draft-ietf-pim-drlb-11.txt   draft-ietf-pim-drlb-12.txt 
Network Working Group Y. Cai Network Working Group Y. Cai
Internet-Draft H. Ou Internet-Draft H. Ou
Intended status: Standards Track Alibaba Group Intended status: Standards Track Alibaba Group
Expires: April 13, 2020 S. Vallepalli Expires: April 25, 2020 S. Vallepalli
M. Mishra M. Mishra
S. Venaas S. Venaas
Cisco Systems, Inc. Cisco Systems, Inc.
A. Green A. Green
British Telecom British Telecom
October 11, 2019 October 23, 2019
PIM Designated Router Load Balancing PIM Designated Router Load Balancing
draft-ietf-pim-drlb-11 draft-ietf-pim-drlb-12
Abstract Abstract
On a multi-access network, one of the PIM-SM routers is elected as a On a multi-access network, one of the PIM-SM routers is elected as a
Designated Router. One of the responsibilities of the Designated Designated Router. One of the responsibilities of the Designated
Router is to track local multicast listeners and forward data to Router is to track local multicast listeners and forward data to
these listeners if the group is operating in PIM-SM. This document these listeners if the group is operating in PIM-SM. This document
specifies a modification to the PIM-SM protocol that allows more than specifies a modification to the PIM-SM protocol that allows more than
one of the PIM-SM routers to take on this responsibility so that the one of the PIM-SM routers to take on this responsibility so that the
forwarding load can be distributed among multiple routers. forwarding load can be distributed among multiple routers.
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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-
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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 April 13, 2020. This Internet-Draft will expire on April 25, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
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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 . . . . . . . . . . . . . . . . . . . . . 5 4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 5
4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . 6 4.1. GDR Candidates . . . . . . . . . . . . . . . . . . . . . 6
5. Protocol Specification . . . . . . . . . . . . . . . . . . . 7 5. Protocol Specification . . . . . . . . . . . . . . . . . . . 7
5.1. Hash Mask and Hash Algorithm . . . . . . . . . . . . . . 7 5.1. Hash Mask and Hash Algorithm . . . . . . . . . . . . . . 7
5.2. Modulo Hash Algorithm . . . . . . . . . . . . . . . . . . 8 5.2. Modulo Hash Algorithm . . . . . . . . . . . . . . . . . . 8
5.2.1. Modulo Hash Algorithm Example . . . . . . . . . . . . 9 5.2.1. Modulo Hash Algorithm Examples . . . . . . . . . . . 9
5.2.2. Limitations . . . . . . . . . . . . . . . . . . . . . 10 5.2.2. Limitations . . . . . . . . . . . . . . . . . . . . . 10
5.3. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 10 5.3. PIM Hello Options . . . . . . . . . . . . . . . . . . . . 10
5.3.1. PIM DR Load Balancing Capability (DRLB-Cap) Hello 5.3.1. PIM DR Load Balancing Capability (DRLB-Cap) Hello
Option . . . . . . . . . . . . . . . . . . . . . . . 10 Option . . . . . . . . . . . . . . . . . . . . . . . 11
5.3.2. PIM DR Load Balancing List (DRLB-List) Hello Option . 11 5.3.2. PIM DR Load Balancing List (DRLB-List) Hello Option . 11
5.4. PIM DR Operation . . . . . . . . . . . . . . . . . . . . 12 5.4. PIM DR Operation . . . . . . . . . . . . . . . . . . . . 13
5.5. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 13 5.5. PIM GDR Candidate Operation . . . . . . . . . . . . . . . 13
5.6. DRLB-List Hello Option Processing . . . . . . . . . . . . 13 5.6. DRLB-List Hello Option Processing . . . . . . . . . . . . 14
5.7. PIM Assert Modification . . . . . . . . . . . . . . . . . 14 5.7. PIM Assert Modification . . . . . . . . . . . . . . . . . 15
5.8. Backward Compatibility . . . . . . . . . . . . . . . . . 16 5.8. Backward Compatibility . . . . . . . . . . . . . . . . . 16
6. Manageability Considerations . . . . . . . . . . . . . . . . 16 6. Operational Considerations . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. Initial registry . . . . . . . . . . . . . . . . . . . . 17 7.1. Initial registry . . . . . . . . . . . . . . . . . . . . 17
7.2. Assignment of new hash algorithms . . . . . . . . . . . . 17 7.2. Assignment of new Hash Algorithms . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 18 10.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
On a multi-access LAN, such as an Ethernet, with one or more PIM-SM On a multi-access LAN, such as an Ethernet, with one or more PIM-SM
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14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
With respect to PIM-SM, this document follows the terminology that With respect to PIM-SM, this document follows the terminology that
has been defined in [RFC7761]. has been defined in [RFC7761].
This document also introduces the following new acronyms: This document also introduces the following new acronyms:
o GDR: Group Designated Router. For each multicast flow, either a o GDR: Group Designated Router. For each multicast flow, either a
(*,G) for Any-Source Multicast (ASM), or an (S,G) for Source- (*,G) for Any-Source Multicast (ASM), or an (S,G) for Source-
Specific Multicast (SSM) [RFC4607], a hash algorithm (described Specific Multicast (SSM) [RFC4607], a Hash Algorithm (described
below) is used to select one of the routers as a GDR. The GDR is below) is used to select one of the routers as a GDR. The GDR is
responsible for initiating the forwarding tree building process responsible for initiating the forwarding tree building process
for the corresponding multicast flow. for the corresponding multicast flow.
o GDR Candidate: a router that has the potential to become a GDR. o GDR Candidate: a router that has the potential to become a GDR.
