draft-ietf-pim-drlb-07.txt   draft-ietf-pim-drlb-08.txt 
Network Working Group Yiqun. Cai Network Working Group Yiqun. Cai
Internet-Draft Heidi. Ou Internet-Draft Heidi. Ou
Intended status: Standards Track Alibaba Group Intended status: Standards Track Alibaba Group
Expires: July 20, 2018 Sri. Vallepalli Expires: December 21, 2018 Sri. Vallepalli
Mankamana. Mishra Mankamana. Mishra
Stig. Venaas Stig. Venaas
Cisco Systems Cisco Systems
Andy. Green Andy. Green
British Telecom British Telecom
January 16, 2018 June 19, 2018
PIM Designated Router Load Balancing PIM Designated Router Load Balancing
draft-ietf-pim-drlb-07 draft-ietf-pim-drlb-08
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. In
this document, we propose a modification to the PIM-SM protocol that this document, we propose a modification to the PIM-SM protocol that
allows more than one of these last hop routers to be selected so that allows more than one of these last hop routers to be selected so that
the forwarding load can be distributed among these routers. the forwarding load can be distributed among these routers.
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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 July 20, 2018. This Internet-Draft will expire on December 21, 2018.
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 21 skipping to change at page 2, line 21
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . . . . . . 7 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
4.4. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 9 4.4. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 9
5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . 10 5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . 9
5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 10 5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 9
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 . . . . . . . . . . . . . . . . . . . . 12 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 . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 17 12.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
skipping to change at page 3, line 27 skipping to change at page 3, line 27
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 [RFC4601], 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
proves 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). The forwarding load of a last hop LAN packets due to RPF failures). Hence the forwarding load of a last
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. These days, it is very common that the this particular interface. It is very common that the last hop LAN
last hop LAN usually consists of switches that run IGMP/MLD or PIM usually consists of switches that run IGMP/MLD or PIM snooping. This
snooping. This allows the forwarding of multicast packets to be allows the forwarding of multicast packets to be restricted only to
restricted only to segments leading to receivers who have indicated segments leading to receivers who have indicated their interest in
their interest in multicast groups using either IGMP or MLD. The multicast groups using either IGMP or MLD. The emergence of the
emergence of the switched Ethernet allows the aggregated bandwidth to switched Ethernet allows the aggregated bandwidth to exceed,
exceed, some times by a large number, that of a single link. For sometimes by a large number, that of a single link. For example, let
example, let us modify Figure 1 and introduce an Ethernet switch in us modify Figure 1 and introduce an Ethernet switch in Figure 2.
Figure 2.
( core networks ) ( core networks )
| | | | | |
| | | | | |
R1 R2 R3 R1 R2 R3
| | | | | |
+=gi0===gi1===gi2=+ +=gi0===gi1===gi2=+
+ + + +
+ switch + + switch +
+ + + +
skipping to change at page 4, line 25 skipping to change at page 4, line 25
| | | | | |
H1 H2 H3 H1 H2 H3
Figure 2: Last Hop Network with Ethernet Switch Figure 2: Last Hop Network with Ethernet Switch
Let us assume that each individual link is a Gigabit Ethernet. Each Let us assume that each individual link is a Gigabit Ethernet. Each
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
data and different traffic is requested by each host. This unique multicast data. This totals to 1.5 Gbps of data, which is
represents a total 1.5 Gbps of data, which is under what each switch less than what each switch or the combined uplink bandwidth across
or the combined uplink bandwidth across the routers can handle, even the routers can handle, even under failure of a single router.
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 router, the only handle a throughput of 1Gbps. And if R1 is the only DR (the PIM
PIM DR elected using the procedure defined by [RFC4601], at least 500 DR elected using the procedure defined by [RFC4601]) 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 The problem may also manifest itself in a different way. For
example, R1 happens to forward 500 Mbps worth of unicast data to H1, example, R1 happens to forward 500 Mbps worth of unicast data to H1,
and at the same time, H2 and H3 each requests 300 Mbps of different and at the same time, H2 and H3 each request 300 Mbps of different
multicast data. Once again packet drop happens on R1 while in the multicast data. R1 experiences packet drop once again. while, in the
mean time, there is sufficient forwarding capacity left on R2 and R3 meantime, there is sufficient forwarding capacity left on R2 and R3
and link capacity between the switch and R2/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, in the event of a forwarder on the last hop router for shared LAN, when R1 goes out of
failure when R1 goes out of service, multicast forwarding for the service, multicast forwarding for the entire LAN has to be rebuilt by
entire LAN has to be rebuilt by the newly elected PIM DR. However, the newly elected PIM DR. However, if there was a way that allowed
if there was a way that allowed multiple routers to forward to the multiple routers to forward to the LAN for different groups, failure
LAN for different groups, failure of one of the routers would only of one of the routers would only lead to disruption to a subset of
lead to disruption to a subset of the flows, therefore improving the the flows, therefore improving the overall resilience of the network.
overall resilience of the network.
