draft-ietf-pim-drlb-03.txt   draft-ietf-pim-drlb-04.txt 
Network Working Group Yiqun Cai Network Working Group Yiqun Cai
Internet-Draft Microsoft Internet-Draft Microsoft
Intended status: Standards Track Sri Vallepalli Intended status: Standards Track Sri Vallepalli
Expires: August 19, 2014 Heidi Ou Expires: December 13, 2014 Heidi Ou
Cisco Systems, Inc. Cisco Systems, Inc.
Andy Green Andy Green
British Telecom British Telecom
February 15, 2014 June 11, 2014
PIM Designated Router Load Balancing PIM Designated Router Load Balancing
draft-ietf-pim-drlb-03.txt draft-ietf-pim-drlb-04.txt
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 network, the PIM DR is Designated Router (DR). On the last hop network, 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 operated 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 to and handled among these the forwarding load can be distributed among these routers.
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.
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This Internet-Draft will expire on August 19, 2014. This Internet-Draft will expire on December 13, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 6 4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 5
4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . . 7 4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . 6
4.2. Hash Mask . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Hash Mask and Hash Algorithm . . . . . . . . . . . . . . 7
4.3. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 8 4.3. Modulo Hash Algorithm . . . . . . . . . . . . . . . . . . 8
5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . . 9 4.4. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 9
5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 9 5. Hello Option Formats . . . . . . . . . . . . . . . . . . . . 9
5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option . . . . . 10 5.1. PIM DR Load Balancing Capability (DRLBC) Hello Option . . 9
6. Protocol Specification . . . . . . . . . . . . . . . . . . . . 11 5.2. PIM DR Load Balancing GDR (DRLBGDR) Hello Option . . . . 10
6.1. PIM DR Operation . . . . . . . . . . . . . . . . . . . . . 11 6. Protocol Specification . . . . . . . . . . . . . . . . . . . 11
6.2. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 11 6.1. PIM DR Operation . . . . . . . . . . . . . . . . . . . . 11
6.3. PIM Assert Modification . . . . . . . . . . . . . . . . . 12 6.2. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6.3. PIM Assert Modification . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative Reference . . . . . . . . . . . . . . . . . . . 14 10. Normative Reference . . . . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Terminology 1. 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
group, a hash algorithm (described below) is used to select one of flow, either a (*,G) for ASM, or an (S,G) for SSM, a hash
the routers as a GDR. The GDR is responsible for initiating the algorithm (described below) is used to select one of the routers
forwarding tree building for the corresponding group. as a GDR. The GDR is responsible for initiating the forwarding
tree building 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 potential to become a
GDR. A GDR Candidate must have the same DR priority and must run GDR. A GDR Candidate must have the same DR priority and must run
the same GDR election hash algorithm as the DR router. It must the same GDR election hash algorithm as the DR router. It must
send and process received new PIM Hello Options as defined in this 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 group. But only one can become GDR for a specific multicast flow.
2. Introduction 2. Introduction
On a multi-access network such as an Ethernet, one of the PIM routers On a multi-access network such as an Ethernet, one of the PIM routers
is elected as a DR. The PIM DR has two roles in the PIM protocol. is 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 network, the PIM DR is responsible for registering
an active source with the Rendezvous Point (RP) if the group is an active source with the Rendezvous Point (RP) if the group is
operated in PIM SM. On the last hop network, the PIM DR is operating in PIM-SM. On the last hop network, the PIM DR is
responsible for tracking local multicast listeners and forwarding to responsible for tracking local multicast listeners and forwarding to
these listeners if the group is operated in PIM SM. these listeners if the group is operating in PIM-SM.