There might be multiple GDR Candidates on a LAN, but only one can There might be multiple GDR Candidates on a LAN, but only one can
become the GDR for a specific multicast flow. become the GDR for a specific multicast flow.
3. Applicability 3. Applicability
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with those of its neighbors. The router with the highest DR priority with those of its neighbors. The router with the highest DR priority
is the PIM DR. If there are multiple such routers, their IP is the PIM DR. If there are multiple such routers, their IP
addresses are used as the tie-breaker, as described in [RFC7761]. addresses are used as the tie-breaker, as described in [RFC7761].
In order to share forwarding load among last hop routers, besides the In order to share forwarding load among last hop routers, besides the
normal PIM DR election, the GDR is also elected on the multi-access normal PIM DR election, the GDR is also elected on the multi-access
LAN. There is only one PIM DR on the multi-access LAN, but there LAN. There is only one PIM DR on the multi-access LAN, but there
might be multiple GDR Candidates. 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.
new DR Load Balancing Capability (DRLB-Cap) PIM Hello Option, which The new DR Load Balancing Capability (DRLB-Cap) PIM Hello Option is
contains hash algorithm type, is announced by routers on interfaces used to announce the Capability as well as the Hash Algorithm type.
where this specification is enabled. Routers with the new DRLB-Cap Routers with the new DRLB-Cap Option advertised in their PIM Hello,
Option advertised in their PIM Hello, using the same GDR election using the same GDR election Hash Algorithm and the same DR priority
hash algorithm and the same DR priority as the PIM DR, are considered 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
Candidate Addresses, are announced by the DR in a new DR Load Candidate Addresses, are announced by the DR in a new DR Load
Balancing List (DRLB-List) PIM Hello Option. Balancing List (DRLB-List) PIM Hello Option.
A hash algorithm based on the announced Source, Group, or RP masks A Hash Algorithm based on the announced Source, Group, or RP masks
allows one GDR to be assigned to a corresponding multicast state. allows one GDR to be assigned to a corresponding multicast state.
And that GDR is responsible for initiating the creation of the And that GDR is responsible for initiating the creation of the
multicast forwarding tree for multicast traffic. multicast forwarding tree for multicast traffic.
4.1. GDR Candidates 4.1. GDR Candidates
GDR is the new concept introduced by this specification. GDR GDR is the new concept introduced by this specification. GDR
Candidates are routers eligible for GDR election on the LAN. To Candidates are routers eligible for GDR election on the LAN. To
become a GDR Candidate, a router must have the same DR priority and become a GDR Candidate, a router must have the same DR priority and
run the same GDR election hash algorithm as the DR on the LAN. run the same GDR election Hash 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, each announcing a DRLB-Cap option. R1, R2 and R3 have the same R4, each announcing a DRLB-Cap option. R1, R2 and R3 have the same
DR priority while R4's DR priority is less preferred. In this DR priority while R4's DR priority is less preferred. In this
example, R4 will not be eligible for GDR election, because R4 will example, R4 will not be eligible for GDR election, because R4 will
not become a PIM DR unless all of R1, R2 and R3 go out of service. not become a PIM DR unless all of R1, R2 and R3 go out of service.
Furthermore, assume router R1 wins the PIM DR election, R1 and R2 run Furthermore, assume router R1 wins the PIM DR election, R1 and R2 run
the same hash algorithm for GDR election, while R3 runs a different the same Hash Algorithm for GDR election, while R3 runs a different
one. In this case, only R1 and R2 will be eligible for GDR election, one. In this case, only R1 and R2 will be eligible for GDR election,
while R3 will not. while R3 will not.
As a DR, R1 will include its own Load Balancing Hash Masks and the As a DR, R1 will include its own Load Balancing Hash Masks and the
identity of R1 and R2 (the GDR Candidates) in its DRLB-List Hello identity of R1 and R2 (the GDR Candidates) in its DRLB-List Hello
Option. Option.
5. Protocol Specification 5. Protocol Specification
5.1. Hash Mask and Hash Algorithm 5.1. 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 IPv4, 128 for IPv6) and corresponding IP address field (32 for IPv4, 128 for IPv6) and
calculate a hash value. A hash value is used to select a GDR from calculate 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 GDR Candidates advertised by the PIM DR. Hash masks allow for
a Hash Mask for an IPv4 address that masks the first, the second, and certain flows to always be forwarded by the same GDR, by ignoring
the fourth octets. Hash masks allow for certain flows to always be certain bits in the hash value calculation, so that the hash values
forwarded by the same GDR, since the hash values are the same. For are the same. For example, 0.0.255.0 defines a Hash Mask for an IPv4
instance the mask 0.0.255.0 means that only the third octet will be address that masks the first, the second, and the fourth octets,
considered when hashing. which means that only the third octet will influence the hash value
computed.