There is limitation in the hash algorithm used in this document, but
this draft provides the option to have different and more consistent
hash algorithms in the future.
In this document, we propose a modification to the PIM-SM protocol In this document, we propose a modification to the PIM-SM protocol
that allows more than one of these routers, called Group Designated that allows more than one of these routers, called Group Designated
Router (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 [RFC4601].
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 for the corresponding multicast flow. tree building process for the corresponding multicast flow.
o GDR Candidate: a last hop router that has potential to become a o GDR Candidate: a last hop router that has the potential to become
GDR. A GDR Candidate must have the same DR priority and must run a GDR. A GDR Candidate must have the same DR priority and must
the same GDR election hash algorithm as the DR router. It must run the same GDR election hash algorithm as the DR router. It
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 proposed change described in this specification applies to PIM-SM
last hop routers only. last hop routers only.
It does not alter the behavior of a PIM DR on the first hop network It does not alter the behavior of a PIM DR on the first hop network.
This is because the source tree is built using the IP address of the This is because the source tree is built using the IP address of the
sender, not the IP address of the PIM DR that sends the registers sender, not the IP address of the PIM DR that sends the registers
towards the RP. The load balancing between first hop routers can be towards the RP. The load balancing between first hop routers can be
achieved naturally if an IGP provides equal cost multiple paths achieved naturally if an IGP provides equal cost multiple paths
(which it usually does in practice). And distributing the load to do (which it usually does in practice). Also distributing the load to
registering does not justify the additional complexity required to do registering does not justify the additional complexity required to
support it. support it.
4. Functional Overview 4. Functional Overview
In the existing PIM DR election, when multiple last hop routers are In the existing PIM DR election, when multiple last hop routers are
connected to a multi-access LAN (for example, an Ethernet), one of connected to a multi-access LAN (for example, an Ethernet), one of
them is selected to act as PIM DR. The PIM DR is responsible for them is selected to act as PIM DR. The PIM DR is responsible for
sending local Join/Prune messages towards the RP or source. To elect sending local Join/Prune messages towards the RP or source. In order
the PIM DR, each PIM router on the LAN examines the received PIM to elect the PIM DR, each PIM router on the LAN examines the received
Hello messages and compares its DR priority and IP address with those PIM Hello messages and compares its DR priority and IP address with
of its neighbors. The router with the highest DR priority is the PIM those of its neighbors. The router with the highest DR priority is
DR. If there are multiple such routers, their IP addresses are used the PIM DR. If there are multiple such routers, their IP addresses
as the tie-breaker, as described in [RFC4601]. are used as the tie-breaker, as described in [RFC4601].
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 Candidates' Addresses, are announced by DR in a new DR Load Balancing
GDR (DRLBGDR) PIM Hello Option. GDR (DRLBGDR) PIM Hello Option.
For each multicast flow, a hash algorithm is used to select one of A hash algorithm based on the announced Source, Group, or RP masks
the routers to be the GDR. The masks are announced in PIM Hello by
DR as a DR Load Balancing GDR (DRLBGDR) Hello Option. Besides that,
a DR Load Balancing Capability (DRLBC) Hello Option, which contains
hash algorithm type, is also announced by the router on interfaces
where this specification is enabled. Last hop routers with the new
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
as GDR Candidates.
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
become a GDR Candidate, a router MUST support this specification, become a GDR Candidate, a router MUST support this specification,
have the same DR priority and run the same GDR election hash have the same DR priority and run the same GDR election hash
algorithm as the DR on the LAN. algorithm as the DR on the LAN.
