draft-ietf-pim-drlb-08.txt   draft-ietf-pim-drlb-09.txt 
Network Working Group Yiqun. Cai Network Working Group Y. Cai
Internet-Draft Heidi. Ou Internet-Draft H. Ou
Intended status: Standards Track Alibaba Group Intended status: Standards Track Alibaba Group
Expires: December 21, 2018 Sri. Vallepalli Expires: April 25, 2019 S. Vallepalli
Mankamana. Mishra M. Mishra
Stig. Venaas S. Venaas
Cisco Systems Cisco Systems, Inc.
Andy. Green A. Green
British Telecom British Telecom
June 19, 2018 October 22, 2018
PIM Designated Router Load Balancing PIM Designated Router Load Balancing
draft-ietf-pim-drlb-08 draft-ietf-pim-drlb-09
Abstract Abstract
On a multi-access network, one of the PIM routers is elected as a On a multi-access network, one of the PIM routers is elected as a
Designated Router (DR). On the last hop LAN, the PIM DR is Designated Router (DR). On the last hop LAN, the PIM DR is
responsible for tracking local multicast listeners and forwarding responsible for tracking local multicast listeners and forwarding
traffic to these listeners if the group is operating in PIM-SM. In traffic to these listeners if the group is operating in PIM-SM. This
this document, we propose a modification to the PIM-SM protocol that document specifies a modification to the PIM-SM protocol that allows
allows more than one of these last hop routers to be selected so that more than one of these last hop routers to be selected, so that the
the forwarding load can be distributed among these routers. forwarding load can be distributed among these routers.
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 21, 2018. This Internet-Draft will expire on April 25, 2019.
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
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 24 skipping to change at page 2, line 24
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 6 4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 6
4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . 6 4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . 6
4.2. Hash Mask and Hash Algorithm . . . . . . . . . . . . . . 7 4.2. Hash Mask and Hash Algorithm . . . . . . . . . . . . . . 7
4.3. Modulo Hash Algorithm . . . . . . . . . . . . . . . . . . 8 4.3. Modulo Hash Algorithm . . . . . . . . . . . . . . . . . . 8
4.3.1. Limitations . . . . . . . . . . . . . . . . . . . . . 9
4.4. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 9 4.4. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 9
5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . 9 5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . 10
5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 9 5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 10
5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option . . . . 10 5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option . . . . 10
6. Protocol Specification . . . . . . . . . . . . . . . . . . . 11 6. Protocol Specification . . . . . . . . . . . . . . . . . . . 11
6.1. PIM DR Operation . . . . . . . . . . . . . . . . . . . . 11 6.1. PIM DR Operation . . . . . . . . . . . . . . . . . . . . 11
6.2. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 12 6.2. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 12
6.2.1. Router Receives New DRLBGDR . . . . . . . . . . . . . 13 6.2.1. Router Receives New DRLBGDR . . . . . . . . . . . . . 13
6.2.2. Router Receives Updated DRLBGDR . . . . . . . . . . . 13 6.2.2. Router Receives Updated DRLBGDR . . . . . . . . . . . 13
6.3. PIM Assert Modification . . . . . . . . . . . . . . . . . 14 6.3. PIM Assert Modification . . . . . . . . . . . . . . . . . 14
7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Manageability Considerations . . . . . . . . . . . . . . . . 15 8. Manageability Considerations . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9.1. Initial registry . . . . . . . . . . . . . . . . . . . . 16
9.2. Assignment of new message types . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . 17 12.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
On a multi-access LAN such as an Ethernet, one of the PIM routers is On a multi-access LAN such as an Ethernet, one of the PIM routers is
elected as a DR. The PIM DR has two roles in the PIM-SM protocol. elected as a DR. The PIM DR has two roles in the PIM-SM protocol.
On the first hop network, the PIM DR is responsible for registering On the first hop LAN, the PIM DR is responsible for registering an
an active source with the Rendezvous Point (RP) if the group is active source with the Rendezvous Point (RP) if the group is
operating in PIM-SM. On the last hop LAN, the PIM DR is responsible operating in PIM-SM. On the last hop LAN, the PIM DR is responsible
for tracking local multicast listeners and forwarding to these for tracking local multicast listeners and forwarding to these
listeners if the group is operating in PIM-SM. listeners if the group is operating in PIM-SM.
Consider the following last hop LAN in Figure 1: Consider the following last hop LAN in Figure 1:
( core networks ) (core networks)
| | | | | |
| | | | | |
R1 R2 R3 R1 R2 R3
| | | | | |
--(last hop LAN)-- --(last hop LAN)--
| |
| |
(many receivers) (many receivers)
Figure 1: Last Hop LAN Figure 1: Last Hop LAN
Assume R1 is elected as the Designated Router. According to Assume R1 is elected as the Designated Router. According to
[RFC4601], R1 will be responsible for forwarding traffic to that LAN [RFC7761], R1 will be responsible for forwarding traffic to that LAN
on behalf of any local members. In addition to keeping track of IGMP on behalf of any local members. In addition to keeping track of IGMP
and MLD membership reports, R1 is also responsible for initiating the and MLD membership reports, R1 is also responsible for initiating the
creation of source and/or shared trees towards the senders or the creation of source and/or shared trees towards the senders or the
RPs. RPs.
Forcing sole data plane forwarding responsibility on the PIM DR Forcing sole data plane forwarding responsibility on the PIM DR
uncovers a limitation in the protocol. In comparison, even though an uncovers a limitation in the protocol. In comparison, even though an
OSPF DR or an IS-IS DIS handles additional duties while running the OSPF DR or an IS-IS DIS handles additional duties while running the
OSPF or IS-IS protocols, they are not required to be solely OSPF or IS-IS protocols, they are not required to be solely
responsible for forwarding packets for the network. On the other responsible for forwarding packets for the network. On the other
hand, on a last hop LAN, only the PIM DR is asked to forward packets hand, on a last hop LAN, only the PIM DR is asked to forward packets
while the other routers handle only control traffic (and perhaps drop while the other routers handle only control traffic (and perhaps drop
packets due to RPF failures). Hence the forwarding load of a last packets due to RPF failures). Hence the forwarding load of a last
hop LAN is concentrated on a single router. hop LAN is concentrated on a single router.