In the text below, a hash mask is in some places said to be zero. A In the text below, a hash mask is in some places said to be zero. A
hash mask is zero if no bits are set. That is, 0.0.0.0 for IPv4 and hash mask is zero if no bits are set. That is, 0.0.0.0 for IPv4 and
:: for IPv6. Also, a hash mask is said to be an all-bits-set mask if :: for IPv6. Also, a hash mask is said to be an all-bits-set mask if
it is 255.255.255.255 for IPv4 or it is 255.255.255.255 for IPv4 or
FFFF:FFFF:FFFF:FFFF:FFFFF:FFFF:FFFF:FFFF for IPv6. FFFF:FFFF:FFFF:FFFF:FFFFF:FFFF:FFFF:FFFF for IPv6.
There are three Hash Masks defined: There are three Hash Masks defined:
o RP Hash Mask o RP Hash Mask
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PIM DR is not zero (at least one bit is set), calculate the value PIM DR is not zero (at least one bit is set), calculate the value
of hashvalue_RP [Section 5.2] to determine the GDR. of hashvalue_RP [Section 5.2] to determine the GDR.
o If the group is in ASM mode and the RP Hash Mask announced by the o If the group is in ASM mode and the RP Hash Mask announced by the
PIM DR is zero (no bits are set), obtain the value of PIM DR is zero (no bits are set), obtain the value of
hashvalue_Group [Section 5.2] to determine the GDR. hashvalue_Group [Section 5.2] to determine the GDR.
o If the group is in SSM mode, use hashvalue_SG [Section 5.2] to o If the group is in SSM mode, use hashvalue_SG [Section 5.2] to
determine the GDR. determine the GDR.
A simple Modulo hash algorithm is defined in this document. However, A simple Modulo Hash Algorithm is defined in this document. However,
to allow another hash algorithms to be used, a 1-octet "Hash to allow another Hash Algorithms to be used, a 1-octet "Hash
Algorithm" field is included in the DRLB-Cap Hello Option to specify Algorithm" field is included in the DRLB-Cap Hello Option to specify
the hash algorithm used by the router. the Hash Algorithm used by the router.
If different hash algorithms are advertised among the routers on a If different Hash Algorithms are advertised among the routers on a
LAN, only the outers advertising the same hash algorithm as the DR LAN, only the routers advertising the same Hash Algorithm as the DR
(as well as having the same DR priority as the DR) are eligible for (as well as having the same DR priority as the DR) are eligible for
GDR election. GDR election.
5.2. Modulo Hash Algorithm 5.2. Modulo Hash Algorithm
As part of computing the hash, the notation LSZC(hash_mask) is used As part of computing the hash, the notation LSZC(hash_mask) is used
to denote the number of zeroes counted from the least significant bit to denote the number of zeroes counted from the least significant bit
of a Hash Mask hash_mask. As an example, LSZC(255.255.128) is 7 and of a Hash Mask hash_mask. As an example, LSZC(255.255.128) is 7 and
also LSZC(FFFF:8000::) is 111. If all bits are set, LSZC will be 0. also LSZC(FFFF:8000::) is 111. If all bits are set, LSZC will be 0.
If the mask is zero, then LSZC will be 32 for IPv4, and 128 for IPv6. If the mask is zero, then LSZC will be 32 for IPv4, and 128 for IPv6.
The number of GDR Candidates is denoted as GDRC. The number of GDR Candidates is denoted as GDRC.
The idea behind the Modulo hash algorithm is in simple terms that the The idea behind the Modulo Hash Algorithm is in simple terms that the
corresponding mask is applied to a value, then the result is shifted corresponding mask is applied to a value, then the result is shifted
right LSZC(mask) bits so that the least significant bits that were right LSZC(mask) bits so that the least significant bits that were
masked out are not considered. Then this result is masked by 0xFFFF, masked out are not considered. Then this result is masked by 0xFFFF,
keeping only the last 32 bits of the result (this only makes a keeping only the last 32 bits of the result (this only makes a
difference for IPv6). Finally, the hash value is this result modulo difference for IPv6). Finally, the hash value is this result modulo
the number of GDR Candidates (GDRC). the number of GDR Candidates (GDRC).
The Modulo hash algorithm for computing the values hashvalue_RP, The Modulo Hash Algorithm for computing the values hashvalue_RP,
hashvalue_Group and hashvalue_SG is defined as follows. hashvalue_Group and hashvalue_SG is defined as follows.
hashvalue_RP is calculated as: hashvalue_RP is calculated as:
(((RP_address & RP_mask) >> LSZC(RP_mask)) & 0xFFFF) % GDRC (((RP_address & RP_mask) >> LSZC(RP_mask)) & 0xFFFF) % GDRC
RP_address is the address of the RP defined for the group and RP_address is the address of the RP defined for the group and
RP_mask is the RP Hash Mask. RP_mask is the RP Hash Mask.
hashvalue_Group is calculated as: hashvalue_Group is calculated as:
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hashvalue_SG is calculated as: hashvalue_SG is calculated as:
((((Source_address & Source_mask) >> LSZC(Source_mask)) & 0xFFFF) ((((Source_address & Source_mask) >> LSZC(Source_mask)) & 0xFFFF)
^ (((Group_address & Group_mask) >> LSZC(Group_mask)) & 0xFFFF)) % ^ (((Group_address & Group_mask) >> LSZC(Group_mask)) & 0xFFFF)) %
GDRC GDRC
Group_address is the group address and Group_mask is the Group Group_address is the group address and Group_mask is the Group
Hash Mask. Hash Mask.