Consider the following last hop network in Figure 1: Consider the following last hop network 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 Network Figure 1: Last Hop Network
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 to the last hop LAN. [RFC4601], R1 will be responsible for forwarding traffic to that LAN
In addition to keeping track of IGMP and MLD membership reports, R1 on behalf of any local members. In addition to keeping track of IGMP
is also responsible for initiating the creation of source and/or and MLD membership reports, R1 is also responsible for initiating the
shared trees towards the senders or the RPs. creation of source and/or shared trees towards the senders or the
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 proves 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). The forwarding load of a last hop LAN
is concentrated on a single router. is concentrated on a single router.
skipping to change at page 5, line 24 skipping to change at page 4, line 38
+=gi4===gi5===gi6=+ +=gi4===gi5===gi6=+
| | | | | |
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 data and different traffic is requested by each host. This
represents a total 1.5 gbps of data, which is under what each switch represents a total 1.5 Gbps of data, which is under what each switch
or the combined uplink bandwidth across the routers can handle, even or the combined uplink bandwidth across 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 router, the
PIM DR elected using the procedure defined by RFC 4601, at least 500 PIM 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 requests 300 Mbps of different
multicast data. Once again packet drop happens on R1 while in the multicast data. Once again packet drop happens on R1 while in the
mean time, there is sufficient forwarding capacity left on R2 and R3 mean time, there is sufficient forwarding capacity left on R2 and R3
and link capacity between the switch and R2/R3. and 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 network, in the event of a failure when R1 forwarder on the last hop network, in the event of a failure when R1
goes out of service, multicast forwarding for the entire network has goes out of service, multicast forwarding for the entire network has
to be rebuilt by the newly elected PIM DR. However, if there was a to be rebuilt by the newly elected PIM DR. However, if there was a
way that allowed multiple routers to forward to the network for way that allowed multiple routers to forward to the network for
different groups, failure of one of the routers would only lead to different groups, failure of one of the routers would only lead to
disruption to a subset of the flows, therefore improving the overall disruption to a subset of the flows, therefore improving the overall
resilience of the network. resilience of the network.
In this document, we propose a modification to the PIM protocol that In this document, we propose a modification to the PIM-SM protocol
allows more than one of these routers, called Group Designated Router that allows more than one of these routers, called Group Designated
(GDR) to be selected so that the forwarding load can be distributed Router (GDR) to be selected so that the forwarding load can be
to and handled by a number of routers. distributed among a number of routers.
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). And distributing the load to do
registering does not justify the additional complexity required to 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 network (for example, an Ethernet), one connected to a multi-access network (for example, an Ethernet), one
of them is selected to act as PIM DR. The PIM DR is responsible for of them is selected to act as PIM DR. The PIM DR is responsible for
sending Join/Prune messages towards the RP or source. To elect the sending local Join/Prune messages towards the RP or source. To elect
PIM DR, each PIM router on the network examines the received PIM the PIM DR, each PIM router on the network examines the received PIM
Hello messages and compares its DR priority and IP address with those Hello messages and compares its DR priority and IP address with those
of its neighbors. The router with the highest DR priority is the PIM of its neighbors. The router with the highest DR priority is the PIM
DR. If there are multiple such routers, their IP addresses are used DR. If there are multiple such routers, their IP addresses are used
as the tie-breaker, as described in [RFC4601]. 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 network. There is only one PIM DR on the multi-access multi-access network. There is only one PIM DR on the multi-access
network, but there might be multiple GDR Candidates. network, but there might be multiple GDR Candidates.
For each multicast group, a hash algorithm is used to select one of 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
new DR Load Balancing Capability (DRLBC) PIM Hello Option, which
contains hash algorithm type, is announced by routers 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.
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
Candidates' Addresses are announced by DR in a new DR Load Balancing
GDR (DRLBGDR) PIM Hello Option.
For each multicast flow, a hash algorithm is used to select one of
the routers to be the GDR. Hash Masks are defined for Source, Group the routers to be the GDR. Hash Masks are defined for Source, Group
and RP separately, in order to handle PIM ASM/SSM. The masks are and RP separately, in order to handle PIM ASM/SSM. The masks are
announced in PIM Hello by DR as a DR Load Balancing GDR (DRLBGDR) 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. Besides that, a DR Load Balancing Capability (DRLBC)
Hello Option, which contains hash algorithm type, is also announced Hello Option, which contains hash algorithm type, is also announced
by router interfaces which have this specification supported. Last by the router on interfaces where this specification is enabled.
hop routers who are with the new DRLBC Option, and with the same GDR Last hop routers with the new DRLBC Option advertised in its Hello,
election hash algorithm and the same DR priority as the PIM DR are and using the same GDR election hash algorithm and the same DR
GDR Candidates. priority as the PIM DR, are considered as GDR Candidates.
