernet Tag on a particular ES o Sending unicast traffic on a given Ethernet Tag on a particular ES
to the CE. This is valid for single-active multi-homing. to the CE. This is valid for single-active multi-homing.
Figure 1 illustrates an example that we will use to explain the Figure 1 illustrates an example that we will use to explain the
Designated Forwarder function. Designated Forwarder function.
+---------------+ +---------------+
| IP/MPLS | | IP/MPLS |
| CORE | | CORE |
+----+ ES1 +----+ +----+ +----+ ES1 +----+ +----+
| CE1|-----| |-----------| |____ES2 | CE1|-----| | | |____ES2
+----+ | PE1| | PE2| \ +----+ | PE1| | PE2| \
| |-------- +----+ \+----+ | | +----+ \+----+
+----+ | | | CE2| +----+ | | CE2|
| | +----+ /+----+ | +----+ /+----+
| |__| |____/ | | | |____/ |
| | PE3| ES2 / | | PE3| ES2 /
| +----+ / | +----+ /
| | / | | /
+-------------+----+ / +-------------+----+ /
| PE4|____/ES2 | PE4|____/ES2
| | | |
+----+ +----+
Figure 1 Multi-homing Network of EVPN Figure 1 Multi-homing Network of EVPN
Figure 1 illustrates a case where there are two Ethernet Segments, Figure 1 illustrates a case where there are two Ethernet Segments,
ES1 and ES2. PE1 is attached to CE1 via Ethernet Segment ES1 whereas ES1 and ES2. PE1 is attached to CE1 via Ethernet Segment ES1 whereas
PE2, PE3 and PE4 are attached to CE2 via ES2 i.e. PE2, PE3 and PE4 PE2, PE3 and PE4 are attached to CE2 via ES2 i.e. PE2, PE3 and PE4
form a redundancy group. Since CE2 is multi-homed to different PEs on form a redundancy group. Since CE2 is multi-homed to different PEs on
the same Ethernet Segment, it is necessary for PE2, PE3 and PE4 to the same Ethernet Segment, it is necessary for PE2, PE3 and PE4 to
agree on a DF to satisfy the above mentioned requirements. agree on a DF to satisfy the above mentioned requirements.
Layer-2 devices are particularly susceptible to forwarding loops The effect of forwarding loops in a Layer-2 network is particularly
because of the broadcast nature of the Ethernet traffic. Therefore it severe because of the broadcast nature of Ethernet traffic and the
is very important that, in case of multi-homing, only one of the lack of a Time-To-Live (TTL). Therefore it is very important that in
links be used to direct traffic to/from the core. the case of a multi-homed CE only one of the PEs be used to send BUM
traffic to it.
One of the pre-requisites for this support is that participating PEs One of the pre-requisites for this support is that participating PEs
must agree amongst themselves as to who would act as the Designated must agree amongst themselves as to who would act as the Designated
Forwarder (DF). This needs to be achieved through a distributed Forwarder (DF). This needs to be achieved through a distributed
algorithm in which each participating PE independently and algorithm in which each participating PE independently and
unambiguously selects one of the participating PEs as the DF, and the unambiguously selects one of the participating PEs as the DF, and the
result should be consistent and unanimous. result should be consistent and unanimous.
The default algorithm for DF election defined by [RFC7432] at the The default algorithm for DF election defined by [RFC7432] at the
granularity of (ESI,EVI) is referred to as "service carving". In this granularity of (ESI,EVI) is referred to as "service carving". In this
document, service carving or default DF Election algorithm are used document, service carving and Default DF Election algorithm are used
interchangeably. With service carving, it is possible to elect interchangeably. With service carving, it is possible to elect
multiple DFs per Ethernet Segment (one per EVI) in order to perform multiple DFs per Ethernet Segment (one per EVI) in order to perform
load-balancing of traffic destined to a given Segment. The objective load-balancing of traffic destined to a given Segment. The objective
is that the load-balancing procedures should carve up the BD space is that the load-balancing procedures should carve up the BD space
among the redundant PE nodes evenly, in such a way that every PE is among the redundant PE nodes evenly, in such a way that every PE is
the DF for a distinct set of EVIs. the DF for a distinct set of EVIs.
The DF Election algorithm as described in [RFC7432] (Section 8.5) is The DF Election algorithm as described in [RFC7432] (Section 8.5) is
based on a modulus operation. The PEs to which the ES (for which DF based on a modulus operation. The PEs to which the ES (for which DF
election is to be carried out per EVI) is multi-homed form an ordered election is to be carried out per EVI) is multi-homed form an ordered
(ordinal) list in ascending order of the PE IP address values. For (ordinal) list in ascending order of the PE IP address values. For
example, there are N PEs: PE0, PE1,... PEN-1 ranked as per increasing example, there are N PEs: PE0, PE1,... PEN-1 ranked as per increasing
IP addresses in the ordinal list; then for each VLAN with Ethernet IP addresses in the ordinal list; then for each VLAN with Ethernet
Tag V, configured on the Ethernet Segment ES1, PEx is the DF for VLAN Tag V, configured on the Ethernet Segment ES1, PEx is the DF for VLAN
V on ES1 when x equals (V mod N). In the case of VLAN-Bundle only the V on ES1 when x equals (V mod N). In the case of VLAN Bundle only the
lowest VLAN is used. In the case when the planned density is high lowest VLAN is used. In the case when the planned density is high
(meaning there are significant number of VLANs and the Ethernet Tags (meaning there are significant number of VLANs and the Ethernet Tags
are uniformly distributed), the thinking is that the DF Election will are uniformly distributed), the thinking is that the DF Election will
be spread across the PEs hosting that Ethernet Segment and good load- be spread across the PEs hosting that Ethernet Segment and good load-
balancing can be achieved. balancing can be achieved.
However, the described default DF Election algorithm has some However, the described Default DF Election algorithm has some
undesirable properties and in some cases can be somewhat disruptive undesirable properties and in some cases can be somewhat disruptive
and unfair. This document describes some of those issues and proposes and unfair. This document describes some of those issues and defines
a mechanism for dealing with them. These mechanisms do involve a mechanism for dealing with them. These mechanisms do involve
changes to the default DF Election algorithm, but they do not require changes to the Default DF Election algorithm, but they do not require
any changes to the EVPN Route exchange and have minimal changes to any changes to the EVPN Route exchange and have minimal changes in
their content per se. the EVPN routes.
In addition, there is a need to extend the DF Election procedures so In addition, there is a need to extend the DF Election procedures so
that new algorithms and capabilities are possible. A single algorithm that new algorithms and capabilities are possible. A single algorithm
(the default DF Election algorithm) may not meet the requirements in (the Default DF Election algorithm) may not meet the requirements in
all the use-cases. all the use-cases.
Note that while [RFC7432] elects a DF per <ES, EVI>, this document Note that while [RFC7432] elects a DF per <ES, EVI>, this document
elects a DF per <ES, BD>. This means that unlike [RFC7432], where for elects a DF per <ES, BD>. This means that unlike [RFC7432], where for
a VLAN Aware Bundle service EVI there is only one DF for the EVI, a VLAN-Aware Bundle service EVI there is only one DF for the EVI,
this document specifies that there will be multiple DFs, one for each this document specifies that there will be multiple DFs, one for each
BD configured in that EVI. BD configured in that EVI.
2.2. Problem Statement 1.2. Problem Statement
This section describes some potential issues with the default DF This section describes some potential issues with the Default DF
Election algorithm. Election algorithm.
2.2.1. Unfair Load-Balancing and Service Disruption 1.2.1. Unfair Load-Balancing and Service Disruption
There are three fundamental problems with the current default DF There are three fundamental problems with the current Default DF
Election algorithm. Election algorithm.
1- First, the algorithm will not perform well when the Ethernet Tag 1- First, the algorithm will not perform well when the Ethernet Tag
follows a non-uniform distribution, for instance when the Ethernet follows a non-uniform distribution, for instance when the Ethernet
Tags are all even or all odd. In such a case let us assume that Tags are all even or all odd. In such a case let us assume that
the ES is multi-homed to two PEs; one of the PEs will be elected the ES is multi-homed to two PEs; one of the PEs will be elected
as DF for all of the VLANs. This is very sub-optimal. It defeats as DF for all of the VLANs. This is very sub-optimal. It defeats
the purpose of service carving as the DFs are not really evenly the purpose of service carving as the DFs are not really evenly
spread across. In fact, in this particular case, one of the PEs spread across. In fact, in this particular case, one of the PEs
does not get elected as DF at all, so it does not participate in does not get elected as DF at all, so it does not participate in
skipping to change at page 7, line 36 skipping to change at page 6, line 31
is associated with an Ethernet Tag of the form (3x+1), where x is is associated with an Ethernet Tag of the form (3x+1), where x is
an integer. This will result in PE3 always be selected as the DF. an integer. This will result in PE3 always be selected as the DF.