5.2.1. Modulo Hash Algorithm Example 5.2.1. Modulo Hash Algorithm Examples
To help illustrate the algorithm, consider this example. Router X To help illustrate the algorithm, consider this example. Router X
with IPv4 address 203.0.113.1 receives a DRLB-List Hello Option from with IPv4 address 203.0.113.1 receives a DRLB-List Hello Option from
the DR, which announces RP Hash Mask 0.0.255.0 and a list of GDR 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, 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 203.0.113.2 and 203.0.113.1. The ordinal number assigned to those
addresses would be: addresses would be:
0 for 203.0.113.3; 1 for 203.0.113.2; 2 for 203.0.113.1 (Router X) 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 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: for Group2. Following the modulo Hash Algorithm:
LSZC(0.0.255.0) is 8 and GDRC is 3. The hashvalue_RP for Group1 with LSZC(0.0.255.0) is 8 and GDRC is 3. The hashvalue_RP for Group1 with
RP RP1 is: RP RP1 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
which matches the ordinal number assigned to Router X. Router X will which matches the ordinal number assigned to Router X. Router X will
be the GDR for Group1. be the GDR for Group1.
The hashvalue_RP for Group2 with RP RP2 is: The hashvalue_RP for Group2 with RP RP2 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 the ordinal number of router X (2). Hence, which is different from the ordinal number of router X (2). Hence,
Router X will not be GDR for Group2. Router X will not be GDR for Group2.
For IPv6 consider this example, similar to the above. Router X with
IPv6 address FE80::1 receives a DRLB-List Hello Option from the DR,
which announces RP Hash Mask ::FFFF:FFFF:0 and a list of GDR
Candidates, sorted by IP addresses from high to low: FE80::3, FE80::2
and FE80::1. The ordinal number assigned to those addresses would
be:
0 for FE80::3; 1 for FE80::2; 2 for FE80::1 (Router X).
Assume there are 2 RPs: RP1 2001:DB8::1:5678:1 for Group1 and RP2
2001:DB8::1:1234:2 for Group2. Following the modulo Hash Algorithm:
LSZC(::FFFF:FFFF:0) is 32 and GDRC is 3. The hashvalue_RP for Group1
with RP RP1 is:
(((2001:DB8::1:5678:1 & ::FFFF:FFFF:0) >> 32) & 0xFFFF % 3) =
((::1:5678:0 >> 32) & 0xFFFF % 3) = (::1:5678 & 0xFFFF % 3) = ::5678
% 3 = 2
which matches the ordinal number assigned to Router X. Router X will
be the GDR for Group1.
The hashvalue_RP for Group2 with RP RP2 is:
(((2001:DB8::1:1234:1 & ::FFFF:FFFF:0) >> 32) & 0xFFFF % 3) =
((::1:1234:0 >> 32) & 0xFFFF % 3) = (::1:1234 & 0xFFFF % 3) = ::1234
% 3 = 1
which is different from the ordinal number of router X (2). Hence,
Router X will not be GDR for Group2.
5.2.2. Limitations 5.2.2. Limitations
The Modulo Hash Algorithm has poor failover characteristics when a The Modulo Hash Algorithm has poor failover characteristics when a
shared LAN has more than two GDRs. In the case of more than two GDRs shared LAN has more than two GDRs. In the case of more than two GDRs
on a LAN, when one GDR fails, all of the groups may be reassigned to on a LAN, when one GDR fails, all of the groups may be reassigned to
a different GDR, even if they were not assigned to the failed GDR. a different GDR, even if they were not assigned to the failed GDR.
However, many deployments use only two routers on a shared LAN for However, many deployments use only two routers on a shared LAN for
redundancy purposes. Future work may define new hash algorithms redundancy purposes. Future work may define new Hash Algorithms
where only groups assigned to the failed GDR get reassigned. where only groups assigned to the failed GDR get reassigned.
5.3. PIM Hello Options 5.3. PIM Hello Options
When a PIM router sends a PIM Hello on an interface with this All PIM routers include a new option, called "Load Balancing
specification enabled, it includes a new option, called "Load Capability (DRLB-Cap)" in their PIM Hello messages.
Balancing Capability (DRLB-Cap)".
Besides this DRLB-Cap Hello Option, the elected PIM DR also includes Besides this DRLB-Cap Hello Option, the elected PIM DR also includes
a new "DR Load Balancing List (DRLB-List) Hello Option". The DRLB- a new "DR Load Balancing List (DRLB-List) Hello Option". The DRLB-
List Hello Option consists of three Hash Masks as defined above and List Hello Option consists of three Hash Masks as defined above and
also a sorted list of GDR Candidate addresses on the LAN. also a sorted list of GDR Candidate addresses on the LAN.
5.3.1. PIM DR Load Balancing Capability (DRLB-Cap) Hello Option 5.3.1. PIM DR Load Balancing Capability (DRLB-Cap) 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
skipping to change at page 10, line 44 skipping to change at page 11, line 23
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PIM DR Load Balancing Capability Hello Option Figure 3: PIM DR Load Balancing Capability Hello Option
Type: 34 Type: 34
Length: 4 Length: 4
Reserved: Transmitted as zero, ignored on receipt. Reserved: Transmitted as zero, ignored on receipt.