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 group, and allows one GDR to be assigned to a corresponding multicast state.
that GDR is responsible for initiating the creation of the multicast And that GDR is responsible for initiating the creation of the
forwarding tree for the group. 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
skipping to change at page 7, line 36 skipping to change at page 7, line 17
service. service.
Further assume router R1 wins the PIM DR election, and R1, R2 run the Further assume router R1 wins the PIM DR election, and R1, R2 run the
same hash algorithm for GDR election, while R3 runs a different one. same hash algorithm for GDR election, while R3 runs a different one.
Then only R1 and R2 will be eligible for GDR election, R3 will not. Then only R1 and R2 will be eligible for GDR election, 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 also
the identity of R1 and R2 (the GDR Candidates) in its DRLBGDR Hello the identity of R1 and R2 (the GDR Candidates) in its DRLBGDR Hello
Option. Option.
4.2. Hash Mask 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, 0.255.0.0 defines a Candidates advertised by PIM DR. For example, 0.255.0.0 defines a
Hash Mask for an IPv4 address that masks the first, the third and the Hash Mask for an IPv4 address that masks the first, the third and the
fourth octets. fourth octets.
There are three Hash Masks defined, There are three Hash Masks defined,
skipping to change at page 7, line 48 skipping to change at page 7, line 29
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, 0.255.0.0 defines a Candidates advertised by PIM DR. For example, 0.255.0.0 defines a
Hash Mask for an IPv4 address that masks the first, the third and the Hash Mask for an IPv4 address that masks the first, the third and the
fourth octets. 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 MUST be configured on the PIM routers that can The Hash Masks MUST be configured on the PIM routers that can
potentially become a PIM DR. potentially become a PIM DR.
o If the group is ASM, and if the RP Hash Mask announced by the PIM
DR is not 0, calculate the value of hashvalue_RP to determine GDR.
o If the group is ASM and if the RP Hash Mask announced by the PIM
DR is 0, obtain the value of hashvalue_Group to to determine GDR.
o If the group is SSM, use hashvalue_SG to determine 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 other hash algorithm 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.
For ASM groups, a hash value is calculated using the following Modulo 4.3. Modulo Hash Algorithm
algorithm:
o hashvalue_RP = (((RP_address & RP_hashmask) >> N) & 0xFFFF) % M Modulo hash algorithm is discussed here as an example, with detailed
description on hashvalue_RP.
RP_address is the address of the RP defined for the group. N is the For ASM groups, with a non-zero RP_hash mask, hash value is
number of zeros, counted from the least significant bit of the calculated as:
RP_hashmask. For example, for a given IPv4 RP_hashmask 0.255.0.0, N
will be 16. M is the number of GDR Candidates as described above.
If RP_hashmask is 0, a hash value is also calculated using the group * hashvalue_RP = (((RP_address & RP_hashmask) >> N) & 0xFFFF) % M
Hash Mask in a similar fashion.
o hashvalue_Group = (((Group_address & Group_hashmask) >> N) & RP_address is the address of the RP defined for the group. N is
0xFFFF) % M the number of zeros, counted from the least significant bit of the
RP_hashmask. M is the number of GDR Candidates.
For example, Router X with IPv4 address 203.0.113.1, receives a
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
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:
0 for 203.0.113.3; 1 for 203.0.113.2; 2 for 203.0.113.1 (Router X)
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:
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:
(((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 be
the GDR for Group1, which uses 192.0.2.1 as the RP.
The hashvalue_RP for RP2 198.51.100.2 is:
(((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, Router
X will not be GDR for Group2.
If RP_hashmask is 0, a hash value for ASM group is calculated using
the group Hash Mask:
* hashvalue_Group = (((Group_address & Group_hashmask) >> N) &
0xFFFF) % M
Compare hashvalue_Group with Ordinal number assigned to Router X,
to decide if Router X is the GDR.