For example, assume there are 4 routers on the LAN: R1, R2, R3 and For example, assume there are 4 routers on the LAN: R1, R2, R3 and
R4, which all support this specification on the LAN. R1, R2 and R3 R4, which all support this specification. R1, R2 and R3 have the
have the same DR priority while R4's DR priority is less preferred. same DR priority while R4's DR priority is less preferred. In this
In this example, R4 will not be eligible for GDR election, because R4 example, R4 will not be eligible for GDR election, because R4 will
will not become a PIM DR unless all of R1, R2 and R3 go out of not become a PIM DR unless all of R1, R2 and R3 go out of service.
service.
Further assume router R1 wins the PIM DR election, and R1, R2 run the Furthermore, assume router R1 wins the PIM DR election, R1 and R2 run
same hash algorithm for GDR election, while R3 runs a different one. the same hash algorithm for GDR election, while R3 runs a different
Then only R1 and R2 will be eligible for GDR election, R3 will not. one. In this case, only R1 and R2 will be eligible for GDR election,
while R3 will not.
As a DR, R1 will include its own Load Balancing Hash Masks, and also As a DR, R1 will include its own Load Balancing Hash Masks and the
the identity of R1 and R2 (the GDR Candidates) in its DRLBGDR Hello identity of R1 and R2 (the GDR Candidates) in its DRLBGDR Hello
Option. Option.
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 hask 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. An implementation SHOULD provide masks with
default values 255.255.255.255 (IPv4) and 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 if the RP Hash Mask announced by the PIM o If the group is ASM and the RP Hash Mask announced by the PIM DR
DR is not 0, calculate the value of hashvalue_RP [Section 4.3] to is not 0, calculate the value of hashvalue_RP [Section 4.3] to
determine GDR. determine GDR.
o If the group is ASM and if the RP Hash Mask announced by the PIM o If the group is ASM and the RP Hash Mask announced by the PIM DR
DR is 0, obtain the value of hashvalue_Group [Section 4.3 ] to 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 SSM, use hashvalue_SG [Section 4.3] to determine
GDR. GDR.
A simple Modulo hash algorithm will be discussed in this document. A simple Modulo hash algorithm will be discussed in this document.
However, to allow other hash algorithm to be used, a 4-bytes "Hash However, to allow another hash algorithms to be used, a 4-bytes "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 as an example, with detailed Modulo hash algorithm is discussed here with a detailed description
description on hashvalue_RP. on hashvalue_RP. The same algorithm is described in brief for
hashvalue_Group using the group address instead of the RP address for
an ASM group with RP_hashmask==0, and also with 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 zeros, 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)
Assume there are 2 RPs: RP1 192.0.2.1 for Group1 and RP2 Assume there are 2 RPs: RP1 192.0.2.1 for Group1 and RP2
198.51.100.2 for Group2. Following the modulo hash algorithm: 198.51.100.2 for Group2. Following the modulo hash algorithm:
N is 8 for 0.0.255.0, and M is 3 for the total number of GDR N is 8 for 0.0.255.0, and M is 3 for the total number of GDR
Candidates. The hashvalue_RP for RP1 192.0.2.1 is: Candidates. The hashvalue_RP for RP1 192.0.2.1 is:
(((192.0.2.1 & 0.0.255.0) >> 8) & 0xFFFF % 3) = 2 % 3 = 2 (((192.0.2.1 & 0.0.255.0) >> 8) & 0xFFFF % 3) = 2 % 3 = 2
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 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
4.4. 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 from 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
the sorted list of all GDR Candidates' Address on the last hop LAN. the sorted list of all GDR Candidates' Address 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 its DRLBGDR. The GDR Candidates use
DRLBGDR Hello Option advertised by PIM DR to calculate hash value. DRLBGDR Hello Option advertised by PIM DR to calculate 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
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 = 4 | | Type = TBD | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hash Algorithm Type | | Hash Algorithm Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Capability Hello Option Figure 3: Capability Hello Option
skipping to change at page 10, line 49 skipping to change at page 10, line 44
| 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 x (4 byte or 16 byte) + n x (4 byte or 16 byte) where n
is number of GDR candidate is the number of GDR 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 from high to low. 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,
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 "Interface ID" option, as described in [RFC6395], presents
in a GDR Candicate's PIM Hello message, and the "Router ID" in a GDR Candidate's PIM Hello message, and the "Router ID"
portion is non-zero, 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 "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 "Router ID", as described in
[RFC4291] , that is the "Router-ID" is appended to the [RFC4291] , that is the "Router-ID" is appended to the
prefix of 96-bits zeros. prefix of 96-bits zeros.