Hash Algorithm: Hash algorithm type. 0 for the Modulo algorithm Hash Algorithm: Hash Algorithm type. 0 for the Modulo algorithm
defined in this document. defined in this document.
This DRLB-Cap Hello Option MUST be advertised by routers on all This DRLB-Cap Hello Option MUST be advertised by routers on all
interfaces where DR Load Balancing is enabled. interfaces where DR Load Balancing is enabled.
5.3.2. PIM DR Load Balancing List (DRLB-List) Hello Option 5.3.2. PIM DR Load Balancing List (DRLB-List) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 11, line 24 skipping to change at page 12, line 4
| Source Mask | | Source Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Mask | | RP Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GDR Candidate Address(es) | | GDR Candidate Address(es) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PIM DR Load Balancing List Hello Option Figure 4: PIM DR Load Balancing List Hello Option
Type: 35 Type: 35
Length: (3 + n) x (4 or 16) bytes, where n is the number of GDR
Length: (3 + n) x (4 or 16), where n is the number of GDR
candidates. candidates.
Group Mask (32/128 bits): Mask applied to group addresses as part Group Mask (32/128 bits): Mask applied to group addresses as part
of hash computation. of hash computation.
Source Mask (32/128 bits): Mask applied to source addresses as Source Mask (32/128 bits): Mask applied to source addresses as
part of hash computation. part of hash computation.
RP Mask (32/128 bits): Mask applied to RP addresses as part of RP Mask (32/128 bits): Mask applied to RP addresses as part of
hash computation. hash computation.
All masks MUST have the same number of bits as the IP source All masks MUST have the same number of bits as the IP source
address in the PIM Hello IP header. address in the PIM Hello IP header.
GDR Address (32/128 bits): Address(es) of GDR Candidate(s) GDR Candidate Address(es) (32/128 bits): List of GDR Candidate(s)
All addresses MUST be in the same address family as the PIM All addresses MUST be in the same address family as the PIM
Hello IP header. It is RECOMMENDED that the addresses are Hello IP header. It is RECOMMENDED that the addresses are
sorted in descending order. sorted in descending order.
If the "Interface ID" option, as specified in [RFC6395], is If the "Interface ID" option, as specified in [RFC6395], is
present in a GDR Candidate's PIM Hello message, and the "Router present in a GDR Candidate's PIM Hello message, and the "Router
ID" portion is non-zero: Identifier" 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 the "Router ID". to the "Router Identifier".
+ For IPv6, the "GDR Candidate Address" will be 96 bits of + For IPv6, the "GDR Candidate Address" will be 96 bits of
zeroes followed by the 32 bit Router ID. zeroes followed by the 32 bit Router Identifier.
If the "Interface ID" option is not present in a GDR Candidate' If the "Interface ID" option is not present in a GDR Candidate'
PIM Hello message, or if the "Interface ID" option is present PIM Hello message, or if the "Interface ID" option is present
but the "Router ID" field is zero, the "GDR Candidate Address" but the "Router Identifier" field is zero, the "GDR Candidate
will be the IPv4 or IPv6 source address of the PIM Hello Address" will be the IPv4 or IPv6 source address of the PIM
message. Hello message.
This DRLB-List Hello Option MUST only be advertised by the This DRLB-List Hello Option MUST only be advertised by the
elected PIM DR. It MUST be ignored if received from a non-DR. elected PIM DR. It MUST be ignored if received from a non-DR.
The option MUST also be ignored if the hash masks are not the
correct number of bits, or GDR Candidate addresses are in the
wrong address family.
5.4. PIM DR Operation 5.4. PIM DR Operation
The DR election process is still the same as defined in [RFC7761]. A The DR election process is still the same as defined in [RFC7761].
DR that has this specification enabled on an interface advertises the The DR advertises the new DRLB-List Hello Option, which contains mask
new DRLB-List Hello Option, which contains mask values from user values from user configuration (or default values), followed by a
configuration (or default values), followed by a list of GDR list of GDR Candidate Addresses. It is RECOMMENDED that the list be
Candidate Addresses. It is RECOMMENDED that the list is sorted, from sorted, from the highest value to the lowest value. The reason for
the highest value to the lowest value. The reason for sorting the sorting the list is to make the behavior deterministic, regardless of
list is to make the behavior deterministic, regardless of the order the order in which the DR learns of new candidates. Note that, as
the DR learns of new candidates. Note that same as non-DR routers, non-DR routers, the DR also advertises the DRLB-Cap Hello Option to
the DR also advertises DRLB-Cap Hello Option to indicate its indicate its ability to support the new functionality and the type of
capability of supporting this specification and the type of its GDR GDR election Hash Algorithm.
election hash algorithm.