For SSM groups, a hash value is calculated using both the source and For SSM groups, a hash value is calculated using both the source and
group Hash Mask group Hash Mask
o 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. 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 specificiation support, 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 addresses of all GDR Candidates on the last hop network. the sorted list of all GDR Candidates' Address on the last hop
network.
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 network to compose its DRLBGDR . The GDR Candidates on the last hop network to compose its DRLBGDR . The GDR Candidates
use DRLBGDR Hello Option advertised by PIM DR to calculate hash use DRLBGDR Hello Option advertised by PIM DR to calculate hash
value. 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 9, line 22 skipping to change at page 10, line 15
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
Type: TBD. Type: TBD.
Length: 4 octets Length: 4 octets
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 SHOULD be advertised by last hop routers from
interfaces which support this specification. 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 24 skipping to change at page 10, line 42
| Source Mask | | Source Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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: Length:
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, with the same
length. All masks MUST be in the same address family as the Hello IP
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. The addresses
are sorted from high to low. The order is converted to the All addresses must be in the same address family as the Hello IP
ordinal number associated with each GDR candidate in hash value header. The addresses are sorted from high to low. The order is
calculation. For example, addresses advertised are R3, R2, R1, converted to the ordinal number associated with each GDR candidate
the ordinal number assigned to R3 is 0, to R2 is 1 and to R1 is 2. in hash value calculation. For example, addresses advertised are
If "Interface ID" option (type 31) presents in a GDR Candicate's R3, R2, R1, the ordinal number assigned to R3 is 0, to R2 is 1 and
PIM Hello message, and the "Router ID" portion is non-zero, to R1 is 2.
If "Interface ID" option, as described in [RFC6395], presents in a
GDR Candicate's PIM Hello message, and the "Router ID" portion is
non-zero,
* For IPv4, the "GDR Candidate Address" will be set directly to * For IPv4, the "GDR Candidate Address" will be set directly to
"Router ID". "Router ID".
* For IPv6, the "GDR Candidate Address" will be set to the IPv4-
IPv6 translated address of "Router ID", as described in * For IPv6, the "GDR Candidate Address" will be set to the
IPv4-IPv6 translated address of "Router ID", as described in
[RFC4291], that is the "Router-ID" is appended to the prefix of [RFC4291], that is the "Router-ID" is appended to the prefix of
96-bits zeros. 96-bits zeros.
If the "Interface ID" option is not present in a GDR Candidate's If the "Interface ID" option is not present in a GDR Candidate's
PIM Hello message, or if the "Interface ID" option is present, PIM Hello message, or if the "Interface ID" option is present,
but"Router ID" field is zero, the "GDR Candidate Address" will be but"Router ID" field is zero, the "GDR Candidate Address" will be
the IPv4 or IPv6 source address from PIM Hello message. the IPv4 or IPv6 source address from PIM Hello message.
This DRLBGDR Hello Option SHOULD only be advertised by the elected This DRLBGDR Hello Option SHOULD only be advertised by the elected
PIM DR. 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 LBGRD Hello Option, which contains value of masks from user
configuration, followed by a sorted list of addresses of all GDR configuration, followed by a sorted list of all GDR Candidates'
Candidates. Moreover, same as non-DR routers, DR also advertises Addresses, from high to low. Moreover, same as non-DR routers, DR
DRLBC Hello Option to indicate its capability of supporting this also advertises DRLBC Hello Option to indicate its capability of
specification and the type of its GDR election hash algorithm. supporting this specification and the type of its GDR election hash
algorithm.
If a PIM DR receives a neighbor Hello with DRLBGRD Option, the PIM DR If a PIM DR receives a PIM Hello with DRLBGRD 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 neighbor's address into the sorted list of Candidate and insert the GDR Candidate's Address into the sorted list
DRLBGRD Option. of DRLBGRD Option.
6.2. PIM GDR Candidate Operation 6.2. PIM GDR Candidate Operation
When an IGMP join is received, without this proposal, router R1 (the When an IGMP/MLD join is received, without this proposal, only PIM DR
PIM DR) will handle the join and potentially run into the issues will handle the join and potentially run into the issues described
described earlier. Using this proposal, a hash algorithm is used to earlier. Using this proposal, a hash algorithm is used on GDR
determine which router is going to be responsible for building Candidate to determine which router is going to be responsible for
forwarding trees on behalf of the host. building forwarding trees on behalf of the host.