This leads to several issues. One of the issues is that the This leads to several issues. One of the issues is that the
aggregated bandwidth will be limited to what R1 can handle towards aggregated bandwidth will be limited to what R1 can handle towards
this particular interface. It is very common that the last hop LAN this particular interface. It is very common that the last hop LAN
usually consists of switches that run IGMP/MLD or PIM snooping. This consists of switches that run IGMP/MLD or PIM snooping. This allows
allows the forwarding of multicast packets to be restricted only to the forwarding of multicast packets to be restricted only to segments
segments leading to receivers who have indicated their interest in leading to receivers who have indicated their interest in multicast
multicast groups using either IGMP or MLD. The emergence of the groups using either IGMP or MLD. The emergence of the switched
switched Ethernet allows the aggregated bandwidth to exceed, Ethernet allows the aggregated bandwidth to exceed, sometimes by a
sometimes by a large number, that of a single link. For example, let large number, that of a single link. For example, let us modify
us modify Figure 1 and introduce an Ethernet switch in Figure 2. Figure 1 and introduce an Ethernet switch in Figure 2.
( core networks ) (core networks)
| | | | | |
| | | | | |
R1 R2 R3 R1 R2 R3
| | | | | |
+=gi0===gi1===gi2=+ +=gi0===gi1===gi2=+
+ + + +
+ switch + + switch +
+ + + +
+=gi4===gi5===gi6=+ +=gi4===gi5===gi6=+
| | | | | |
skipping to change at page 4, line 31 skipping to change at page 4, line 31
router, R1, R2 and R3, and the switch have enough forwarding capacity router, R1, R2 and R3, and the switch have enough forwarding capacity
to handle hundreds of Gigabits of data. to handle hundreds of Gigabits of data.
Let us further assume that each of the hosts requests 500 Mbps of Let us further assume that each of the hosts requests 500 Mbps of
unique multicast data. This totals to 1.5 Gbps of data, which is unique multicast data. This totals to 1.5 Gbps of data, which is
less than what each switch or the combined uplink bandwidth across less than what each switch or the combined uplink bandwidth across
the routers can handle, even under failure of a single router. the routers can handle, even under failure of a single router.
On the other hand, the link between R1 and switch, via port gi0, can On the other hand, the link between R1 and switch, via port gi0, can
only handle a throughput of 1Gbps. And if R1 is the only DR (the PIM only handle a throughput of 1Gbps. And if R1 is the only DR (the PIM
DR elected using the procedure defined by [RFC4601]) at least 500 DR elected using the procedure defined by [RFC7761]) at least 500
Mbps worth of data will be lost because the only link that can be Mbps worth of data will be lost because the only link that can be
used to draw the traffic from the routers to the switch is via gi0. used to draw the traffic from the routers to the switch is via gi0.
In other words, the entire network's throughput is limited by the In other words, the entire network's throughput is limited by the
single connection between the PIM DR and the switch (or the last hop single connection between the PIM DR and the switch (or the last hop
LAN as in Figure 1). LAN as in Figure 1).
The problem may also manifest itself in a different way. For
example, R1 happens to forward 500 Mbps worth of unicast data to H1,
and at the same time, H2 and H3 each request 300 Mbps of different
multicast data. R1 experiences packet drop once again. while, in the
meantime, there is sufficient forwarding capacity left on R2 and R3
and unused link capacity between the switch and R2/R3.
Another important issue is related to failover. If R1 is the only Another important issue is related to failover. If R1 is the only
forwarder on the last hop router for shared LAN, when R1 goes out of forwarder on the last hop router for a shared LAN, when R1 goes out
service, multicast forwarding for the entire LAN has to be rebuilt by of service, multicast forwarding for the entire LAN has to be rebuilt
the newly elected PIM DR. However, if there was a way that allowed by the newly elected PIM DR. However, if there was a way that
multiple routers to forward to the LAN for different groups, failure allowed multiple routers to forward to the LAN for different groups,
of one of the routers would only lead to disruption to a subset of failure of one of the routers would only lead to disruption to a
the flows, therefore improving the overall resilience of the network. subset of the flows, therefore improving the overall resilience of
the network.
There is limitation in the hash algorithm used in this document, but There is a limitation in the hash algorithm used in this document,
this draft provides the option to have different and more consistent but this document provides the option to have different and more
hash algorithms in the future. consistent hash algorithms in the future.
In this document, we propose a modification to the PIM-SM protocol This document specifies a modification to the PIM-SM protocol that
that allows more than one of these routers, called Group Designated allows more than one of these routers, called Group Designated
Routers (GDR) to be selected so that the forwarding load can be Routers (GDR) to be selected so that the forwarding load can be
distributed among a number of routers. distributed among a number of routers.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
With respect to PIM, this document follows the terminology that has With respect to PIM, this document follows the terminology that has
been defined in [RFC4601]. been defined in [RFC7761].
This document also introduces the following new acronyms: This document also introduces the following new acronyms:
o GDR: GDR stands for "Group Designated Router". For each multicast o GDR: GDR stands for "Group Designated Router". For each multicast
flow, either a (*,G) for ASM, or an (S,G) for SSM, a hash flow, either a (*,G) for ASM, or an (S,G) for SSM, a hash
algorithm (described below) is used to select one of the routers algorithm (described below) is used to select one of the routers
as a GDR. The GDR is responsible for initiating the forwarding as a GDR. The GDR is responsible for initiating the forwarding
tree building process for the corresponding multicast flow. tree building process for the corresponding multicast flow.
o GDR Candidate: a last hop router that has the potential to become o GDR Candidate: a last hop router that has the potential to become
a GDR. A GDR Candidate must have the same DR priority and must a GDR. A GDR Candidate must have the same DR priority and must
run the same GDR election hash algorithm as the DR router. It run the same GDR election hash algorithm as the DR router. It
must send and process new PIM Hello Options as defined in this must send and process new PIM Hello Options as defined in this
document. There might be more than one GDR Candidate on a LAN, document. There might be more than one GDR Candidate on a LAN,
but only one can become GDR for a specific multicast flow. but only one can become GDR for a specific multicast flow.