If a PIM DR receives a neighbor DRLB-Cap Hello Option, which contains If a PIM DR receives a neighbor DRLB-Cap Hello Option, which contains
the same hash algorithm as the DR, and the neighbor has the same DR the same Hash Algorithm as the DR, and the neighbor has the same DR
priority as the DR, PIM DR SHOULD consider the neighbor as a GDR priority as the DR, PIM DR SHOULD consider the neighbor as a GDR
Candidate and insert the GDR Candidate' Address into the list of the Candidate and insert the GDR Candidate' Address into the list of the
DRLB-List Option. However, the DR may have policies limiting which DRLB-List Option. However, the DR may have policies limiting which
GDR Candidates, or the number of GDR Candidates to include. The DR GDR Candidates, or the number of GDR Candidates to include.
would normally include itself in the list of GDR Candidates. Likewise, the DR SHOULD include itself in the list of GDR Candidates,
but it is permissable not to do so, if for instance there is some
policy restricting the candidate set.
If a PIM neighbor included in the list expires, stops announcing the If a PIM neighbor included in the list expires, stops announcing the
DRLB-Cap Hello Option, changes DR priority, changes hash algorithm or DRLB-Cap Hello Option, changes DR priority, changes Hash Algorithm or
otherwise becomes ineligibile as a candidate, the DR should otherwise becomes ineligible as a candidate, the DR SHOULD
immediately send a triggered hello with a new list in the DRLB-List immediately send a triggered hello with a new list in the DRLB-List
option, excluding the neighbor. option, excluding the neighbor.
If a new router becomes eligible as a candidate, there is no urgency If a new router becomes eligible as a candidate, there is no urgency
in sending out an updated list. An updated list SHOULD be included in sending out an updated list. An updated list SHOULD be included
in the next hello. in the next hello.
5.5. PIM GDR Candidate Operation 5.5. PIM GDR Candidate Operation
When an IGMP/MLD report is received, without this specification, only When an IGMP/MLD report is received, a Hash Algorithm is used by the
the PIM DR will handle the join and potentially run into the issues GDR Candidates to determine which router is going to be responsible
described earlier. Using this specification, a hash algorithm is for building forwarding trees on behalf of the host.
used by the GDR Candidates to determine which router is going to be
responsible for building forwarding trees on behalf of the host.
If this specification is enabled on an interface, the router MUST The router MUST include the DRLB-Cap Hello Option in all PIM Hello
include the DRLB-Cap Hello Option in all PIM Hello messages sent on messages sent on the interface. Note that the presence of the DRLB-
that interface. Note that the presence of the DRLB-Cap Option in PIM Cap Option in the PIM Hello does not guarantee that the router will
Hello does not guarantee that this router would be considered as a be considered as a GDR candidate. Once the DR election is done, the
GDR candidate. Once DR election is done, the DRLB-List Hello Option DRLB-List Hello Option is received from the current PIM DR containing
would be received from the current PIM DR on the link which would a list of the selected GDRs Candidates.
contain a list of GDRs Candidates selected by the PIM DR.
A router only acts as a GDR Candidate if it is included in the GDR A router only acts as a GDR Candidate if it is included in the GDR
Candidate list of the DRLB-List Hello Option. See next section for Candidate list of the DRLB-List Hello Option. See next section for
details. details.
5.6. DRLB-List Hello Option Processing 5.6. DRLB-List Hello Option Processing
This section discusses processing of the DRLB-List Hello Option. All This section discusses processing of the DRLB-List Hello Option,
routers MUST ignore the DRLB-List Hello Option if it is received from including the case where it was received in the previous hello, but
a PIM router which is not the DR. The option MUST only be processed not in the current hello. All routers MUST ignore the DRLB-List
by routers that are announcing the DRLB-Cap Option. Also, the Hello Option if it is received from a PIM router which is not the DR.
algorithm announced in the DRLB-Cap Option, MUST be the same as what The option MUST only be processed by routers that are announcing the
was announced by the DR. All GDR Candidates MUST use the Hash Masks DRLB-Cap Option, and only if the Hash Algorithm announced by the DR
advertised in the Option, even if they differ from those the is the same as the local announcement. All GDR Candidates MUST use
candidate was configured with. the Hash Masks advertised in the Option, even if they differ from
those the candidate was configured with. The DR MUST also process
its own DRLB-List Hello Option.
A router stores the latest option contents that was announced, if A router stores the latest option contents that was announced, if
any, and deletes the previous contents. The router MUST also compare any, and deletes the previous contents. The router MUST also compare
the new contents with any previous contents, and if there are any the new contents with any previous contents, and if there are any
changes, continue processing as below. Note that if the option does changes, continue processing as below. Note that if the option does
not pass the above checks, the below processing MUST be done as if not pass the above checks, the below processing MUST be done as if
the option was not announced. the option was not announced.
If the contents of the DRLB-List Option, the masks or the candidate If the contents of the DRLB-List Option, the masks or the candidate
list, differs from the previously saved copy, it is received for the list, differs from the previously saved copy, it is received for the
first time, or it is no longer being received or accepted, the option first time, or it is no longer being received or accepted, the option
MUST be processed as below. MUST be processed as below.
1. If the router was not included in the previous GDR list, or there 1. If the local router is included in the GDR Candidate Address(es)
was no previous GDR list, but it is included in the new GDR list, field, for each of the groups, or source and group pairs if the
the router MUST for each of the groups, or source and group pairs group is in SSM mode, with local receiver interest, the router
if the group is in SSM mode, with local receiver interest, run MUST run the Hash Algorithm to determine which of them it is the
the hash algorithm to determine which of them it is the GDR for. GDR for.