2- Even in the case when the Ethernet Tag distribution is uniform the 2- Even in the case when the Ethernet Tag distribution is uniform the
instance of a PE being up or down results in re-computation ((v instance of a PE being up or down results in re-computation ((v
mod N-1) or (v mod N+1) as is the case); the resulting modulus mod N-1) or (v mod N+1) as is the case); the resulting modulus
value need not be uniformly distributed because it can be subject value need not be uniformly distributed because it can be subject
to the primality of N-1 or N+1 as may be the case. to the primality of N-1 or N+1 as may be the case.
3- The third problem is one of disruption. Consider a case when the 3- The third problem is one of disruption. Consider a case when the
same Ethernet Segment is multi homed to a set of PEs. When the ES same Ethernet Segment is multi-homed to a set of PEs. When the ES
is down in one of the PEs, say PE1, or PE1 itself reboots, or the is down in one of the PEs, say PE1, or PE1 itself reboots, or the
BGP process goes down or the connectivity between PE1 and an RR BGP process goes down or the connectivity between PE1 and an RR
goes down, the effective number of PEs in the system now becomes goes down, the effective number of PEs in the system now becomes
N-1, and DFs are computed for all the VLANs that are configured on N-1, and DFs are computed for all the VLANs that are configured on
that Ethernet Segment. In general, if the DF for a VLAN v happens that Ethernet Segment. In general, if the DF for a VLAN v happens
not to be PE1, but some other PE, say PE2, it is likely that some not to be PE1, but some other PE, say PE2, it is likely that some
other PE will become the new DF. This is not desirable. Similarly other PE (different from PE1 and PE2) will become the new DF. This
when a new PE hosts the same Ethernet Segment, the mapping again is not desirable. Similarly when a new PE hosts the same Ethernet
changes because of the modulus operation. This results in needless Segment, the mapping again changes because of the modulus
churn. Again referring to Figure 1, say v1, v2 and v3 are VLANs operation. This results in needless churn. Again referring to
configured on ES2 with associated Ethernet Tags of value 999, 1000 Figure 1, say v1, v2 and v3 are VLANs configured on ES2 with
and 1001 respectively. So PE1, PE2 and PE3 are the DFs for v1, v2 associated Ethernet Tags of value 999, 1000 and 1001 respectively.
and v3 respectively. Now when PE3 goes down, PE2 will become the So PE1, PE2 and PE3 are the DFs for v1, v2 and v3 respectively.
DF for v1 and PE1 will become the DF for v2. Now when PE3 goes down, PE2 will become the DF for v1 and PE1 will
become the DF for v2.
One point to note is that the default DF election algorithm assumes One point to note is that the Default DF election algorithm assumes
that all the PEs who are multi-homed to the same Ethernet Segment that all the PEs who are multi-homed to the same Ethernet Segment
(and interested in the DF Election by exchanging EVPN routes) use an (and interested in the DF Election by exchanging EVPN routes) use an
Originating Router's IP Address of the same family. This does not Originating Router's IP Address of the same family. This does not
need to be the case as the EVPN address-family can be carried over a need to be the case as the EVPN address-family can be carried over an
v4 or v6 peering, and the PEs attached to the same ES may use an IPv4 or IPv6 peering, and the PEs attached to the same ES may use an
address of either family. address of either family.
Mathematically, a conventional hash function maps a key k to a number Mathematically, a conventional hash function maps a key k to a number
i representing one of m hash buckets through a function h(k) i.e. i representing one of m hash buckets through a function h(k) i.e.
i=h(k). In the EVPN case, h is simply a modulo-m hash function viz. i=h(k). In the EVPN case, h is simply a modulo-m hash function viz.
h(v) = v mod N, where N is the number of PEs that are multi-homed to h(v) = v mod N, where N is the number of PEs that are multi-homed to
the Ethernet Segment in discussion. It is well-known that for good the Ethernet Segment in discussion. It is well-known that for good
hash distribution using the modulus operation, the modulus N should hash distribution using the modulus operation, the modulus N should
be a prime-number not too close to a power of 2 [CLRS2009]. When the be a prime-number not too close to a power of 2 [CLRS2009]. When the
effective number of PEs changes from N to N-1 (or vice versa); all effective number of PEs changes from N to N-1 (or vice versa); all
the objects (VLAN V) will be remapped except those for which V mod N the objects (VLAN V) will be remapped except those for which V mod N
and V mod (N-1) refer to the same PE in the previous and subsequent and V mod (N-1) refer to the same PE in the previous and subsequent
ordinal rankings respectively. From a forwarding perspective, this is ordinal rankings respectively. From a forwarding perspective, this is
a churn, as it results in re-programming the PE ports as either a churn, as it results in re-programming the PE ports as either
blocking or non-blocking at potentially all PEs when the DF changes. blocking or non-blocking at the PEs where the DF state changes.
This document addresses this problem and furnishes a solution to this This document addresses this problem and furnishes a solution to this
undesirable behavior. undesirable behavior.
2.2.2. Traffic Black-Holing on Individual AC Failures 1.2.2. Traffic Black-Holing on Individual AC Failures
As discussed in section 2.1 the default DF Election algorithm defined As discussed in section 2.1 the Default DF Election algorithm defined
by [RFC7432] takes into account only two variables in the modulus by [RFC7432] takes into account only two variables in the modulus
function for a given ES: the existence of the PE's IP address on the function for a given ES: the existence of the PE's IP address on the
candidate list and the locally provisioned Ethernet Tags. candidate list and the locally provisioned Ethernet Tags.
If the DF for an <ESI, EVI> fails (due to physical link/node If the DF for an <ESI, EVI> fails (due to physical link/node
failures) an ES route withdrawal will make the Non-DF (NDF) PEs re- failures) an ES route withdrawal will make the Non-DF (NDF) PEs re-
elect the DF for that <ESI, EVI> and the service will be recovered. elect the DF for that <ESI, EVI> and the service will be recovered.
However, the default DF election procedure does not provide a However, the Default DF election procedure does not provide a
protection against "logical" failures or human errors that may occur protection against "logical" failures or human errors that may occur
at service level on the DF, while the list of active PEs for a given at service level on the DF, while the list of active PEs for a given
ES does not change. These failures may have an impact not only on the ES does not change. These failures may have an impact not only on the
local PE where the issue happens, but also on the rest of the PEs of local PE where the issue happens, but also on the rest of the PEs of
the ES. Some examples of such logical failures are listed below: the ES. Some examples of such logical failures are listed below:
a) A given individual Attachment Circuit (AC) defined in an ES is a) A given individual Attachment Circuit (AC) defined in an ES is
accidentally shutdown or even not provisioned yet (hence the accidentally shutdown or even not provisioned yet (hence the
Attachment Circuit Status - ACS - is DOWN), while the ES is Attachment Circuit Status - ACS - is DOWN), while the ES is
operationally active (since the ES route is active). operationally active (since the ES route is active).
skipping to change at page 10, line 7 skipping to change at page 8, line 50
BD-1 is defined in PE1, PE2, PE3 and PE4. CE12 is a multi-homed CE BD-1 is defined in PE1, PE2, PE3 and PE4. CE12 is a multi-homed CE
connected to ES12 in PE1 and PE2. Similarly CE23 is multi-homed to connected to ES12 in PE1 and PE2. Similarly CE23 is multi-homed to
PE2 and PE3 using ES23. Both, CE12 and CE23, are connected to BD-1 PE2 and PE3 using ES23. Both, CE12 and CE23, are connected to BD-1
through VLAN-based service interfaces: CE12-VID 1 (VLAN ID 1 on CE12) through VLAN-based service interfaces: CE12-VID 1 (VLAN ID 1 on CE12)
is associated to AC1 and AC2 in BD-1, whereas CE23-VID 1 is is associated to AC1 and AC2 in BD-1, whereas CE23-VID 1 is
associated to AC3 and AC4 in BD-1. Assume that, although not associated to AC3 and AC4 in BD-1. Assume that, although not
represented, there are other ACs defined on these ES mapped to represented, there are other ACs defined on these ES mapped to
different BDs. different BDs.