3. Applicability 3. Applicability
The proposed change described in this specification applies to PIM-SM The extension specified in this document applies to PIM-SM last hop
last hop routers only. routers only. It does not alter the behavior of a PIM DR on the
first hop network. This is because the source tree is built using
It does not alter the behavior of a PIM DR on the first hop network. the IP address of the sender, not the IP address of the PIM DR that
This is because the source tree is built using the IP address of the sends the registers towards the RP. The load balancing between first
sender, not the IP address of the PIM DR that sends the registers hop routers can be achieved naturally if an IGP provides equal cost
towards the RP. The load balancing between first hop routers can be multiple paths (which it usually does in practice). Also
achieved naturally if an IGP provides equal cost multiple paths distributing the load to do registering does not justify the
(which it usually does in practice). Also distributing the load to additional complexity required to support it.
do registering does not justify the additional complexity required to
support it.
4. Functional Overview 4. Functional Overview
In the existing PIM DR election, when multiple last hop routers are In the PIM DR election as defined in [RFC7761], when multiple last
connected to a multi-access LAN (for example, an Ethernet), one of hop routers are connected to a multi-access LAN (for example, an
them is selected to act as PIM DR. The PIM DR is responsible for Ethernet), one of them is elected to act as PIM DR. The PIM DR is
sending local Join/Prune messages towards the RP or source. In order responsible for sending local Join/Prune messages towards the RP or
to elect the PIM DR, each PIM router on the LAN examines the received source. In order to elect the PIM DR, each PIM router on the LAN
PIM Hello messages and compares its DR priority and IP address with examines the received PIM Hello messages and compares its own DR
those of its neighbors. The router with the highest DR priority is priority and IP address with those of its neighbors. The router with
the PIM DR. If there are multiple such routers, their IP addresses the highest DR priority is the PIM DR. If there are multiple such
are used as the tie-breaker, as described in [RFC4601]. routers, their IP addresses are used as the tie-breaker, as described
in [RFC7761].
In order to share forwarding load among last hop routers, besides the In order to share forwarding load among last hop routers, besides the
normal PIM DR election, the GDR is also elected on the last hop normal PIM DR election, the GDR is also elected on the last hop
multi-access LAN. There is only one PIM DR on the multi-access LAN, multi-access LAN. There is only one PIM DR on the multi-access LAN,
but there might be multiple GDR Candidates. but there might be multiple GDR Candidates.
For each multicast flow, that is, (*,G) for ASM and (S,G) for SSM, a For each multicast flow, that is, (*,G) for ASM and (S,G) for SSM, a
hash algorithm is used to select one of the routers to be the GDR. A hash algorithm is used to select one of the routers to be the GDR. A
new DR Load Balancing Capability (DRLBC) PIM Hello Option, which new DR Load Balancing Capability (DRLBC) PIM Hello Option, which
contains hash algorithm type, is announced by routers on interfaces contains hash algorithm type, is announced by routers on interfaces
where this specification is enabled. Last hop routers with the new where this specification is enabled. Last hop routers with the new
DRLBC Option advertised in its Hello, and using the same GDR election DRLBC Option advertised in its Hello, and using the same GDR election
hash algorithm and the same DR priority as the PIM DR, are considered hash algorithm and the same DR priority as the PIM DR, are considered
as GDR Candidates. as GDR Candidates.
Hash Masks are defined for Source, Group and RP separately, in order Hash Masks are defined for Source, Group and RP separately, in order
to handle PIM ASM/SSM. The masks, as well as a sorted list of GDR to handle PIM ASM/SSM. The masks, as well as a sorted list of GDR
Candidates' Addresses, are announced by DR in a new DR Load Balancing Candidate Addresses, are announced by the DR in a new DR Load
GDR (DRLBGDR) PIM Hello Option. Balancing GDR (DRLBGDR) PIM Hello Option.
A hash algorithm based on the announced Source, Group, or RP masks A hash algorithm based on the announced Source, Group, or RP masks
allows one GDR to be assigned to a corresponding multicast state. allows one GDR to be assigned to a corresponding multicast state.
And that GDR is responsible for initiating the creation of the And that GDR is responsible for initiating the creation of the
multicast forwarding tree for multicast traffic. multicast forwarding tree for multicast traffic.
4.1. GDR Candidates 4.1. GDR Candidates
GDR is the new concept introduced by this specification. GDR GDR is the new concept introduced by this specification. GDR
Candidates are routers eligible for GDR election on the LAN. To Candidates are routers eligible for GDR election on the LAN. To
skipping to change at page 7, line 29 skipping to change at page 7, line 25
4.2. Hash Mask and Hash Algorithm 4.2. Hash Mask and Hash Algorithm
A Hash Mask is used to extract a number of bits from the A Hash Mask is used to extract a number of bits from the
corresponding IP address field (32 for v4, 128 for v6) and calculate corresponding IP address field (32 for v4, 128 for v6) and calculate
a hash value. A hash value is used to select a GDR from GDR a hash value. A hash value is used to select a GDR from GDR
Candidates advertised by PIM DR. For example, 0.0.255.0 defines a Candidates advertised by PIM DR. For example, 0.0.255.0 defines a
Hash Mask for an IPv4 address that masks the first, the second, and Hash Mask for an IPv4 address that masks the first, the second, and
the fourth octets. the fourth octets.
There are three Hash Masks defined, There are three Hash Masks defined:
o RP Hash Mask o RP Hash Mask
o Source Hash Mask o Source Hash Mask
o Group Hash Mask o Group Hash Mask
The hash masks need to be configured on the PIM routers that can The hash masks need to be configured on the PIM routers that can
potentially become a PIM DR, unless the implementation provides potentially become a PIM DR, unless the implementation provides
default Hash Mask. An implementation SHOULD provide masks with default Hash Mask values. An implementation SHOULD provide masks
default values 255.255.255.255 (IPv4) and with default values 255.255.255.255 (IPv4) and
FFFF:FFFF:FFFF:FFFF:FFFFF:FFFF:FFFF:FFFF (IPv6). FFFF:FFFF:FFFF:FFFF:FFFFF:FFFF:FFFF:FFFF (IPv6).
o If the group is ASM and the RP Hash Mask announced by the PIM DR o If the group is in ASM mode and the RP Hash Mask announced by the
is not 0, calculate the value of hashvalue_RP [Section 4.3] to PIM DR is not 0, calculate the value of hashvalue_RP [Section 4.3]
determine GDR. to determine GDR.
o If the group is ASM and the RP Hash Mask announced by the PIM DR o If the group is in ASM mode and the RP Hash Mask announced by the
is 0, obtain the value of hashvalue_Group [Section 4.3 ] to PIM DR is 0, obtain the value of hashvalue_Group [Section 4.3 ] to
determine GDR. determine GDR.
o If the group is SSM, use hashvalue_SG [Section 4.3] to determine o If the group is in SSM mode, use hashvalue_SG [Section 4.3] to
GDR. determine GDR.