If it is not the GDR for a group, or source and group pair if
SSM, no processing is required.
If it is hashed as the GDR, it needs to build a multicast
forwarding tree.
2. If the router was included in the previous GDR list, and still is If there is no change in the GDR status, then no further
included in the new GDR list: The router MUST for each of the action is required.
groups, or source and group pairs if the group is in SSM mode,
with local receiver interest, run the hash algorithm to determine
which of them it is the GDR for.
If it was the GDR for a group, or source and group pair if If the router becomes the new GDR, then a multicast forwarding
SSM, and the new hash result chose it as the GDR, then no tree MUST be built [RFC7761].
processing is required.
If it was the GDR for a group, or source and group pair if If the router is no longer the GDR, then it uses an Assert as
SSM, earlier and now it is no longer the GDR, then it sets the
assert metric preference to maximum (0x7FFFFFFF) and the
assert metric to one less than maximum (0xFFFFFFFE), as
explained in [Section 5.7]. explained in [Section 5.7].
If it was not the GDR for a group, or source and group pair if 2. If the local router is not included in the GDR Candidate
SSM, earlier, and the new hash does not make it GDR, then no Address(es) field, or if the DRLB-List Hello Option is no longer
processing is required. included in the DR's Hello, or if the DR's Neighbor Liveness
Timer expires [RFC7761], for each of the groups, or source and
If it was not the GDR for an earlier group, or source and group pairs if the group is in SSM mode, with local receiver
group pair if SSM, and now becomes the GDR, it starts building interest, for which the router is the GDR, it uses an Assert as
multicast forwarding tree for this flow. explained in [Section 5.7].
3. If the router was included in the previous GDR list, but is not
included in the new GDR list, or there is no new GDR list: The
router MUST for each of the groups, or source and group pairs if
the group is in SSM mode, with local receiver interest do as
follows.
If it was the GDR for a group, or source and group pair if
SSM, it sets the assert metric preference to maximum
(0x7FFFFFFF) and the assert metric to one less than maximum
(0xFFFFFFFE), as explained in [Section 5.7].
If it was not the GDR, then no processing is required.
5.7. PIM Assert Modification 5.7. PIM Assert Modification
GDR changes may occur due to configuration change, due to GDR GDR changes may occur due to configuration change, due to GDR
candidates going down, and also new routers coming up and becoming candidates going down, and also new routers coming up and becoming
GDR candidates. This may occur while flows are being forwarded. If GDR candidates. This may occur while flows are being forwarded. If
the GDR for an active flow changes, there is likely to be some the GDR for an active flow changes, there is likely to be some
disruption, such as packet loss or duplicates. By using asserts, disruption, such as packet loss or duplicates. By using asserts,
packet loss is minimized, while allowing a small amount of packet loss is minimized, while allowing a small amount of
duplicates. duplicates.
When a router stops acting as the GDR for a group, or source and When a router stops acting as the GDR for a group, or source and
group pair if SSM, it MUST set the assert metric preference to group pair if SSM, it MUST set the Assert metric preference to
maximum (0x7FFFFFFF) and the assert metric to one less than maximum maximum (0x7FFFFFFF) and the Assert metric to one less than maximum
(0xFFFFFFFE). This was also mentioned in the previous section. That (0xFFFFFFFE). This was also mentioned in the previous section. That
is, whenever it sends or receives an assert for the group, it must is, whenever it sends or receives an Assert for the group, it must
use these values as the metric preference and metric rather than the use these values as the metric preference and metric rather than the
values provided by routing. This is similar to what is done for values provided by the unicast routing protocol.
AssertCancel Messages in [RFC7761], except that the metric value here
is one less.
The rest of this section is just for illustration purposes and not The rest of this section is just for illustration purposes and not
part of the protocol definition. part of the protocol definition.
To illustrate the behavior when there is a GDR change, consider the To illustrate the behavior when there is a GDR change, consider the
following scenario where there are two flows G1 and G2. R1 is the following scenario where there are two flows G1 and G2. R1 is the
GDR for G1, and R2 is the GDR for G2. When R3 comes up, it is GDR for G1, and R2 is the GDR for G2. When R3 comes up, it is
possible that R3 becomes GDR for both G1 and G2, hence R3 starts to possible that R3 becomes GDR for both G1 and G2, hence R3 starts to
build the forwarding tree for G1 and G2. If R1 and R2 stop build the forwarding tree for G1 and G2. If R1 and R2 stop
forwarding before R3 completes the process, packet loss might occur. forwarding before R3 completes the process, packet loss might occur.
On the other hand, if R1 and R2 continue forwarding while R3 is On the other hand, if R1 and R2 continue forwarding while R3 is
building the forwarding trees, duplicates might occur. building the forwarding trees, duplicates might occur.
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.
Using the above example, for G1, assume R1 and R3 agree on the new For G1, using the functionality described in this document, R1 and R3
GDR, which is R3. With the new assert behavior, R1 sets its assert determine the new GDR, which is R3. With the modified Assert
metric to the near maximum value discussed above. That will make R3, behavior, R1 sets its Assert metric to the near maximum value
which has normal metric in its Assert as the Assert winner. discussed above. That will make R3, which has normal metric in its
Assert as the Assert winner.