After running the [RFC7432] default DF election algorithm, PE2 turns After executing the [RFC7432] Default DF election algorithm, PE2
out to be the DF for ES12 and ES23 in BD-1. The following issues may turns out to be the DF for ES12 and ES23 in BD-1. The following
arise: issues may arise:
a) If AC2 is accidentally shutdown or even not configured, CE12 a) If AC2 is accidentally shutdown or even not configured, CE12
traffic will be impacted. In case of all-active multi-homing, the traffic will be impacted. In case of all-active multi-homing, the
BUM traffic to CE12 will be "black-holed", whereas for single- BUM traffic to CE12 will be "black-holed", whereas for single-
active multi-homing, all the traffic to/from CE12 will be active multi-homing, all the traffic to/from CE12 will be
discarded. This is due to the fact that a logical failure in PE2's discarded. This is due to the fact that a logical failure in PE2's
AC2 may not trigger an ES route withdrawn for ES12 (since there AC2 may not trigger an ES route withdrawn for ES12 (since there
are still other ACs active on ES12) and therefore PE1 will not re- are still other ACs active on ES12) and therefore PE1 will not re-
run the DF election procedures. run the DF election procedures.
skipping to change at page 10, line 41 skipping to change at page 9, line 36
the decommissioning", however, while this A-D per EVI route the decommissioning", however, while this A-D per EVI route
withdrawal is used at the remote PEs performing aliasing or backup withdrawal is used at the remote PEs performing aliasing or backup
procedures, it is not used to influence the DF election for the procedures, it is not used to influence the DF election for the
affected EVIs. affected EVIs.
This document adds an optional modification of the DF Election This document adds an optional modification of the DF Election
procedure so that the ACS may be taken into account as a variable in procedure so that the ACS may be taken into account as a variable in
the DF election, and therefore EVPN can provide protection against the DF election, and therefore EVPN can provide protection against
logical failures. logical failures.
2.3. The Need for Extending the Default DF Election in EVPN 1.3. The Need for Extending the Default DF Election in EVPN
Section 2.2 describes some of the issues that exist in the default DF Section 2.2 describes some of the issues that exist in the Default DF
Election procedures. In order to address those issues, this document Election procedures. In order to address those issues, this document
introduces a new DF Election framework. This framework allows the PEs introduces a new DF Election framework. This framework allows the PEs
to agree on a common DF election algorithm, as well as the to agree on a common DF election algorithm, as well as the
capabilities to enable during the DF Election procedure Generally, capabilities to enable during the DF Election procedure. Generally,
'DF election algorithm' refers to the algorithm by which a number of 'DF election algorithm' refers to the algorithm by which a number of
input parameters are used to determine the DF PE, while 'DF election input parameters are used to determine the DF PE, while 'DF election
capability' refers to an additional feature that can be used prior to capability' refers to an additional feature that can be used prior to
the invocation of the DF election algorithm, such as modifying the the invocation of the DF election algorithm, such as modifying the
inputs (or list of candidate PEs). inputs (or list of candidate PEs).
Within this framework, this document defines a new DF Election Within this framework, this document defines a new DF Election
algorithm and a new capability that can influence the DF Election algorithm and a new capability that can influence the DF Election
result: result:
o The new DF Election algorithm is referred to as "Highest Random o The new DF Election algorithm is referred to as "Highest Random
Weight" (HRW). The HRW procedures are described in section 4. Weight" (HRW). The HRW procedures are described in section 4.
o The new DF Election capability is referred to as "AC-Influenced DF o The new DF Election capability is referred to as "AC-Influenced DF
Election" (AC-DF). The AC-DF procedures are described in section 5. Election" (AC-DF). The AC-DF procedures are described in section 5.
o HRW and AC-DF mechanisms are independent of each other. Therefore, o HRW and AC-DF mechanisms are independent of each other. Therefore,
a PE MAY support either HRW or AC-DF independently or MAY support a PE MAY support either HRW or AC-DF independently or MAY support
both of them together. A PE MAY also support AC-DF capability along both of them together. A PE MAY also support AC-DF capability along
with the default DF election algorithm per [RFC7432]. with the Default DF election algorithm per [RFC7432].
In addition, this document defines a way to indicate the support of In addition, this document defines a way to indicate the support of
HRW and/or AC-DF along with the EVPN ES routes advertised for a given HRW and/or AC-DF along with the EVPN ES routes advertised for a given
ES. Refer to section 3.2 for more details. ES. Refer to section 3.2 for more details.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
o AC and ACS - Attachment Circuit and Attachment Circuit Status. An
AC has an Ethernet Tag associated to it.
o BUM - refers to the Broadcast, Unknown unicast and Multicast
traffic.
o DF, NDF and BDF - Designated Forwarder, Non-Designated Forwarder
and Backup Designated Forwarder
o Ethernet A-D per ES route - refers to [RFC7432] route type 1 or
Auto-Discovery per Ethernet Segment route.
o Ethernet A-D per EVI route - refers to [RFC7432] route type 1 or
Auto-Discovery per EVPN Instance route.
o ES and ESI - Ethernet Segment and Ethernet Segment Identifier.
o EVI - EVPN Instance.
o MAC-VRF - A Virtual Routing and Forwarding table for Media Access
Control (MAC) addresses on a PE.
o BD - Broadcast Domain. An EVI may be comprised of one (VLAN-Based
or VLAN Bundle services) or multiple (VLAN-Aware Bundle services)
Broadcast Domains.
o Bridge Table - An instantiation of a broadcast domain on a MAC-VRF.
o HRW - Highest Random Weight
o VID and CE-VID - VLAN Identifier and Customer Equipment VLAN
Identifier.
o Ethernet Tag - used to represent a Broadcast Domain that is
configured on a given ES for the purpose of DF election. Note that
any of the following may be used to represent a Broadcast Domain:
VIDs (including Q-in-Q tags), configured IDs, VNI (VXLAN Network
Identifiers), normalized VID, I-SIDs (Service Instance
Identifiers), etc., as long as the representation of the broadcast
domains is configured consistently across the multi-homed PEs
attached to that ES. The Ethernet Tag value MUST be different from
zero.
o Ethernet Tag ID - refers to the identifier used in the EVPN routes
defined in [RFC7432]. Its value may be the same as the Ethernet Tag
value (see Ethernet Tag definition) when advertising routes for
VLAN-aware Bundle services. Note that in case of VLAN-based or VLAN
Bundle services, the Ethernet Tag ID is zero.
o DF Election Procedure and DF Algorithm - The Designated Forwarder
Election Procedure or simply DF Election, refers to the process in
its entirety, including the discovery of the PEs in the ES, the
creation and maintenance of the PE candidate list and the selection
of a PE. The Designated Forwarder Algorithm is just a component of
the DF Election Procedure and strictly refers to the selection of a
PE for a given <ES,Ethernet Tag>.
o TTL - Time To Live
This document also assumes familiarity with the terminology of
[RFC7432].
3. Designated Forwarder Election Protocol and BGP Extensions 3. Designated Forwarder Election Protocol and BGP Extensions
This section describes the BGP extensions required to support the new This section describes the BGP extensions required to support the new
DF Election procedures. In addition, since the specification in EVPN DF Election procedures. In addition, since the EVPN specification
[RFC7432] does leave several questions open as to the precise final [RFC7432] does leave several questions open as to the precise final
state machine behavior of the DF election, section 3.1 describes state machine behavior of the DF election, section 3.1 describes
precisely the intended behavior. precisely the intended behavior.
3.1 The DF Election Finite State Machine (FSM) 3.1. The DF Election Finite State Machine (FSM)
Per [RFC7432], the FSM described in Figure 3 is executed per Per [RFC7432], the FSM described in Figure 3 is executed per
<ESI,VLAN> in case of VLAN-based service or <ESI,[VLANs in VLAN- <ESI,VLAN> in case of VLAN-based service or <ESI,[VLANs in VLAN
Bundle]> in case of VLAN-Bundle on each participating PE. Bundle]> in case of VLAN Bundle on each participating PE.
Observe that currently the VLANs are derived from local configuration Observe that currently the VLANs are derived from local configuration
and the FSM does not provide any protection against misconfiguration and the FSM does not provide any protection against misconfiguration
where the same (EVI,ESI) combination has different set of VLANs on where the same (EVI,ESI) combination has different set of VLANs on
different participating PEs or one of the PEs elects to consider different participating PEs or one of the PEs elects to consider
VLANs as VLAN-Bundle and another as separate VLANs for election VLANs as VLAN Bundle and another as separate VLANs for election
purposes (service type mismatch). purposes (service type mismatch).