A simple Modulo hash algorithm will be discussed in this document. A simple Modulo hash algorithm is defined in this document. However,
However, to allow another hash algorithms to be used, a 4-bytes "Hash to allow another hash algorithms to be used, a 1-octet "Hash
Algorithm Type" field is included in DRLBC Hello Option to specify Algorithm Type" field is included in DRLBC Hello Option to specify
the hash algorithm used by a last hop router. the hash algorithm used by a last hop router.
If different hash algorithm types are advertised among last hop If different hash algorithm types are advertised among last hop
routers, only last hop routers running the same hash algorithm as the routers, only last hop routers running the same hash algorithm as the
DR (and having the same DR priority as the DR) are eligible for GDR DR (and having the same DR priority as the DR) are eligible for GDR
election. election.
4.3. Modulo Hash Algorithm 4.3. Modulo Hash Algorithm
Modulo hash algorithm is discussed here with a detailed description The Modulo hash algorithm is discussed here with a detailed
on hashvalue_RP. The same algorithm is described in brief for description on hashvalue_RP. The same algorithm is described in
hashvalue_Group using the group address instead of the RP address for brief for hashvalue_Group using the group address instead of the RP
an ASM group with RP_hashmask==0, and also with hashvalue_SG for a address for an ASM group with zero RP_hashmask, and also with
the source address of an (S,G), instead of the RP address, hashvalue_SG for a the source address of an (S,G), instead of the RP
address,
o For ASM groups, with a non-zero RP_Hash Mask, hash value is o For ASM groups, with a non-zero RP_Hash Mask, hash value is
calculated as: calculated as:
hashvalue_RP = (((RP_address & RP_hashmask) >> N) & 0xFFFF) % M hashvalue_RP = (((RP_address & RP_hashmask) >> N) & 0xFFFF) % M
RP_address is the address of the RP defined for the group. N RP_address is the address of the RP defined for the group. N
is the number of zeros, counted from the least significant bit is the number of zeroes, counted from the least significant bit
of the RP_hashmask. M is the number of GDR Candidates. of the RP_hashmask. M is the number of GDR Candidates.
For example, Router X with IPv4 address 203.0.113.1 receives a For example, Router X with IPv4 address 203.0.113.1 receives a
DRLBGDR Hello Option from the DR, which announces RP Hash Mask DRLBGDR Hello Option from the DR, which announces RP Hash Mask
0.0.255.0 and a list of GDR Candidates, sorted by IP addresses 0.0.255.0 and a list of GDR Candidates, sorted by IP addresses
from high to low: 203.0.113.3, 203.0.113.2 and 203.0.113.1. from high to low: 203.0.113.3, 203.0.113.2 and 203.0.113.1.
The ordinal number assigned to those addresses would be: The ordinal number assigned to those addresses would be:
0 for 203.0.113.3; 1 for 203.0.113.2; 2 for 203.0.113.1 (Router 0 for 203.0.113.3; 1 for 203.0.113.2; 2 for 203.0.113.1 (Router
X) X)
skipping to change at page 9, line 10 skipping to change at page 9, line 10
matches the ordinal number assigned to Router X. Router X will matches the ordinal number assigned to Router X. Router X will
be the GDR for Group1, which uses 192.0.2.1 as the RP. be the GDR for Group1, which uses 192.0.2.1 as the RP.
The hashvalue_RP for RP2 198.51.100.2 is: The hashvalue_RP for RP2 198.51.100.2 is:
(((198.51.100.2 & 0.0.255.0) >> 8) & 0xFFFF % 3) = 100 % 3 = 1 (((198.51.100.2 & 0.0.255.0) >> 8) & 0xFFFF % 3) = 100 % 3 = 1
which is different from Router X's ordinal number(2) hence, which is different from Router X's ordinal number(2) hence,
Router X will not be GDR for Group2. Router X will not be GDR for Group2.
o If RP_hashmask is 0, a hash value for ASM group is calculated o If RP_hashmask is 0, a hash value for an ASM group is calculated
using the group Hash Mask: using the Group Hash Mask:
hashvalue_Group = (((Group_address & Group_hashmask) >> N) & hashvalue_Group = (((Group_address & Group_hashmask) >> N) &
0xFFFF) % M 0xFFFF) % M
Compare hashvalue_Group with Ordinal number assigned to Router Compare hashvalue_Group with Ordinal number assigned to Router
X, to decide if Router X is the GDR. X, to decide if Router X is the GDR.
o For SSM groups, a hash value is calculated using both the source o For SSM groups, a hash value is calculated using both the Source
and group Hash Mask: and Group Hash Mask:
hashvalue_SG = ((((Source_address & Source_hashmask) >> N_S) & hashvalue_SG = ((((Source_address & Source_hashmask) >> N_S) &
0xFFFF) ^ (((Group_address & Group_hashmask) >> N_G) & 0xFFFF)) 0xFFFF) ^ (((Group_address & Group_hashmask) >> N_G) & 0xFFFF))
% M % M
4.3.1. Limitations
The Modulo Hash Algorithm has poor failover characteristics when a
shared LAN has more than two GDRs. In the case of more than two GDRs
on a LAN, when one GDR fails, all of the groups may be reassigned to
a new GDR, even if they were not assigned to the failed GDR.
However, many deployments use only two routers on a shared LAN for
redundancy purposes. Future work may define new hash algorithms
where only groups assigned to the failed GDR get reassigned.
4.4. PIM Hello Options 4.4. PIM Hello Options
When a last hop PIM router sends a PIM Hello from an interface with When a last hop PIM router sends a PIM Hello for an interface with
this specification enabled, it includes a new option, called "Load this specification enabled, it includes a new option, called "Load
Balancing Capability (DRLBC)". Balancing Capability (DRLBC)".