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"Router ID" field is zero, the "GDR Candidate is present but the "Router ID" field is zero, the "GDR
Address" will be the IPv4 or IPv6 source address from PIM Hello Candidate Address" will be the IPv4 or IPv6 source address from
message. PIM Hello message.
This DRLBGDR Hello Option SHOULD 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 [RFC4601]. A
DR that has this specification enabled on the interface, advertises DR that has this specification enabled on the interface advertises
the new LBGRD Hello Option, which contains value of masks from user the new DRLBGDR Hello Option, which contains value of masks from user
configuration, followed by a sorted list of all GDR Candidates' configuration, followed by a sorted list of all GDR Candidates'
Addresses, from high to low. Moreover, same as non-DR routers, DR Addresses, from the highest value to the lowest value. Moreover,
also advertises DRLBC Hello Option to indicate its capability of same as non-DR routers, DR also advertises DRLBC Hello Option to
supporting this specification and the type of its GDR election hash indicate its capability of supporting this specification and the type
algorithm. of its GDR election hash algorithm.
If a PIM DR receives a PIM Hello with DRLBGRD Option, the PIM DR If a PIM DR receives a PIM Hello with 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 DRLBGRD Option. of DRLBGDR Option.
6.2. PIM GDR Candidate Operation 6.2. PIM GDR Candidate Operation
When an IGMP/MLD join is received, without this proposal, only PIM DR When an IGMP/MLD join is received, without this specification, only
will handle the join and potentially run into the issues described PIM DR will handle the join and potentially run into the issues
earlier. Using this proposal, a hash algorithm is used on GDR described earlier. Using this specification, a hash algorithm is
Candidate to determine which router is going to be responsible for used on GDR Candidate to determine which router is going to be
building forwarding trees on behalf of the host. responsible for building forwarding trees on behalf of the host.
A router which supports this specification, a interface where this If a router supports this specification then each of the interfaces
protocol is enabled advertises DRLBC Hello Option in its PIM Hello, where multicast protocol is enabled, it MUST advertise DRLBC Hello
even if the router may not be considered as a GDR Candidate, for Option in its PIM Hello. Though DRLBC option in PIM hello does not
example, due to low DR priority. once DR election is done, DRLBGDR guarantee that this router would be considered as a GDR candidate.
Hello option would be received from the current PIM DR on link. For example, this router may have lower priority configured on shared
LAN compare to other PIM routers. Once DR election is done, DRLBGDR
Hello option would be received from the current PIM DR on the link
which would contain list of GDR.
A GDR Candidate may receive a DRLBGDR Hello Option from PIM DR, with A GDR Candidate may receive a DRLBGDR Hello Option from PIM DR with
different Hash Masks from those configured on it, The GDR Candidate different Hash Masks from those configured on it. The GDR Candidate
must use the Hash Masks advertised by the PIM DR to calculate the must use the Hash Masks advertised by the PIM DR to calculate the
hash value. 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 a PIM router
which is not DR. The GDR Candidate MUST ignore such DRLBGDR Hello which is not DR. The GDR Candidate MUST ignore such DRLBGDR Hello
Option. Option.
A GDR Candidate may receive a Hello from the elected PIM DR, and the A GDR Candidate may receive a Hello from the elected PIM DR, and the
PIM DR does not support this specification. The GDR election PIM DR does not support this specification. The GDR election
described by this specification will not take place, that is only the described by this specification will not take place, that is only the
PIM DR joins the multicast tree. PIM DR joins the multicast tree.
A router only act as GDR if it is included in the GDR list of DRLBGDR A router only acts as GDR if it is included in the GDR list of
Hello Option DRLBGDR Hello Option
6.2.1. Router receives new DRLBGDR 6.2.1. Router Receives New DRLBGDR
When a router receives new DRLBGDR from the current PIM DR, it need When a router receives a new DRLBGDR from the current PIM DR, it need
to process and check if router is in list of of GDR to process and check if router is in list of of GDR
1. If router is not listed as a GDR candidate in DRLBGDR , no action 1. If a router is not listed as a GDR candidate in DRLBGDR, no
needed. action is needed.
2. If 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 need
to process each of the groups in the IGMP/MLD reports. The masks to process each of the groups in the IGMP/MLD reports. The masks
are announced in the PIM Hello by DR as DRLBGDR Hello option. are announced in the PIM Hello by DR as DRLBGDR Hello option.