The algorithm works as follows, assuming the router in question is X,
which is a GDR Candidate, and its ordinal number assigned implicitly
by PIM DR in DRLBGDR Hello Option is Ox:
o If the group is ASM, and the RP Hash Mask announced by the PIM DR
is not zero, calculate the value of hashvalue_RP. If hashvalue_RP
is equal to Ox, X becomes the GDR.
For example, X with IPv4 address 10.1.1.3, receives a DRLBGDR Hello
Option from the DR, which announces RP Hash Mask 0.255.0.0, and a
list of GDR Candidates, sorted by IP addresses from high to low,
10.1.1.3, 10.1.1.2 and 10.1.1.1. The ordinal number assigned to
those addresses would be 0 for 10.1.1.3 (X), 1 for 10.1.1.2, and 2
for 10.1.1.1. Assume there are 2 RPs: RP1 172.3.10.10 for Group1 and
RP2 172.2.10.10 for Group2. Following the modulo hash algorithm
hashvalue_RP = (((RP_address & RP_hashmask) >> N) & 0xFFFF) % M
Here N is 16 for 0.255.0.0, and M is 3 for the total number of GDR
Candidates. The hasvalue_RP for RP1 172.3.10.10 is 0, matches the
ordinal number assigned to X. X will be the GDR for Group1, which
uses 172.3.10.10 as the RP. The hashvalue_RP for RP2 172.2.10.10 is
2, which is different from X's ordinal number, hence, X will not be
GDR for Group2.
o If the group is ASM, and the RP Hash Mask announced by the PIM DR
is zero, obtain the value of hashvalue_Group. Compare
hashvalue_Group with Ox, to decide if X is the GDR.
o If the group is SSM, then use hashvalue_SG to determine if X is
the GDR.
If X is the GDR for the group, X will be responsible for building the
forwarding tree.
A router interface where this protocol is enabled advertises DRLBC A router interface where this protocol is enabled advertises DRLBC
Hello Option in its PIM Hello, even if the router may not be a GDR Hello Option in its PIM Hello, even if the router may not be
Candidate. considered as a GDR Candidate, for example, due to low DR priority.
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 non-DR PIM A GDR Candidate may receive a DRLBGDR Hello Option from a PIM router
router. The GDR Candidate must ignore such DRLBGDR Hello Option. which is not DR. The GDR Candidate must ignore such DRLBGDR Hello
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.
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:
1. When a new PIM router comes up
2. When a GDR restarts o When a new PIM router comes up
o 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 loss might be observed. To illustrate the case,
consider the following scenario: there are two streams G1 and G2. R1 consider the following scenario: there are two streams G1 and G2. R1
is the GDR for G1, and R2 is the GDR for G2. When R3 comes up is the GDR for G1, and R2 is the GDR for G2. When R3 comes up
online, it is possible that R3 becomes GDR for both G1 and G2, hence online, it is possible that R3 becomes GDR for both G1 and G2, hence
R2 starts to build the forwarding tree for G1 and G2. If R1 and R2 R3 starts to build the forwarding tree for G1 and G2. If R1 and R2
stop forwarding before R3 completes the process, packet loss might stop forwarding before R3 completes the process, packet loss might
occur. On the other hand, if R1 and R2 continue forwarding while R3 occur. On the other hand, if R1 and R2 continue forwarding while R3
is building the forwarding trees, duplicates might occur. 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 it still might happen.
Here we describe a mechanism to minimize the impact. The motivation Here we describe a mechanism to minimize the impact. The motivation
is that we want to minimize packet loss. And therefore, we would is that we want to minimize packet loss. And therefore, we would
allow a small amount of duplicates and depend on PIM Assert to allow a small amount of duplicates and depend on PIM Assert to
minimize the duplication. minimize the 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.