Besides this DRLBC Hello Option, the elected PIM DR also includes a Besides this DRLBC Hello Option, the elected PIM DR also includes a
new "DR Load Balancing GDR (DRLBGDR) Hello Option". The DRLBGDR new "DR Load Balancing GDR (DRLBGDR) Hello Option". The DRLBGDR
Hello Option consists of three Hash Masks as defined above and also Hello Option consists of three Hash Masks as defined above and also a
the sorted list of all GDR Candidates' Address on the last hop LAN. sorted list of GDR Candidate addresses on the last hop LAN.
The elected PIM DR uses DRLBC Hello Option advertised by all routers The elected PIM DR uses DRLBC Hello Option advertised by all routers
on the last hop LAN to compose its DRLBGDR. The GDR Candidates use on the last hop LAN to compose the DRLBGDR Option. The GDR
DRLBGDR Hello Option advertised by PIM DR to calculate hash value. Candidates use the DRLBGDR Hello Option advertised by the PIM DR to
calculate the hash value.
5. Hello Option Formats 5. Hello Option Formats
5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option 5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option
0 1 2 3
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
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 = TBD | Length = 4 | | Type = TBD | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hash Algorithm Type | | Reserved | Hash Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Capability Hello Option Figure 3: Capability Hello Option
Type: TBD. Type: TBD
Length: 4 octets Length: 4
Hash Algorithm Type: 0 for Modulo hash algorithm Hash Algorithm Type: 0 for Modulo hash algorithm
This DRLBC Hello Option SHOULD be advertised by last hop routers from This DRLBC Hello Option MUST be advertised by last hop routers on
interfaces with this specification enabled. interfaces with this specification enabled.
5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option 5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option
0 1 2 3 0 1 2 3
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 = TBD | Length | | Type = TBD | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Mask | | Group Mask |
skipping to change at page 10, line 43 skipping to change at page 10, line 48
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Mask | | RP Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GDR Candidate Address(es) | | GDR Candidate Address(es) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: GDR Hello Option Figure 4: GDR Hello Option
Type: TBD Type: TBD
Length: 3 x (4 byte or 16 byte) + n x (4 byte or 16 byte) where n Length: (3 + n) x (4 or 16) where n is the number of GDR
is the number of GDR candidates. candidates.
Group Mask (32/128 bits): Mask Group Mask (32/128 bits): Mask
Source Mask (32/128 bits): Mask Source Mask (32/128 bits): Mask
RP Mask (32/128 bits): Mask RP Mask (32/128 bits): Mask
All masks MUST be in the same address family as the Hello IP All masks MUST be in the same address family as the Hello IP
header. header.
GDR Address (32/128 bits): Address(es) of GDR Candidate(s) GDR Address (32/128 bits): Address(es) of GDR Candidate(s)
All addresses must be in the same address family as the Hello All addresses must be in the same address family as the Hello
IP header. The addresses are sorted in descending order. The IP header. The addresses are sorted in descending order. The
order is converted to the ordinal number associated with each order is converted to the ordinal number associated with each
skipping to change at page 11, line 14 skipping to change at page 11, line 19
RP Mask (32/128 bits): Mask RP Mask (32/128 bits): Mask
All masks MUST be in the same address family as the Hello IP All masks MUST be in the same address family as the Hello IP
header. header.
GDR Address (32/128 bits): Address(es) of GDR Candidate(s) GDR Address (32/128 bits): Address(es) of GDR Candidate(s)
All addresses must be in the same address family as the Hello All addresses must be in the same address family as the Hello
IP header. The addresses are sorted in descending order. The IP header. The addresses are sorted in descending order. The
order is converted to the ordinal number associated with each order is converted to the ordinal number associated with each
GDR candidate in hash value calculation. For example, GDR candidate in hash value calculation. For example, if
addresses advertised are R3, R2, R1, the ordinal number addresses advertised are R3, R2, R1, the ordinal number
assigned to R3 is 0, to R2 is 1 and to R1 is 2. assigned to R3 is 0, to R2 is 1 and to R1 is 2.
If "Interface ID" option, as described in [RFC6395], presents If the "Interface ID" option, as specified in [RFC6395], is
in a GDR Candidate's PIM Hello message, and the "Router ID" present in a GDR Candidate's PIM Hello message, and the "Router
portion is non-zero, ID" portion is non-zero:
+ For IPv4, the "GDR Candidate Address" will be set directly + For IPv4, the "GDR Candidate Address" will be set directly
to "Router ID". to the "Router ID".
+ For IPv6, the "GDR Candidate Address" will be set to the + For IPv6, the "GDR Candidate Address" will be set to the
IPv4-IPv6 translated address of "Router ID", as described in IPv4-IPv6 translated address of the "Router ID", as
[RFC4291] , that is the "Router-ID" is appended to the described in [RFC4291], that is the "Router-ID" is appended
prefix of 96-bits zeros. to the prefix of 96 bits of zeroes.
If the "Interface ID" option is not present in a GDR If the "Interface ID" option is not present in a GDR
Candidate's PIM Hello message, or if the "Interface ID" option Candidate's PIM Hello message, or if the "Interface ID" option
is present but the "Router ID" field is zero, the "GDR is present but the "Router ID" field is zero, the "GDR
Candidate Address" will be the IPv4 or IPv6 source address from Candidate Address" will be the IPv4 or IPv6 source address of
PIM Hello message. the PIM Hello message.
This DRLBGDR Hello Option MUST only be advertised by the This DRLBGDR Hello Option MUST only be advertised by the
elected PIM DR. elected PIM DR.
6. Protocol Specification 6. Protocol Specification
6.1. PIM DR Operation 6.1. PIM DR Operation
The DR election process is still the same as defined in [RFC4601]. A The DR election process is still the same as defined in [RFC7761]. A
DR that has this specification enabled on the interface advertises DR that has this specification enabled on an interface advertises the
the new DRLBGDR Hello Option, which contains value of masks from user new DRLBGDR Hello Option, which contains mask values from user
configuration, followed by a sorted list of all GDR Candidates' configuration, followed by a sorted list of GDR Candidate Addresses,
Addresses, from the highest value to the lowest value. Moreover, from the highest value to the lowest value. Moreover, same as non-DR
same as non-DR routers, DR also advertises DRLBC Hello Option to routers, the DR also advertises DRLBC Hello Option to indicate its
indicate its capability of supporting this specification and the type capability of supporting this specification and the type of its GDR
of its GDR election hash algorithm. election hash algorithm.