The FSM is conceptual and any design or implementation MUST comply The FSM is conceptual and any design or implementation MUST comply
with a behavior equivalent to the one outlined in this FSM. with a behavior equivalent to the one outlined in this FSM.
VLAN_CHANGE VLAN_CHANGE
VLAN_CHANGE RCVD_ES VLAN_CHANGE RCVD_ES
RCVD_ES LOST_ES RCVD_ES LOST_ES
LOST_ES +----+ LOST_ES +----+
+----+ | v +----+ | v
skipping to change at page 12, line 35 skipping to change at page 12, line 51
VLAN_CHANGE VLAN_CHANGE
RCVD_ES RCVD_ES
LOST_ES LOST_ES
Figure 3 DF Election Finite State Machine Figure 3 DF Election Finite State Machine
States: States:
1. INIT: Initial State 1. INIT: Initial State
2. DF WAIT: State in which the participant waits for enough 2. DF_WAIT: State in which the participant waits for enough
information to perform the DF election for the EVI/ESI/VLAN information to perform the DF election for the EVI/ESI/VLAN
combination. combination.
3. DF CALC: State in which the new DF is recomputed. 3. DF_CALC: State in which the new DF is recomputed.
4. DF DONE: State in which the according DF for the EVI/ESI/VLAN 4. DF_DONE: State in which the according DF for the EVI/ESI/VLAN
combination has been elected. combination has been elected.
5. ANY_STATE: Refers to any of the above states.
Events: Events:
1. ES_UP: The ESI has been locally configured as 'up'. 1. ES_UP: The ESI has been locally configured as 'up'.
2. ES_DOWN: The ESI has been locally configured as 'down'. 2. ES_DOWN: The ESI has been locally configured as 'down'.
3. VLAN_CHANGE: The VLANs configured in a bundle (that uses the ESI) 3. VLAN_CHANGE: The VLANs configured in a bundle (that uses the ESI)
changed. This event is necessary for VLAN-Bundles only. changed. This event is necessary for VLAN Bundles only.
4. DF_TIMER: DF Wait timer has expired. 4. DF_TIMER: DF Wait timer [RFC7432] has expired.
5. RCVD_ES: A new or changed Ethernet Segment Route is received in a 5. RCVD_ES: A new or changed Ethernet Segment route is received in a
BGP REACH UPDATE. Receiving an unchanged UPDATE MUST NOT trigger BGP REACH UPDATE. Receiving an unchanged UPDATE MUST NOT trigger
this event. this event.
6. LOST_ES: A BGP UNREACH UPDATE for a previously received Ethernet 6. LOST_ES: A BGP UNREACH UPDATE for a previously received Ethernet
Segment route has been received. If an UNREACH is seen for a Segment route has been received. If an UNREACH is seen for a
route that has not been advertised previously, the event MUST NOT route that has not been advertised previously, the event MUST NOT
be triggered. be triggered.
7. CALCULATED: DF has been successfully calculated. 7. CALCULATED: DF has been successfully calculated.
According actions when transitions are performed or states According actions when transitions are performed or states
entered/exited: entered/exited:
1. ANY STATE on ES_DOWN: (i) stop DF timer (ii) assume non-DF for 1. ANY_STATE on ES_DOWN: (i) stop DF wait timer (ii) assume NDF for
local PE. local PE.
2. INIT on ES_UP: transition to DF_WAIT. 2. INIT on ES_UP: transition to DF_WAIT.
3. INIT on VLAN_CHANGE, RCVD_ES, LOST_ES: do nothing. 3. INIT on VLAN_CHANGE, RCVD_ES or LOST_ES: do nothing.
4. DF_WAIT on entering the state: (i) start DF timer if not started 4. DF_WAIT on entering the state: (i) start DF wait timer if not
already or expired (ii) assume non-DF for local PE. started already or expired (ii) assume NDF for local PE.
5. DF_WAIT on VLAN_CHANGE, RCVD_ES, LOST_ES: do nothing. 5. DF_WAIT on VLAN_CHANGE, RCVD_ES or LOST_ES: do nothing.
6. DF_WAIT on DF_TIMER: transition to DF_CALC. 6. DF_WAIT on DF_TIMER: transition to DF_CALC.
7. DF_CALC on entering or re-entering the state: (i) rebuild 7. DF_CALC on entering or re-entering the state: (i) rebuild
candidate list, hash and perform election (ii) Afterwards FSM candidate list, hash and perform election (ii) Afterwards FSM
generates CALCULATED event against itself. generates CALCULATED event against itself.
8. DF_CALC on VLAN_CHANGE, RCVD_ES, LOST_ES: do nothing. 8. DF_CALC on VLAN_CHANGE, RCVD_ES or LOST_ES: do as in transition
7.
9. DF_CALC on CALCULATED: mark election result for VLAN or bundle, 9. DF_CALC on CALCULATED: mark election result for VLAN or bundle,
and transition to DF_DONE. and transition to DF_DONE.
11. DF_DONE on exiting the state: if there is a new DF election 11. DF_DONE on exiting the state: if there is a new DF election
triggered and the current DF is lost, then assume non-DF for triggered and the current DF is lost, then assume NDF for local
local PE for VLAN or VLAN-Bundle. PE for VLAN or VLAN Bundle.
12. DF_DONE on VLAN_CHANGE, RCVD_ES or LOST_ES: transition to 12. DF_DONE on VLAN_CHANGE, RCVD_ES or LOST_ES: transition to
DF_CALC. DF_CALC.
3.2 The DF Election Extended Community 3.2. The DF Election Extended Community
For the DF election procedures to be consistent and unanimous, it is For the DF election procedures to be consistent and unanimous, it is
necessary that all the participating PEs agree on the DF Election necessary that all the participating PEs agree on the DF Election
algorithm and capabilities to be used. For instance, it is not algorithm and capabilities to be used. For instance, it is not
possible that some PEs continue to use the default DF Election possible that some PEs continue to use the Default DF Election
algorithm and some PEs use HRW. For brown-field deployments and for algorithm and some PEs use HRW. For brown-field deployments and for
interoperability with legacy PEs, it is important that all PEs need interoperability with legacy PEs, it is important that all PEs need
to have the capability to fall back on the Default DF Election. A PE to have the capability to fall back on the Default DF Election. A PE
can indicate its willingness to support HRW and/or AC-DF by signaling can indicate its willingness to support HRW and/or AC-DF by signaling
a DF Election Extended Community along with the Ethernet Segment a DF Election Extended Community along with the Ethernet Segment
Route (Type-4). route (Type-4).
The DF Election Extended Community is a new BGP transitive extended The DF Election Extended Community is a new BGP transitive extended
community attribute [RFC4360] that is defined to identify the DF community attribute [RFC4360] that is defined to identify the DF
election procedure to be used for the Ethernet Segment. Figure 4 election procedure to be used for the Ethernet Segment. Figure 4
shows the encoding of the DF Election Extended Community. shows the encoding of the DF Election Extended Community.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type(0x06)| RSV | DF Alg | Bitmap | | Type=0x06 | Sub-Type(0x06)| RSV | DF Alg | Bitmap ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap | Reserved | ~ Bitmap | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 DF Election Extended Community Figure 4 DF Election Extended Community
Where: Where:
o Type is 0x06 as registered with IANA for EVPN Extended Communities. o Type is 0x06 as registered with IANA for EVPN Extended Communities.
o Sub-Type is 0x06 - "DF Election Extended Community" as requested by o Sub-Type is 0x06 - "DF Election Extended Community" as requested by
this document to IANA. this document to IANA.
skipping to change at page 16, line 19 skipping to change at page 16, line 40
- In the case that they do, this particular PE MUST follow the - In the case that they do, this particular PE MUST follow the
procedures for the advertised DF Alg and capabilities. For procedures for the advertised DF Alg and capabilities. For
instance, if all ES routes for a given ES indicate DF Alg HRW and instance, if all ES routes for a given ES indicate DF Alg HRW and
AC-DF set to 1, the receiving PE and by induction all the other AC-DF set to 1, the receiving PE and by induction all the other
PEs in the ES will proceed to do DF Election as per the HRW PEs in the ES will proceed to do DF Election as per the HRW
Algorithm and following the AC-DF procedures. Algorithm and following the AC-DF procedures.