For each of groups in the reports it need to run hash algorithem For each of groups in the reports it (PIM Router) needs to run
(described in section 4.3) based on the announced Source, Group hash algorithm (described in section 4.3) based on the announced
or RP masks to determine if it is GDR for specified group. If Source, Group or RP masks to determine if it is GDR for specified
hash result is to be GDR for multicast flow, it does build group. If the hash result is to be the GDR for the multicast
multicast forwarding tree. if it is not GDR for flow, no action flow, it does build the multicast forwarding tree. If it is not
is needed. 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 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 needed. current PIM DR, no action is needed.
If 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 need to 1. If it was GDR and still included in current GDR list: it needs to
process each of the groups, run hash algorithem to check if it is process each of the groups and run the hash algorithm to check if
still GDR for given group. it is still the GDR for the given group.
If it was GDR for group earlier. and even new hash choose it If it was the GDR for group G and the new hash result chose it
as GDR, no processing required. as the GDR, then no processing is required.
If it was GDR for group earlier and now it is no more GDR, If it was the GDR for a group earlier and now it is no longer
then it sets its assert metric for this flow to be the GDR, then it sets its assert metric for the multicast flow
(PIM_ASSERT_INFINITY - 1), as explained in Sec 6.3 to be (PIM_ASSERT_INFINITY - 1), as explained in Sec 6.3
If it was not GDR for group earlier, and even new hash does If it was not the GDR for a group earlier, than even the new
not make it GDR no processing required. hash does not make it GDR. For the multicast group no
processing is required.
If it was not GDR earlier and now becomes GDR, it starts If it was not the GDR for an earlier group and now becomes the
building multicast forwarding tree for this flow. GDR, it starts building multicast forwarding tree for this
flow.
2. If it was non GDR , and updated DRLBGDR from current PIM DR 2. If it was not the GDR , and updated DRLBGDR from current PIM DR
contains this router as one of the GDR. In this case this router contains this router as one of the GDR. In this case this router
being new GDR candiate MUST run hash algorithem for each of the being new GDR candidate MUST run hash algorithm for each of the
groups (multicast flows) and for given group, groups (multicast flows) and for given group,
If it is not GDR, no processing is required. If it is not the GDR, no processing is required.
If it is hased as GDR , it need to build multicast forwarding
tree.
3. If a router receives IGMP/MLD report for flow for which the If it is hashed as the GDR , it needs to build multicast
router has been the GDR AND the DRLBGDR has changed since last forwarding tree.
report for this flow, then the router MUST determine if it is
still the GDR. if it is, no action needed. if it is not, then the
router sets its assert metric for this flow to be
(PIM_ASSERT_INFINITY - 1) as explained in Sec 6.3.
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 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 loss might be observed. To illustrate the case, Duplicates or packet losses might be observed. To illustrate the
consider the following scenario: there are two streams G1 and G2. R1 case, consider the following scenario where there are two streams G1
is the GDR for G1, and R2 is the GDR for G2. When R3 comes up and G2. R1 is the GDR for G1, and R2 is the GDR for G2. When R3
online, it is possible that R3 becomes GDR for both G1 and G2, hence comes up online, it is possible that R3 becomes GDR for both G1 and
R3 starts to build the forwarding tree for G1 and G2. If R1 and R2 G2, hence R3 starts to build the forwarding tree for G1 and G2. If
stop forwarding before R3 completes the process, packet loss might R1 and R2 stop forwarding before R3 completes the process, packet
occur. On the other hand, if R1 and R2 continue forwarding while R3 loss might occur. On the other hand, if R1 and R2 continue
is building the forwarding trees, duplicates might occur. forwarding while R3 is building the forwarding trees, duplicates
might occur.
This is not a typical deployment scenario but it still might happen. This is not a typical deployment scenario but might still happen.
Here we describe a mechanism to minimize the impact. The motivation Here we describe a mechanism to minimize the impact. We essentially
is that we want to minimize packet loss. And therefore, we would want to minimize packet loss. Therefore, we would allow a small
allow a small amount of duplicates and depend on PIM Assert to amount of duplicates and depend on PIM Assert to minimize the
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
G1 and G2. This will lead to PIM Asserts. G1 and G2. This will lead to PIM Asserts.