If a PIM DR receives a PIM Hello with DRLBGDR Option, the PIM DR If a PIM DR receives a PIM Hello with the DRLBGDR Option, the PIM DR
SHOULD ignore the TLV. SHOULD ignore the TLV.
If a PIM DR receives a neighbor DRLBC Hello Option, which contains If a PIM DR receives a neighbor DRLBC Hello Option, which contains
the same hash algorithm type as the DR, and the neighbor has the same the same hash algorithm type as the DR, and the neighbor has the same
DR priority as the DR, PIM DR SHOULD consider the neighbor as a GDR DR priority as the DR, PIM DR SHOULD consider the neighbor as a GDR
Candidate and insert the GDR Candidate's Address into the sorted list Candidate and insert the GDR Candidate's Address into the sorted list
of DRLBGDR Option. of the DRLBGDR Option. However, the DR MAY have policies limiting
which GDR Candidates, or the number of GDR Candidates to include.
6.2. PIM GDR Candidate Operation 6.2. PIM GDR Candidate Operation
When an IGMP/MLD join is received, without this specification, only When an IGMP/MLD report is received, without this specification, only
PIM DR will handle the join and potentially run into the issues the PIM DR will handle the join and potentially run into the issues
described earlier. Using this specification, a hash algorithm is described earlier. Using this specification, a hash algorithm is
used on GDR Candidate to determine which router is going to be used by the GDR Candidates to determine which router is going to be
responsible for building forwarding trees on behalf of the host. responsible for building forwarding trees on behalf of the host.
If a router supports this specification then each of the interfaces If this specification is enabled on an interface, the router MUST
where multicast protocol is enabled, it MUST advertise DRLBC Hello include the DRLBC Hello Option in its PIM Hello on the interface.
Option in its PIM Hello. Though DRLBC option in PIM hello does not Note that the presence of the DRLBC Option in PIM Hello does not
guarantee that this router would be considered as a GDR candidate. guarantee that this router would be considered as a GDR candidate.
For example, this router may have lower priority configured on shared Once DR election is done, the DRLBGDR Hello Option would be received
LAN compare to other PIM routers. Once DR election is done, DRLBGDR from the current PIM DR on the link which would contain a list of
Hello option would be received from the current PIM DR on the link GDRs selected by the PIM DR.
which would contain list of GDR.
A GDR Candidate may receive a DRLBGDR Hello Option from PIM DR with A router only acts as a GDR candidate if it is included in the GDR
different Hash Masks from those configured on it. The GDR Candidate list of the DRLBGDR Hello Option.
must use the Hash Masks advertised by the PIM DR to calculate the
hash value.
A GDR Candidate may receive a DRLBGDR Hello Option from a PIM router A GDR Candidate may receive a DRLBGDR Hello Option from the PIM DR
which is not DR. The GDR Candidate MUST ignore such DRLBGDR Hello with different Hash Masks from those the candidate was configured
Option. with. The GDR Candidate MUST use the Hash Masks advertised by the
PIM DR to calculate the hash value.
A GDR Candidate may receive a Hello from the elected PIM DR, and the A GDR Candidate MUST ignore the DRLBGDR Hello Option if it is
PIM DR does not support this specification. The GDR election received from a PIM router which is not the DR.
described by this specification will not take place, that is only the
PIM DR joins the multicast tree.
A router only acts as GDR if it is included in the GDR list of If the PIM DR does not support this specification, GDR election will
DRLBGDR Hello Option not take place, and only the PIM DR joins the multicast tree.
6.2.1. Router Receives New DRLBGDR 6.2.1. Router Receives New DRLBGDR
When a router receives a new DRLBGDR from the current PIM DR, it need The first time a router receives a DRLBGDR option from the PIM DR, it
to process and check if router is in list of of GDR MUST process the option and check if it is in the GDR list.
1. If a router is not listed as a GDR candidate in DRLBGDR, no 1. If a router is not listed as a GDR candidate in DRLBGDR, no
action is needed. action is needed.
2. If a router is listed as a GDR candidate in DRLBGDR, then it need 2. If a router is listed as a GDR candidate in DRLBGDR, then it MUST
to process each of the groups in the IGMP/MLD reports. The masks process each of the groups, or source and group pairs if SSM, in
are announced in the PIM Hello by DR as DRLBGDR Hello option. the IGMP/MLD reports. The masks are announced in the PIM Hello
For each of groups in the reports it (PIM Router) needs to run by the DR in the DRLBGDR Hello Option. For each group in the
hash algorithm (described in section 4.3) based on the announced reports that is in ASM mode, and each source and group pair if
Source, Group or RP masks to determine if it is GDR for specified the group is in SSM mode, it (PIM Router) needs to run the hash
group. If the hash result is to be the GDR for the multicast algorithm (described in section 4.3) based on the announced
flow, it does build the multicast forwarding tree. If it is not Source, Group or RP masks to determine if it is the GDR for
the GDR for the multicast flow, no action is needed. specified group, or source and group pair. If the hash result is
to be the GDR for the multicast flow, it does build the multicast
forwarding tree. If it is not the GDR for the multicast flow, no
action is needed.
6.2.2. Router Receives Updated DRLBGDR 6.2.2. Router Receives Updated DRLBGDR
If a router (GDR or non GDR) receives an unchanged DRLBGDR from the If a router (GDR or non GDR) receives an unchanged DRLBGDR from the
current PIM DR, no action is needed. current PIM DR, no action is needed.
If a router (GDR or non GDR) receives a new or modified DRLBGDR from If a router (GDR or non GDR) receives a new or modified DRLBGDR from
the current PIM DR. It requires processing as described below: the current PIM DR, it requires processing as described below:
1. If it was GDR and still included in current GDR list: it needs to 1. If it was included in the previous GDR list, and still is
process each of the groups and run the hash algorithm to check if included in the new GDR list: It needs to process each of the
it is still the GDR for the given group. groups, or source and group pairs if the group is in SSM mode,
and run the hash algorithm to check if it is still the GDR for
the given group, or source and group pair if SSM.
If it was the GDR for group G and the new hash result chose it If it was the GDR for a group, or source and group pair if
as the GDR, then no processing is required. SSM, and the new hash result chose it as the GDR, then no
processing is required.