- Otherwise if even a single advertisement for the type-4 route is - Otherwise if even a single advertisement for the type-4 route is
not received with the locally configured DF Alg and capability, not received with the locally configured DF Alg and capability,
the default DF Election algorithm (modulus) algorithm MUST be the Default DF Election algorithm (modulus) algorithm MUST be
used as in [RFC7432]. used as in [RFC7432]. This procedure handles the case where
participating PEs in the ES disagree about the DF algorithm and
capability to apply.
- The absence of the DF Election Extended Community MUST be - The absence of the DF Election Extended Community MUST be
interpreted by a receiving PE as an indication of the default DF interpreted by a receiving PE as an indication of the Default DF
Election algorithm on the sending PE, that is, DF Alg 0 and no DF Election algorithm on the sending PE, that is, DF Alg 0 and no DF
Election capabilities. Election capabilities.
o When all the PEs in an ES advertise DF Type 31, they will rely on o When all the PEs in an ES advertise DF Type 31, they will rely on
the local policy to decide how to proceed with the DF Election. the local policy to decide how to proceed with the DF Election.
o For any new capability defined in the future, the o For any new capability defined in the future, the
applicability/compatibility of this new capability to the existing applicability/compatibility of this new capability to the existing
DF Algs must be assessed on a case by case basis. DF Algs must be assessed on a case by case basis.
o Likewise, for any new DF Alg defined in future, its o Likewise, for any new DF Alg defined in future, its
applicability/compatibility to the existing capabilities must be applicability/compatibility to the existing capabilities must be
assessed on a case by case basis. assessed on a case by case basis.
3.3 Auto-Derivation of ES-Import Route Target 3.2.1. Backward Compatibility
[RFC7432] implementations (i.e., those that predate this
specification) will not advertise the DF Election Extended Community.
That means that all other participating PEs in the ES will not
receive DF preferences and will revert to the Default DF Election
algorithm without AC-Influenced DF Election.
Similarly, a [RFC7432] implementation receiving a DF Election
Extended Community will ignore it and will continue to use the
Default DF Election algorithm.
3.3. Auto-Derivation of ES-Import Route Target
Section 7.6 of [RFC7432] describes how the value of the ES-Import Section 7.6 of [RFC7432] describes how the value of the ES-Import
Route Target for ESI types 1, 2, and 3 can be auto-derived by using Route Target for ESI types 1, 2, and 3 can be auto-derived by using
the high-order six bytes of the nine byte ESI value. The same auto- the high-order six bytes of the nine byte ESI value. The same auto-
derivation procedure can be extended to ESI types 0, 4, and 5 as long derivation procedure can be extended to ESI types 0, 4, and 5 as long
as it is ensured that the auto-derived values for ES-Import RT among as it is ensured that the auto-derived values for ES-Import RT among
different ES types don't overlap. different ES types don't overlap.
4. The Highest Random Weight DF Election Algorithm 4. The Highest Random Weight DF Election Algorithm
The procedure discussed in this section is applicable to the DF The procedure discussed in this section is applicable to the DF
Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire
Services [RFC8214]. Services [RFC8214].
Highest Random Weight (HRW) as defined in [HRW1999] is originally Highest Random Weight (HRW) as defined in [HRW1999] is originally
proposed in the context of Internet Caching and proxy Server load proposed in the context of Internet Caching and proxy Server load
balancing. Given an object name and a set of servers, HRW maps a balancing. Given an object name and a set of servers, HRW maps a
request to a server using the object-name (object-id) and server-name request to a server using the object-name (object-id) and server-name
(server-id) rather than the state of the server states. HRW forms a (server-id) rather than the server states. HRW forms a hash out of
hash out of the server-id and the object-id and forms an ordered list the server-id and the object-id and forms an ordered list of the
of the servers for the particular object-id. The server for which the servers for the particular object-id. The server for which the hash
hash value is highest, serves as the primary responsible for that value is highest, serves as the primary responsible for that
particular object, and the server with the next highest value in that particular object, and the server with the next highest value in that
hash serves as the backup server. HRW always maps a given object name hash serves as the backup server. HRW always maps a given object name
to the same server within a given cluster; consequently it can be to the same server within a given cluster; consequently it can be
used at client sites to achieve global consensus on object-server used at client sites to achieve global consensus on object-server
mappings. When that server goes down, the backup server becomes the mappings. When that server goes down, the backup server becomes the
responsible designate. responsible designate.
Choosing an appropriate hash function that is statistically oblivious Choosing an appropriate hash function that is statistically oblivious
to the key distribution and imparts a good uniform distribution of to the key distribution and imparts a good uniform distribution of
the hash output is an important aspect of the algorithm. Fortunately the hash output is an important aspect of the algorithm. Fortunately
many such hash functions exist. [HRW1999] provides pseudo-random many such hash functions exist. [HRW1999] provides pseudo-random
functions based on Unix utilities rand and srand and easily functions based on the Unix utilities rand and srand and easily
constructed XOR functions that perform considerably well. This constructed XOR functions that perform considerably well. This
imparts very good properties in the load balancing context. Also each imparts very good properties in the load balancing context. Also each
server independently and unambiguously arrives at the primary server server independently and unambiguously arrives at the primary server
selection. HRW already finds use in multicast and ECMP [RFC2991], selection. HRW already finds use in multicast and ECMP [RFC2991],
[RFC2992]. [RFC2992].
4.1. HRW and Consistent Hashing 4.1. HRW and Consistent Hashing
HRW is not the only algorithm that addresses the object to server HRW is not the only algorithm that addresses the object to server
mapping problem with goals of fair load distribution, redundancy and mapping problem with goals of fair load distribution, redundancy and
fast access. There is another family of algorithms that also fast access. There is another family of algorithms that also
addresses this problem; these fall under the umbrella of the addresses this problem; these fall under the umbrella of the
Consistent Hashing Algorithms [CHASH]. These will not be considered Consistent Hashing Algorithms [CHASH]. These will not be considered
here. here.
4.2. HRW Algorithm for EVPN DF Election 4.2. HRW Algorithm for EVPN DF Election
This section describes the application of HRW to DF election. Let This section describes the application of HRW to DF election. Let
DF(v) denote the Designated Forwarder and BDF(v) the Backup DF(v) denote the Designated Forwarder and BDF(v) the Backup
Designated forwarder for the Ethernet Tag v, where v is the VLAN, Si Designated forwarder for the Ethernet Tag v, where v is the VLAN, Si
is the IP address of server i, Es denotes the Ethernet Segment is the IP address of PE i, Es denotes the Ethernet Segment Identifier
Identifier and weight is a function of v, Si, and Es. and weight is a function of v, Si, and Es.
Note that while the DF election algorithm in [RFC7432] uses PE Note that while the DF election algorithm in [RFC7432] uses PE
address and vlan as inputs, this document uses Ethernet Tag, PE address and vlan as inputs, this document uses Ethernet Tag, PE
address and ESI as inputs. This is because if the same set of PEs are address and ESI as inputs. This is because if the same set of PEs are
multi-homed to the same set of ESes, then the DF election algorithm multi-homed to the same set of ESes, then the DF election algorithm
used in [RFC7432] would result in the same PE being elected DF for used in [RFC7432] would result in the same PE being elected DF for
the same set of broadcast domains on each ES, which can have adverse the same set of broadcast domains on each ES, which can have adverse
side-effects on both load balancing and redundancy. Including ESI in side-effects on both load balancing and redundancy. Including ESI in
the DF election algorithm introduces additional entropy which the DF election algorithm introduces additional entropy which
significantly reduces the probability of the same PE being elected DF significantly reduces the probability of the same PE being elected DF
for the same set of broadcast domains on each ES. Therefore, the ESI for the same set of broadcast domains on each ES. Therefore, the ESI
value in the Weight function below SHOULD be set to that of value in the Weight function below SHOULD be set to that of
corresponding ES. The ESI value MAY be set to all 0's in the Weight corresponding ES. The ESI value MAY be set to all 0's in the Weight
function below if the operator chooses so. function below if the operator so chooses.
In case of a VLAN-Bundle service, v denotes the lowest VLAN similar In case of a VLAN Bundle service, v denotes the lowest VLAN similar
to the 'lowest VLAN in bundle' logic of [RFC7432]. to the 'lowest VLAN in bundle' logic of [RFC7432].
1. DF(v) = Si: Weight(v, Es, Si) >= Weight(v, Es, Sj), for all j. In 1. DF(v) = Si: Weight(v, Es, Si) >= Weight(v, Es, Sj), for all j. In
case of a tie, choose the PE whose IP address is numerically the case of a tie, choose the PE whose IP address is numerically the
least. Note 0 <= i,j <= Number of PEs in the redundancy group. least. Note 0 <= i,j < Number of PEs in the redundancy group.