Due to the introduction of GDR, this document suggests the following Due to the introduction of GDR, this document suggests the following
modification to the Assert packet: if a router enables this modification to the Assert packet: if a router enables this
specification on its downstream interface, but it is not a GDR, it specification on its downstream interface, but it is not a GDR, it
would adjust its Assert metric to (PIM_ASSERT_INFINITY - 1). would adjust its Assert metric to (PIM_ASSERT_INFINITY - 1).
Using the above example, assume R1 and R3 agree on the new GDR, which Using the above example, for G1, assume R1 and R3 agree on the new
is R3. R1 will set its Assert metric as (PIM_ASSERT_INFINITY - 1). GDR, which is R3. R1 will set its Assert metric as
That will make R3, which has normal metric in its Assert as the (PIM_ASSERT_INFINITY - 1). That will make R3, which has normal
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 little bit 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 thinks itself being the GDR while R3
already has assumed the role of GDR. Since both R2 and R3 think they 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 has are GDRs, they further compare the metric and IP address. If R3 has
the better routing metric, or same metric but better tie-breaker, the the better routing metric, or same metric but better tie-breaker, the
result will be consistent with GDR selection. If unfortunately, R2 result will be consistent with GDR selection. If unfortunately, R2
has the better metric or same metric but better tie-breaker R2 will has the better metric or same metric but better tie-breaker R2 will
become the Assert winner and continues to forward traffic. This will become the Assert winner and continues to forward traffic. This will
continue until: continue until:
1. The next PIM Hello option from DR is seen that selects R3 as the
GDR. The next PIM Hello option from DR is seen that selects R3 as the
2. R3 will build the forwarding tree and send an Assert. GDR. R3 will 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 being
the GDR, and set its own Assert metric to (PIM_ASSERT_INFINITY - 1), the 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. IANA Considerations 7. IANA Considerations
Two new PIM Hello Option Types are required to be assigned to the DR Two new PIM Hello Option Types have been assigned to the DR Load
Load Balancing messages. [HELLO-OPT], this document recommends Balancing messages. [HELLO-OPT], this document recommends 34(0x22)
34(0x22) as the new "PIM DR Load Balancing Capability Hello Option", as the new "PIM DR Load Balancing Capability Hello Option", and
and 35(0x23) as the new "PIM DR Load Balancing GDR Hello Option". 35(0x23) as the new "PIM DR Load Balancing GDR Hello Option".
8. Security Considerations 8. Security Considerations
Security of the PIM DR Load Balancing Hello message 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.
9. Acknowledgement 9. 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 for review comments, Stig helping with the original idea, Bill Atwood, Bharat Joshi for review
Venaas, Toerless Eckert and Rishabh Parekh for helpful conversation comments, Stig Venaas, Toerless Eckert and Rishabh Parekh for helpful
on the document. conversation on the document.
10. References
10.1. Normative Reference 10. Normative Reference
[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, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM): "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006. Protocol Specification (Revised)", RFC 4601, August 2006.
10.2. Informative References
[RFC3973] Adams, A., Nicholas, J., and W. Siadak, "Protocol
Independent Multicast - Dense Mode (PIM-DM): Protocol
Specification (Revised)", RFC 3973, January 2005.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
[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, October 2011. Hello Option for PIM", RFC 6395, October 2011.
[RFC4291] Hinden, R. and L. S., "IP Version 6 Addressing [RFC4291] Hinden, R. and L. S., "IP Version 6 Addressing
Architecture", RFC 6890, February 2006. Architecture", RFC 6890, February 2006.
[HELLO-OPT] [HELLO-OPT]
IANA, "PIM Hello Options", PIM-HELLO-OPTIONS per IANA, , "PIM Hello Options", PIM-HELLO-OPTIONS per RFC4601
RFC4601 http://www.iana.org/assignments/pim-hello-options, http://www.iana.org/assignments/pim-hello-options, March
March 2007. 2007.
Authors' Addresses Authors' Addresses
Yiqun Cai Yiqun Cai
Microsoft Microsoft
La Avenida La Avenida
Mountain View, CA 94043 Mountain View, CA 94043
USA USA
Email: yiqunc@microsoft.com Email: yiqunc@microsoft.com
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