If it was the GDR for a group earlier and now it is no longer If it was the GDR for a group, or source and group pair if
the GDR, then it sets its assert metric for the multicast flow SSM, earlier and now it is no longer the GDR, then it sets its
to be (PIM_ASSERT_INFINITY - 1), as explained in Sec 6.3 assert metric for the multicast flow to be
(PIM_ASSERT_INFINITY - 1), as explained in Section 6.3.
If it was not the GDR for a group earlier, than even the new If it was not the GDR for a group, or source and group pair if
hash does not make it GDR. For the multicast group no SSM, earlier, and the new hash does not make it GDR, then no
processing is required. processing is required.
If it was not the GDR for an earlier group and now becomes the If it was not the GDR for an earlier group, or source and
GDR, it starts building multicast forwarding tree for this group pair if SSM, and now becomes the GDR, it starts building
flow. multicast forwarding tree for this flow.
2. If it was not the GDR , and updated DRLBGDR from current PIM DR 2. If it was included in the previous GDR list, but is not included
contains this router as one of the GDR. In this case this router in the new GDR list: It needs to process each of the groups, or
being new GDR candidate MUST run hash algorithm for each of the source and group pairs if the group is in SSM mode.
groups (multicast flows) and for given group,
If it is not the GDR, no processing is required. If it was the GDR for a group, or source and group pair if
SSM, it sets its assert metric for the multicast flow to be
(PIM_ASSERT_INFINITY - 1), as explained in Section 6.3.
If it is hashed as the GDR , it needs to build multicast If it was not the GDR, then no processing is required.
3. If it was not included in the previous GDR list, but is included
in the new GDR list, the router MUST run the hash algorithm for
each of the groups, source and group pairs if SSM.
If it is not the GDR for a group, or source and group pair if
SSM, no processing is required.
If it is hashed as the GDR, it needs to build a multicast
forwarding tree. forwarding tree.
6.3. PIM Assert Modification 6.3. PIM Assert Modification
It is possible that the identity of the GDR might change in the It is possible that the identity of the GDR might change in the
middle of an active flow. Examples this could happen include: middle of an active flow. Examples when this could happen include:
When a new PIM router comes up When a new PIM router comes up
When a GDR restarts When a GDR restarts
When the GDR changes, existing traffic might be disrupted. When the GDR changes, existing traffic might be disrupted.
Duplicates or packet losses might be observed. To illustrate the Duplicates or packet loss might be observed. To illustrate the case,
case, consider the following scenario where there are two streams G1 consider the following scenario where there are two flows G1 and G2.
and G2. R1 is the GDR for G1, and R2 is the GDR for G2. When R3 R1 is the GDR for G1, and R2 is the GDR for G2. When R3 comes up
comes up online, it is possible that R3 becomes GDR for both G1 and online, it is possible that R3 becomes GDR for both G1 and G2, hence
G2, hence R3 starts to build the forwarding tree for G1 and G2. If R3 starts to build the forwarding tree for G1 and G2. If R1 and R2
R1 and R2 stop forwarding before R3 completes the process, packet stop forwarding before R3 completes the process, packet loss might
loss might occur. On the other hand, if R1 and R2 continue occur. On the other hand, if R1 and R2 continue forwarding while R3
forwarding while R3 is building the forwarding trees, duplicates is building the forwarding trees, duplicates might occur.
might occur.
This is not a typical deployment scenario but might still happen. This is not a typical deployment scenario but might still happen.
Here we describe a mechanism to minimize the impact. We essentially Here we describe a mechanism to minimize the impact. We essentially
want to minimize packet loss. Therefore, we would allow a small want to minimize packet loss. Therefore, we would allow a small
amount of duplicates and depend on PIM Assert to minimize the amount of duplicates and depend on PIM Assert to minimize the
duplication. duplication.
When the role of GDR changes as above, instead of immediately When the role of GDR changes as above, instead of immediately
stopping forwarding, R1 and R2 continue forwarding to G1 and G2 stopping forwarding, R1 and R2 continue forwarding to G1 and G2
respectively, while, at the same time, R3 build forwarding trees for respectively, while, at the same time, R3 build forwarding trees for
skipping to change at page 15, line 10 skipping to change at page 15, line 24
(PIM_ASSERT_INFINITY - 1). (PIM_ASSERT_INFINITY - 1).
Using the above example, for G1, assume R1 and R3 agree on the new Using the above example, for G1, assume R1 and R3 agree on the new
GDR, which is R3. R1 will set its Assert metric as GDR, which is R3. R1 will set its Assert metric as
(PIM_ASSERT_INFINITY - 1). That will make R3, which has normal (PIM_ASSERT_INFINITY - 1). That will make R3, which has normal
metric in its Assert as the Assert winner. metric in its Assert as the Assert winner.
For G2, assume it takes a slightly longer time for R2 to find out For G2, assume it takes a slightly longer time for R2 to find out
that R3 is the new GDR and still considers itself being the GDR while that R3 is the new GDR and still considers itself being the GDR while
R3 already has assumed the role of GDR. Since both R2 and R3 think R3 already has assumed the role of GDR. Since both R2 and R3 think
they are GDRs, they further compare the metric and IP address. If R3 they are GDRs, they further compare their metric and IP addresses.
has the better routing metric, or the same metric but a better tie- If R3 has the better routing metric, or the same metric but a better
breaker, the result will be consistent during GDR selection. If tie-breaker, the result will be consistent during GDR selection. If
unfortunately, R2 has the better metric or the same metric but a unfortunately, R2 has the better metric or the same metric but a
better tie-breaker, R2 will become the Assert winner and continues to better tie-breaker, R2 will become the Assert winner and continues to
forward traffic. This will continue until: forward traffic. This will continue until:
The next PIM Hello option from DR selects R3 as the GDR. R3 will The next PIM Hello Option from DR selects R3 as the GDR. R3 will
then build the forwarding tree and send an Assert. then build the forwarding tree and send an Assert.
The process continues until R2 agrees to the selection of R3 as the The process continues until R2 agrees to the selection of R3 as the
GDR, and set its own Assert metric to (PIM_ASSERT_INFINITY - 1), GDR, and sets its own Assert metric to (PIM_ASSERT_INFINITY - 1),
which will make R3 the Assert winner. During the process, we will which will make R3 the Assert winner. During the process, we will
see intermittent duplication of traffic but packet loss will be see intermittent duplication of traffic but packet loss will be
minimized. In the unlikely case that R2 never relinquishes its role minimized. In the unlikely case that R2 never relinquishes its role
as GDR (while every other router thinks otherwise), the proposed as GDR (while every other router thinks otherwise), the proposed
mechanism also helps to keep the duplication to a minimum until mechanism also helps to keep the duplication to a minimum until
manual intervention takes place to remedy the situation. manual intervention takes place to remedy the situation.