2. BDF(v) = Sk: Weight(v, Es, Si) >= Weight(V, Es, Sk) and Weight(v, 2. BDF(v) = Sk: Weight(v, Es, Si) >= Weight(v, Es, Sk) and Weight(v,
Es, Sk) >= Weight(v, Es, Sj). In case of tie choose the PE whose Es, Sk) >= Weight(v, Es, Sj). In case of tie choose the PE whose
IP address is numerically the least. IP address is numerically the least.
Since the Weight is a Pseudo-random function with domain as the Since the Weight is a pseudo-random function with domain as the
three-tuple (v, Es, S), it is an efficient deterministic algorithm three-tuple (v, Es, S), it is an efficient and deterministic
that is independent of the Ethernet Tag v sample space distribution. algorithm that is independent of the Ethernet Tag v sample space
Choosing a good hash function for the pseudo-random function is an distribution. Choosing a good hash function for the pseudo-random
important consideration for this algorithm to perform better than the function is an important consideration for this algorithm to perform
default algorithm. As mentioned previously, such functions are better than the Default algorithm. As mentioned previously, such
described in the HRW paper. We take as candidate hash functions two functions are described in the HRW paper. We take as candidate hash
of the ones that are preferred in [HRW1999]. function the first one out of the two that are preferred in
[HRW1999]:
1. Wrand(v, Es, Si) = (1103515245((1103515245.Si+12345)XOR
D(v,Es))+12345)(mod 2^31) and
2. Wrand2(v, Es, Si) = (1103515245((1103515245.D(v,Es)+12345)XOR Wrand(v, Es, Si) = (1103515245((1103515245.Si+12345) XOR
Si)+12345)(mod 2^31) D(v,Es))+12345)(mod 2^31)
Here D(v,Es) is the 31-bit digest (CRC-32 and discarding the MSB as Here D(v,Es) is the 31-bit digest (CRC-32 and discarding the MSB as
in [HRW1999]) of the 14-byte stream, the Ethernet Tag v (4 bytes) in [HRW1999]) of the 14-byte stream, the Ethernet Tag v (4 bytes)
followed by the Ethernet Segment Identifier (10 bytes). It is followed by the Ethernet Segment Identifier (10 bytes). It is
mandated that the 14-byte stream is formed by concatenation of the mandated that the 14-byte stream is formed by concatenation of the
Ethernet tag and the Ethernet Segment identifier in network byte Ethernet tag and the Ethernet Segment identifier in network byte
order. The CRC should proceed as if the stream is in network byte order. The CRC should proceed as if the stream is in network byte
order (big-endian). Si is address of the ith server. The server's IP order (big-endian). Si is address of the ith server. The server's IP
address length does not matter as only the low-order 31 bits are address length does not matter as only the low-order 31 bits are
modulo significant. Although both the above hash functions perform modulo significant.
similarly, we select the first hash function (1) of choice, as the
hash function has to be the same in all the PEs participating in the
DF election.
A point to note is that the Weight function takes into consideration A point to note is that the Weight function takes into consideration
the combination of the Ethernet Tag, Ethernet Segment and the PE IP- the combination of the Ethernet Tag, Ethernet Segment and the PE IP-
address, and the actual length of the server IP address (whether V4 address, and the actual length of the server IP address (whether IPv4
or V6) is not really relevant. The default algorithm in [RFC7432] or IPv6) is not really relevant. The Default algorithm in [RFC7432]
cannot employ both V4 and V6 PE addresses, since [RFC7432] does not cannot employ both IPv4 and IPv6 PE addresses, since [RFC7432] does
specify how to decide on the ordering (the ordinal list) when both V4 not specify how to decide on the ordering (the ordinal list) when
and V6 PEs are present. both IPv4 and IPv6 PEs are present.
HRW solves the disadvantage pointed out in Section 2.2.1 and ensures: HRW solves the disadvantages pointed out in Section 2.2.1 and
ensures:
o with very high probability that the task of DF election for the o with very high probability that the task of DF election for the
VLANs configured on an ES is more or less equally distributed among VLANs configured on an ES is more or less equally distributed among
the PEs even for the 2 PE case. the PEs even for the 2 PE case.
o If a PE that is not the DF or the BDF for that VLAN, goes down or o If a PE that is not the DF or the BDF for that VLAN, goes down or
its connection to the ES goes down, it does not result in a DF or its connection to the ES goes down, it does not result in a DF or
BDF reassignment. This saves computation, especially in the case BDF reassignment. This saves computation, especially in the case
when the connection flaps. when the connection flaps.
o More importantly it avoids the needless disruption case of Section o More importantly it avoids the needless disruption case of Section
2.2.1 (3), that is inherent in the existing default DF Election. 2.2.1 (3), that is inherent in the existing Default DF Election.
o In addition to the DF, the algorithm also furnishes the BDF, which o In addition to the DF, the algorithm also furnishes the BDF, which
would be the DF if the current DF fails. would be the DF if the current DF fails.
5. The Attachment Circuit Influenced DF Election Capability 5. The Attachment Circuit Influenced DF Election Capability
The procedure discussed in this section is applicable to the DF The procedure discussed in this section is applicable to the DF
Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire
Services [RFC8214]. Services [RFC8214].
The AC-DF capability MAY be used with any "DF Alg" algorithm. It MUST The AC-DF capability MAY be used with any "DF Alg" algorithm. It MUST
modify the DF Election procedures by removing from consideration any modify the DF Election procedures by removing from consideration any
candidate PE in the ES that cannot forward traffic on the AC that candidate PE in the ES that cannot forward traffic on the AC that
belongs to the BD. This section is applicable to VLAN-Based and VLAN- belongs to the BD. This section is applicable to VLAN-Based and VLAN
Bundle service interfaces. Section 5.1 describes the procedures for Bundle service interfaces. Section 5.1 describes the procedures for
VLAN-Aware Bundle interfaces. VLAN-Aware Bundle interfaces.
In particular, when used with the default DF Alg, the AC-DF In particular, when used with the Default DF Alg, the AC-DF
capability modifies the Step 3 in the DF Election procedure described capability modifies the Step 3 in the DF Election procedure described
in [RFC7432] Section 8.5, as follows: in [RFC7432] Section 8.5, as follows:
3. When the timer expires, each PE builds an ordered "candidate" list 3. When the timer expires, each PE builds an ordered "candidate" list
of the IP addresses of all the PE nodes attached to the Ethernet of the IP addresses of all the PE nodes attached to the Ethernet
Segment (including itself), in increasing numeric value. The Segment (including itself), in increasing numeric value. The
candidate list is based on the Originator Router's IP addresses of candidate list is based on the Originator Router's IP addresses of
the ES routes, but excludes any PE from whom no Ethernet A-D per the ES routes, but excludes any PE from whom no Ethernet A-D per
ES route has been received, or from whom the route has been ES route has been received, or from whom the route has been
withdrawn. Afterwards, the DF Election algorithm is applied on a withdrawn. Afterwards, the DF Election algorithm is applied on a
per <ES,VLAN> or <ES,VLAN-bundle>, however, the IP address for a per <ES,VLAN> or <ES,VLAN Bundle>, however, the IP address for a
PE will not be considered candidate for a given <ES,VLAN> or PE will not be considered candidate for a given <ES,VLAN> or
<ES,VLAN-bundle> until the corresponding Ethernet A-D per EVI <ES,VLAN Bundle> until the corresponding Ethernet A-D per EVI
route has been received from that PE. In other words, the ACS on route has been received from that PE. In other words, the ACS on
the ES for a given PE must be UP so that the PE is considered as the ES for a given PE must be UP so that the PE is considered as
candidate for a given BD. candidate for a given BD.
The above paragraph differs from [RFC7432] Section 8.5, Step 3, in The above paragraph differs from [RFC7432] Section 8.5, Step 3, in
two aspects: two aspects:
o Any DF Alg algorithm can be used, and not only the modulus-based o Any DF Alg algorithm can be used, and not only the modulus-based
one (which is the default DF Election, or DF Alg 0 in this one (which is the Default DF Election, or DF Alg 0 in this
document). document).
o The candidate list is pruned based upon non-receipt of Ethernet A-D o The candidate list is pruned based upon non-receipt of Ethernet A-D
routes: a PE's IP address MUST be removed from the ES candidate routes: a PE's IP address MUST be removed from the ES candidate
list if its Ethernet A-D per ES route is withdrawn. A PE's IP list if its Ethernet A-D per ES route is withdrawn. A PE's IP
address MUST NOT be considered as candidate DF for a <ES,VLAN> or address MUST NOT be considered as candidate DF for a <ES,VLAN> or
<ES,VLAN-bundle>, if its Ethernet A-D per EVI route for the <ES,VLAN Bundle>, if its Ethernet A-D per EVI route for the
<ES,VLAN> or <ES,VLAN-bundle> respectively, is withdrawn. <ES,VLAN> or <ES,VLAN Bundle> respectively, is withdrawn.