With introduction of GDR, the following modification to the Assert With the introduction of GDR, the following modification to the
packet MUST be done: if a router enables this specification on its Assert packet MUST be done: if a router enables this specification on
downstream interface, but it is not a GDR (before network event it its downstream interface, but it is not a GDR (before network event
was GDR), it would adjust its Assert metric to (PIM_ASSERT_INFINITY - it was GDR), it would adjust its Assert metric to
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 little bit 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 thinks itself being the GDR while R3 that R3 is the new GDR and still considers itself being the GDR while
already has assumed the role of GDR. Since both R2 and R3 think they R3 already has assumed the role of GDR. Since both R2 and R3 think
are GDRs, they further compare the metric and IP address. If R3 has they are GDRs, they further compare the metric and IP address. If R3
the better routing metric, or same metric but better tie-breaker, the has the better routing metric, or the same metric but a better tie-
result will be consistent with GDR selection. If unfortunately, R2 breaker, the result will be consistent during GDR selection. If
has the better metric or same metric but better tie-breaker R2 will unfortunately, R2 has the better metric or the same metric but a
become the Assert winner and continues to forward traffic. This will better tie-breaker, R2 will become the Assert winner and continues to
continue until: forward traffic. This will continue until:
The next PIM Hello option from DR is seen that selects R3 as the GDR. The next PIM Hello option from DR selects R3 as the GDR. R3 will
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 being The process continues until R2 agrees to the selection of R3 as the
the GDR, and set its own Assert metric to (PIM_ASSERT_INFINITY - 1), GDR, and set 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 hybrid Ethernet shared LAN ( where some PIM router enables In case of the hybrid Ethernet shared LAN ( where some PIM router
specification defined in this draft and some do not enable) enables specification defined in this draft and some do not enable)
o If router which does not support specification defined in this o If a router which does not support specification defined in this
draft becomes DR on link, it MUST be only DR on link as [RFC4601] draft becomes DR on link, it MUST be only DR on link as [RFC4601]
and there would be no router which would act as GDR. and there would be no router which would act as GDR.
o If router which does not support specification defined in this o If a router which does not support specification defined in this
draft becomes non DR on link, then it should act as non-DR defined draft becomes non DR on link, then it should act as non-DR defined
in [RFC4601]. in [RFC4601].
8. Manageability Considerations 8. Manageability Considerations
o All of the router in LAN who are supporting this specification o All of the routers in LAN that support this specification MUST use
MUST use identical Hash Algorithm Type (described in section 5.1). identical Hash Algorithm Type (described in section 5.1). In the
In case of hybrid Hash Algorithm Type router must go backward to case of a hybrid Hash Algorithm Type, one MUST go backward to use
use DR election method defined in PIM-SM [RFC4601]. Migration DR election method defined in PIM-SM [RFC4601]. Migration between
between different algorithem type is out of scope of this different algorithm type is out of the scope of this document.
document.
9. IANA Considerations 9. IANA Considerations
Two new PIM Hello Option Types have been assigned to the DR Load IANA has temporarily assigned type 34 for the PIM DR Load Balancing
Balancing messages. [HELLO-OPT], this document recommends 34(0x22) Capability (DRLBC) Hello Option, and type 35 for the PIM DR Load
as the new "PIM DR Load Balancing Capability Hello Option", and Balancing GDR (DRLBGDR) Hello Option. IANA is requested to make
35(0x23) as the new "PIM DR Load Balancing GDR Hello Option". these assignments permanent when this document is published as an
RFC. The string TBD should be replaced by the assigned values
accordingly.
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 message, 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. [RFC4601] 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
Holland for reviewing the document and providing comments.
12. References 12. References
12.1. Normative References 12.1. Normative References
[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
skipping to change at page 17, line 29 skipping to change at page 17, line 29
Alibaba Group Alibaba Group
Sri Vallepalli Sri Vallepalli
Cisco Systems Cisco Systems
3625 Cisco Way, 3625 Cisco Way,
Sanjose, CALIFORNIA 95134 Sanjose, CALIFORNIA 95134
UNITED STATES UNITED STATES
Email: svallepa@cisco.com Email: svallepa@cisco.com
Mankamana Prasad Mishra Mankamana Mishra
Cisco Systems Cisco Systems
821 Alder Drive, 821 Alder Drive,
MILPITAS, CALIFORNIA 95035 MILPITAS, CALIFORNIA 95035
UNITED STATES UNITED STATES
Email: mankamis@cisco.com Email: mankamis@cisco.com
Stig Venaas Stig Venaas
Cisco Systems Cisco Systems
821 Alder Drive, 821 Alder Drive,
 End of changes. 90 change blocks. 
218 lines changed or deleted 215 lines changed or added

This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/