7. Compatibility 7. Compatibility
In case of the hybrid Ethernet shared LAN ( where some PIM router In the case of a hybrid Ethernet shared LAN (where some PIM routers
enables specification defined in this draft and some do not enable) enable the specification defined in this document, and some do not)
o If a router which does not support specification defined in this o If a router which does not support this specification becomes the
draft becomes DR on link, it MUST be only DR on link as [RFC4601] DR on the LAN, then it is the only router acting as a DR, and
and there would be no router which would act as GDR. there will be no load-balancing.
o If a router which does not support specification defined in this o If a router which does not support this specification becomes a
draft becomes non DR on link, then it should act as non-DR defined non-DR on link, then it acts as non-DR defined in [RFC7761], and
in [RFC4601]. it will not take part in any load-balancing.
8. Manageability Considerations 8. Manageability Considerations
o All of the routers in LAN that support this specification MUST use Only the routers announcing the same Hash Algorithm as the DR would
identical Hash Algorithm Type (described in section 5.1). In the be considered as GDR candidates. Network administrators need to make
case of a hybrid Hash Algorithm Type, one MUST go backward to use sure that the desired set of routers announce the same algorithm.
DR election method defined in PIM-SM [RFC4601]. Migration between Migration between different algorithm types is not considered in this
different algorithm type is out of the scope of this document. document.
9. IANA Considerations 9. IANA Considerations
IANA has temporarily assigned type 34 for the PIM DR Load Balancing IANA has temporarily assigned type 34 for the PIM DR Load Balancing
Capability (DRLBC) Hello Option, and type 35 for the PIM DR Load Capability (DRLBC) Hello Option, and type 35 for the PIM DR Load
Balancing GDR (DRLBGDR) Hello Option. IANA is requested to make Balancing GDR (DRLBGDR) Hello Option. IANA is requested to make
these assignments permanent when this document is published as an these assignments permanent when this document is published as an
RFC. The string TBD should be replaced by the assigned values RFC. The string TBD should be replaced by the assigned values
accordingly. accordingly. This document requests IANA to create a DRLB hash type
registry. This should be placed in the "Protocol Independent
Multicast (PIM)" branch of the tree.
9.1. Initial registry
The initial content of the registry should be as follows.
Type Name Reference
------ ---------------------------------------- --------------------
0 Hash algorithm modulo This document
1-255 Unassigned
9.2. Assignment of new message types
Assignment of new message types is done according to the "IETF
Review" model, see [RFC5226].
10. Security Considerations 10. Security Considerations
Security of the new DR Load Balancing PIM Hello Options is only Security of the new DR Load Balancing PIM Hello Options is only
guaranteed by the security of PIM Hello message, so the security guaranteed by the security of PIM Hello messages, so the security
considerations for PIM Hello messages as described in PIM-SM considerations for PIM Hello messages as described in PIM-SM
[RFC4601] apply here. [RFC7761] apply here.
11. Acknowledgement 11. Acknowledgement
The authors would like to thank Steve Simlo, Taki Millonis for The authors would like to thank Steve Simlo, Taki Millonis for
helping with the original idea, Bill Atwood, Bharat Joshi for review helping with the original idea, Bill Atwood, Bharat Joshi for review
comments, Toerless Eckert and Rishabh Parekh for helpful conversation comments, Toerless Eckert and Rishabh Parekh for helpful conversation
on the document. on the document.
Special thanks to Anish Kachinthaya, Anvitha Kachinthaya and Jake Special thanks to Anish Kachinthaya, Anvitha Kachinthaya and Jake
Holland for reviewing the document and providing comments. Holland for reviewing the document and providing comments.
skipping to change at page 16, line 44 skipping to change at page 17, line 28
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>. 2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<https://www.rfc-editor.org/info/rfc4601>.
[RFC6395] Gulrajani, S. and S. Venaas, "An Interface Identifier (ID) [RFC6395] Gulrajani, S. and S. Venaas, "An Interface Identifier (ID)
Hello Option for PIM", RFC 6395, DOI 10.17487/RFC6395, Hello Option for PIM", RFC 6395, DOI 10.17487/RFC6395,
October 2011, <https://www.rfc-editor.org/info/rfc6395>. October 2011, <https://www.rfc-editor.org/info/rfc6395>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
12.2. Informative References 12.2. Informative References
[HELLO-OPT] [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA, "PIM Hello Options", IANA PIM-HELLO-OPTIONS, March IANA Considerations Section in RFCs", RFC 5226,
2007. DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
Authors' Addresses Authors' Addresses
Yiqun Cai Yiqun Cai
Alibaba Group Alibaba Group
Email: yiqun.cai@alibaba-inc.com Email: yiqun.cai@alibaba-inc.com
Heidi Ou Heidi Ou
Alibaba Group Alibaba Group
Sri Vallepalli Sri Vallepalli
Cisco Systems Cisco Systems, Inc.
3625 Cisco Way, 3625 Cisco Way
Sanjose, CALIFORNIA 95134 San Jose CA 95134
UNITED STATES USA
Email: svallepa@cisco.com Email: svallepa@cisco.com
Mankamana Mishra Mankamana Mishra
Cisco Systems Cisco Systems, Inc.
821 Alder Drive, 821 Alder Drive,
MILPITAS, CALIFORNIA 95035 Milpitas CA 95035
UNITED STATES USA
Email: mankamis@cisco.com Email: mankamis@cisco.com
Stig Venaas Stig Venaas
Cisco Systems Cisco Systems, Inc.
821 Alder Drive, Tasman Drive
MILPITAS, CALIFORNIA 95035 San Jose CA 95134
UNITED STATES USA
Email: stig@cisco.com Email: stig@cisco.com
Andy Green Andy Green
British Telecom British Telecom
Adastral Park Adastral Park
Ipswich IP5 2RE Ipswich IP5 2RE
United Kingdom United Kingdom
Email: andy.da.green@bt.com Email: andy.da.green@bt.com
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