The following example illustrates the AC-DF behavior applied to the The following example illustrates the AC-DF behavior applied to the
Default DF election algorithm, assuming the network in Figure 2: Default DF election algorithm, assuming the network in Figure 2:
a) When PE1 and PE2 discover ES12, they advertise an ES route for a) When PE1 and PE2 discover ES12, they advertise an ES route for
ES12 with the associated ES-import extended community and the DF ES12 with the associated ES-import extended community and the DF
Election Extended Community indicating AC-DF=1; they start a timer Election Extended Community indicating AC-DF=1; they start a timer
at the same time. Likewise, PE2 and PE3 advertise an ES route for at the same time. Likewise, PE2 and PE3 advertise an ES route for
ES23 with AC-DF=1 and start a timer. ES23 with AC-DF=1 and start a timer.
b) PE1/PE2 advertise an Ethernet A-D per ES route for ES12, and b) PE1/PE2 advertise an Ethernet A-D per ES route for ES12, and
PE2/PE3 advertise an Ethernet A-D per ES route for ES23. PE2/PE3 advertise an Ethernet A-D per ES route for ES23.
c) In addition, PE1/PE2/PE3 advertise an Ethernet A-D per EVI route c) In addition, PE1/PE2/PE3 advertise an Ethernet A-D per EVI route
for AC1, AC2, AC3 and AC4 as soon as the ACs are enabled. Note for AC1, AC2, AC3 and AC4 as soon as the ACs are enabled. Note
that the AC can be associated to a single customer VID (e.g. VLAN- that the AC can be associated to a single customer VID (e.g. VLAN-
based service interfaces) or a bundle of customer VIDs (e.g. VLAN- based service interfaces) or a bundle of customer VIDs (e.g. VLAN
Bundle service interfaces). Bundle service interfaces).
d) When the timer expires, each PE builds an ordered "candidate" list d) When the timer expires, each PE builds an ordered "candidate" list
of the IP addresses of all the PE nodes connected to the Ethernet of the IP addresses of all the PE nodes connected to the Ethernet
Segment (including itself) as explained above in [RFC7432] Step 3. Segment (including itself) as explained above in [RFC7432] Step 3.
Any PE from which an Ethernet A-D per ES route has not been Any PE from which an Ethernet A-D per ES route has not been
received is pruned from the list. received is pruned from the list.
e) When electing the DF for a given BD, a PE will not be considered e) When electing the DF for a given BD, a PE will not be considered
candidate until an Ethernet A-D per EVI route has been received candidate until an Ethernet A-D per EVI route has been received
from that PE. In other words, the ACS on the ES for a given PE from that PE. In other words, the ACS on the ES for a given PE
must be UP so that the PE is considered as candidate for a given must be UP so that the PE is considered as candidate for a given
BD. For example, PE1 will not consider PE2 as candidate for DF BD. For example, PE1 will not consider PE2 as candidate for DF
election for <ES12,VLAN-1> until an Ethernet A-D per EVI route is election for <ES12,VLAN-1> until an Ethernet A-D per EVI route is
received from PE2 for <ES12,VLAN-1>. received from PE2 for <ES12,VLAN-1>.
skipping to change at page 21, line 27 skipping to change at page 22, line 8
the candidate list, the DF Election can be applied for the the candidate list, the DF Election can be applied for the
remaining N candidates. remaining N candidates.
Note that this procedure only modifies the existing EVPN control Note that this procedure only modifies the existing EVPN control
plane by adding and processing the DF Election Extended Community, plane by adding and processing the DF Election Extended Community,
and by pruning the candidate list of PEs that take part in the DF and by pruning the candidate list of PEs that take part in the DF
election. election.
In addition to the events defined in the FSM in Section 3.1, the In addition to the events defined in the FSM in Section 3.1, the
following events SHALL modify the candidate PE list and trigger the following events SHALL modify the candidate PE list and trigger the
DF re-election in a PE for a given <ES,VLAN> or <ES,VLAN-Bundle>. In DF re-election in a PE for a given <ES,VLAN> or <ES,VLAN Bundle>. In
the FSM of Figure 3, the events below MUST trigger a transition from the FSM of Figure 3, the events below MUST trigger a transition from
DF_DONE to DF_CALC: DF_DONE to DF_CALC:
i. Local AC going DOWN/UP. i. Local AC going DOWN/UP.
ii. Reception of a new Ethernet A-D per EVI update/withdraw for the ii. Reception of a new Ethernet A-D per EVI update/withdraw for the
<ES,VLAN> or <ES,VLAN-Bundle>. <ES,VLAN> or <ES,VLAN Bundle>.
iii. Reception of a new Ethernet A-D per ES update/withdraw for the iii. Reception of a new Ethernet A-D per ES update/withdraw for the
ES. ES.
5.1. AC-Influenced DF Election Capability For VLAN-Aware Bundle Services 5.1. AC-Influenced DF Election Capability For VLAN-Aware Bundle Services
The procedure described section 5 works for VLAN-based and The procedure described in section 5 works for VLAN-based and VLAN
VLAN-Bundle service interfaces since, for those service types, a PE Bundle service interfaces since, for those service types, a PE
advertises only one Ethernet A-D per EVI route per <ES,VLAN> or advertises only one Ethernet A-D per EVI route per <ES,VLAN> or
<ES,VLAN-Bundle>. The withdrawal of such route means that the PE <ES,VLAN Bundle>. The withdrawal of such route means that the PE
cannot forward traffic on that particular <ES,VLAN> or cannot forward traffic on that particular <ES,VLAN> or <ES,VLAN
<ES,VLAN-Bundle>, therefore the PE can be removed from consideration Bundle>, therefore the PE can be removed from consideration for DF.
for DF.
According to [RFC7432], in VLAN-aware bundle services, the PE According to [RFC7432], in VLAN-aware Bundle services, the PE
advertises multiple Ethernet A-D per EVI routes per <ES,VLAN-Bundle> advertises multiple Ethernet A-D per EVI routes per <ES,VLAN Bundle>
(one route per Ethernet Tag), while the DF Election is still (one route per Ethernet Tag), while the DF Election is still
performed per <ES,VLAN-Bundle>. The withdrawal of an individual route performed per <ES,VLAN Bundle>. The withdrawal of an individual route
only indicates the unavailability of a specific AC but not only indicates the unavailability of a specific AC but not
necessarily all the ACs in the <ES,VLAN-Bundle>. necessarily all the ACs in the <ES,VLAN Bundle>.
This document modifies the DF Election for VLAN-Aware Bundle services This document modifies the DF Election for VLAN-Aware Bundle services
in the following way: in the following way:
o After confirming that all the PEs in the ES advertise the AC-DF o After confirming that all the PEs in the ES advertise the AC-DF
capability, a PE will perform a DF Election per <ES,VLAN>, as capability, a PE will perform a DF Election per <ES,VLAN>, as
opposed to per <ES,VLAN-Bundle> in [RFC7432]. Now, the withdrawal opposed to per <ES,VLAN Bundle> in [RFC7432]. Now, the withdrawal
of an Ethernet A-D per EVI route for a VLAN will indicate that the of an Ethernet A-D per EVI route for a VLAN will indicate that the
advertising PE's ACS is DOWN and the rest of the PEs in the ES can advertising PE's ACS is DOWN and the rest of the PEs in the ES can
remove the PE from consideration for DF in the <ES,VLAN>. remove the PE from consideration for DF in the <ES,VLAN>.
o The PEs will now follow the procedures in section 5. o The PEs will now follow the procedures in section 5.
For example, assuming three bridge tables in PE1 for the same MAC-VRF For example, assuming three Bridge Tables in PE1 for the same MAC-VRF
(each one associated to a different Ethernet Tag, e.g. VLAN-1, VLAN-2 (each one associated to a different Ethernet Tag, e.g. VLAN-1, VLAN-2
and VLAN-3), PE1 will advertise three Ethernet A-D per EVI routes for and VLAN-3), PE1 will advertise three Ethernet A-D per EVI routes for
ES12. Each of the three routes will indicate the status of each of ES12. Each of the three routes will indicate the status of each of
the three ACs in ES12. PE1 will be considered as a valid candidate PE the three ACs in ES12. PE1 will be considered as a valid candidate PE
for DF election in <ES12,VLAN-1>, <ES12,VLAN-2>, <ES12,VLAN-3> as for DF Election in <ES12,VLAN-1>, <ES12,VLAN-2>, <ES12,VLAN-3> as
long as its three routes are active. For instance, if PE1 withdraws long as its three routes are active. For instance, if PE1 withdraws
the Ethernet A-D per EVI routes for <ES12,VLAN-1>, the PEs in ES12 the Ethernet A-D per EVI routes for <ES12,VLAN-1>, the PEs in ES12
will not consider PE1 as a suitable DF candidate for <ES12,VLAN-1>. will not consider PE1 as a suitable DF candidate for <ES12,VLAN-1>.
PE1 will still be considered for <ES12,VLAN-2> and <ES12,VLAN-3> PE1 will still be considered for <ES12,VLAN-2> and <ES12,VLAN-3>
since its routes are active. since its routes are active.
6. Solution Benefits 6. Solution Benefits
The solution described in this document provides the following The solution described in this document provides the following
benefits: benefits:
a) Extends the DF Election in [RFC7432] to address the unfair load- a) Extends the DF Election in [RFC7432] to address the unfair load-
balancing and potential black-holing issues of the default DF balancing and potential black-holing issues of the Default DF
Election algorithm. The solution is applicable to the DF Election Election algorithm. The solution is applicable to the DF Election
in EVPN Services [RFC7432] and EVPN Virtual Private Wire Services in EVPN Services [RFC7432] and EVPN Virtual Private Wire Services
[RFC8214]. [RFC8214].
b) It defines a way to signal the DF Election algorithm and b) It defines a way to signal the DF Election algorithm and
capabilities intended by the advertising PE. This is done by capabilities intended by the advertising PE. This is done by
defining the DF Election Extended Community, which allow signaling defining the DF Election Extended Community, which allow signaling
of the capabilities supported by this document as well as any of the capabilities supported by this document as well as any
other future DF Election algorithms and capabilities. other future DF Election algorithms and capabilities.
skipping to change at page 23, line 19 skipping to change at page 23, line 47
procedures described in [RFC7432] by defining a new DF Election procedures described in [RFC7432] by defining a new DF Election
framework. In general, this framework allows the PEs that are part of framework. In general, this framework allows the PEs that are part of
the same Ethernet Segment to exchange additional information and the same Ethernet Segment to exchange additional information and
agree on the DF Election Type and Capabilities to be used. agree on the DF Election Type and Capabilities to be used.
Following the procedures in this document, the operator will minimize Following the procedures in this document, the operator will minimize
undesired situations such as unfair load-balancing, service undesired situations such as unfair load-balancing, service
disruption and traffic black-holing. Since those situations may have disruption and traffic black-holing. Since those situations may have
been purposely created by a malicious user with access to the been purposely created by a malicious user with access to the
configuration of one PE, this document enhances also the security of configuration of one PE, this document enhances also the security of
the network. In addition, the new framework is extensible and allows the network. Note that the network will not benefit of the new
for future new security enhancements that are out of the scope of procedures if the configuration of one of the PEs in the ES is
this document. Finally, since this document extends the procedures in changed to the Default [RFC7432] DF Election.
[RFC7432], the same Security Considerations described in [RFC7432]
are valid for this document. In addition, the new framework is extensible and allows for future
new security enhancements that are out of the scope of this document.
Finally, since this document extends the procedures in [RFC7432], the
same Security Considerations described in [RFC7432] are valid for
this document.
8. IANA Considerations 8. IANA Considerations
IANA is requested to: IANA is requested to:
o Allocate Sub-Type value 0x06 in the "EVPN Extended Community Sub- o Allocate Sub-Type value 0x06 in the "EVPN Extended Community Sub-
Types" registry defined in [RFC7153] as follows: Types" registry defined in [RFC7153] as follows:
SUB-TYPE VALUE NAME Reference SUB-TYPE VALUE NAME Reference
-------------- ------------------------- ------------- -------------- ------------------------- -------------
0x06 DF Election Extended Community This document 0x06 DF Election Extended Community This document
o Set up a registry called "DF Alg" for the DF Alg octet in the o Set up a registry called "DF Alg" for the DF Alg field in the
Extended Community. New registrations will be made through the "RFC Extended Community. New registrations will be made through the "RFC
Required" procedure defined in [RFC8126]. The following initial Required" procedure defined in [RFC8126]. Value 31 is for
values in that registry are requested: Experimental use and does not require any other RFC than this
document. The following initial values in that registry are
requested:
Alg Name Reference Alg Name Reference
---- -------------- ------------- ---- -------------- -------------
0 Default DF Election This document 0 Default DF Election This document
1 HRW algorithm This document 1 HRW algorithm This document
2-30 Unassigned 2-30 Unassigned
31 Reserved for Experimental use This document 31 Reserved for Experimental use This document
o Set up a registry called "DF Election Capabilities" for the two- o Set up a registry called "DF Election Capabilities" for the two-
octet Bitmap field in the Extended Community. New registrations octet Bitmap field in the Extended Community. New registrations
skipping to change at page 24, line 28 skipping to change at page 25, line 16
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet
VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015, VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015,
<https://www.rfc-editor.org/info/rfc7432>. <https://www.rfc-editor.org/info/rfc7432>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J. [RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet VPN", RFC Rabadan, "Virtual Private Wire Service Support in Ethernet VPN", RFC
8214, DOI 10.17487/RFC8214, August 2017, <https://www.rfc- 8214, DOI 10.17487/RFC8214, August 2017, <https://www.rfc-
editor.org/info/rfc8214>. editor.org/info/rfc8214>.
[HRW1999] Thaler, D. and C. Ravishankar, "Using Name-Based Mappings
to Increase Hit Rates", IEEE/ACM Transactions in networking Volume 6
Issue 1, February 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
1997, <https://www.rfc-editor.org/info/rfc2119>. 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>. <https://www.rfc-editor.org/info/rfc8174>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February
skipping to change at page 25, line 29 skipping to change at page 26, line 13
ISBN 0-262-03384-4., February 2009. ISBN 0-262-03384-4., February 2009.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and [RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, DOI 10.17487/RFC2991, Multicast Next-Hop Selection", RFC 2991, DOI 10.17487/RFC2991,
November 2000, <http://www.rfc-editor.org/info/rfc2991>. November 2000, <http://www.rfc-editor.org/info/rfc2991>.
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path [RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path
Algorithm", RFC 2992, DOI 10.17487/RFC2992, November 2000, Algorithm", RFC 2992, DOI 10.17487/RFC2992, November 2000,
<http://www.rfc-editor.org/info/rfc2992>. <http://www.rfc-editor.org/info/rfc2992>.
[HRW1999] Thaler, D. and C. Ravishankar, "Using Name-Based Mappings
to Increase Hit Rates", IEEE/ACM Transactions in networking Volume 6
Issue 1, February 1998, <https://www.microsoft.com/en-us/research/wp-
content/uploads/2017/02/HRW98.pdf>.
10. Acknowledgments 10. Acknowledgments
The authors want to thank Sriram Venkateswaran, Laxmi Padakanti, The authors want to thank Sriram Venkateswaran, Laxmi Padakanti,
Ranganathan Boovaraghavan, Tamas Mondal, Sami Boutros, Jakob Heitz, Ranganathan Boovaraghavan, Tamas Mondal, Sami Boutros, Jakob Heitz,
Mrinmoy Ghosh, Leo Mermelstein, Mankamana Mishra and Samir Thoria for Mrinmoy Ghosh, Leo Mermelstein, Mankamana Mishra, Anoop Ghanwani and
their review and contributions. Special thanks to Stephane Litkowski Samir Thoria for their review and contributions. Special thanks to
for his thorough review and detailed contributions. Stephane Litkowski for his thorough review and detailed
contributions.
11. Contributors 11. Contributors
In addition to the authors listed on the front page, the following In addition to the authors listed on the front page, the following
coauthors have also contributed to this document: coauthors have also contributed to this document:
Antoni Przygienda Antoni Przygienda
Juniper Networks, Inc. Juniper Networks, Inc.
1194 N. Mathilda Drive 1194 N. Mathilda Drive
Sunnyvale, CA 95134 Sunnyvale, CA 95134
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