For G2, assume it takes a slightly longer time for R2 to find out
that R3 is the new GDR and still considers itself being the GDR while
R3 already has assumed the role of GDR. Since both R2 and R3 think
they are GDRs, they further compare their metric and IP addresses.
If R3 has the better routing metric, or the same metric but a better
tie-breaker, the result will be consistent during GDR selection. If
unfortunately, R2 has the better metric or the same metric but a
better tie-breaker, R2 will become the Assert winner and continues to
forward traffic. Shortly after when R2 finds out that it is no
longer the GDR, R2 will change to using the near maximum assert
metric. Next time R2 sends an assert message, it will lose the
assert and stop forwarding. As assert winner, R2 would send periodic
assert messages per [RFC7761].
5.8. Backward Compatibility 5.8. Backward Compatibility
In the case of a hybrid Ethernet shared LAN (where some PIM routers In the case of a hybrid Ethernet shared LAN (where some PIM routers
enable the specification defined in this document, and some do not). support the functionality defined in this document, and some do not);
o If a router which does not support this specification becomes the o If the DR does not support the new functionality, then there will
DR on the LAN, then it is the only router acting as a DR, and be no load-balancing.
there will be no load-balancing.
o If a router which does not support this specification becomes a o If non-DR routers do not support the new functionality, they will
non-DR on link, then it acts as non-DR defined in [RFC7761], and not be considered as Candidate GDRs and it will not take part in
it will not take part in any load-balancing. Load-balancing may an load-balancing. Load-balancing may still happen on the link.
still happen.
6. Manageability Considerations 6. Operational Considerations
An administrator needs to consider what the total bandwidth An administrator needs to consider what the total bandwidth
requirements are and find a set of routers that together has enough requirements are and find a set of routers that together has enough
total capacity, while making sure that each of the router can handle total capacity, while making sure that each of the routers can handle
its part, assuming that the traffic is distributed roughly equally its part, assuming that the traffic is distributed roughly equally
among the routers. Ideally, one should also have enough bandwidth to among the routers. Ideally, one should also have enough bandwidth to
handle the case where at least one router fails. Ideally all the handle the case where at least one router fails. All routers should
routers should have reachability to the sources, and RPs if have reachability to the sources, and RPs if applicable, that is not
applicable, that is not via the LAN. via the LAN.
Care must be taken when choosing what hash masks to configure. One Care must be taken when choosing what hash masks to configure. One
would typically configure the same masks on all the routers, so that would typically configure the same masks on all the routers, so that
they are the same, regardless of which router is elected as DR. The they are the same, regardless of which router is elected as DR. The
default masks are likely suitable for most deployment. The RP Hash default masks are likely suitable for most deployment. The RP Hash
Mask must be configured (the default is no bits set) if one wishes to Mask must be configured (the default is no bits set) if one wishes to
hash based on the RP address rather than the group address for ASM. hash based on the RP address rather than the group address for ASM.
The default masks will use the entire group addresses, and source The default masks will use the entire group addresses, and source
addresses if SSM, as part of the hash. An administrator may set addresses if SSM, as part of the hash. An administrator may set
other masks that masks out part of the addresses to ensure that other masks that masks out part of the addresses to ensure that
skipping to change at page 17, line 19 skipping to change at page 17, line 11
Balancing List (DRLB-List) Hello Option in the PIM-Hello Options Balancing List (DRLB-List) Hello Option in the PIM-Hello Options
registry. IANA is requested to make these assignments permanent when registry. IANA is requested to make these assignments permanent when
this document is published as an RFC. Note that the option names this document is published as an RFC. Note that the option names
have changed slightly since the temporary assignments were made. have changed slightly since the temporary assignments were made.
Also, the length of option 34 is always 4, the registry currently Also, the length of option 34 is always 4, the registry currently
says it is variable. says it is variable.
This document requests IANA to create a registry called "Designated This document requests IANA to create a registry called "Designated
Router Load Balancing Hash Algorithms" in the "Protocol Independent Router Load Balancing Hash Algorithms" in the "Protocol Independent
Multicast (PIM)" branch of the registry tree. The registry lists Multicast (PIM)" branch of the registry tree. The registry lists
hash algorithms for use by PIM Designated Router Load Balancing. Hash Algorithms for use by PIM Designated Router Load Balancing.
7.1. Initial registry 7.1. Initial registry
The initial content of the registry should be as follows. The initial content of the registry should be as follows.
Type Name Reference Type Name Reference
------ ---------------------------------------- -------------------- ------ ---------------------------------------- --------------------
0 Modulo This document 0 Modulo This document
1-255 Unassigned 1-255 Unassigned
7.2. Assignment of new hash algorithms 7.2. Assignment of new Hash Algorithms
Assignment of new hash algorithms is done according to the "IETF Assignment of new Hash Algorithms is done according to the "IETF
Review" model, see [RFC8126]. Review" model, see [RFC8126].
8. Security Considerations 8. 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 messages, so the security guaranteed by the security of PIM Hello messages, so the security
considerations for PIM Hello messages as described in PIM-SM considerations for PIM Hello messages as described in PIM-SM
[RFC7761] apply here. [RFC7761] apply here.
If the DR is subverted it could omit or add certain GDRs or announce If the DR is subverted it could omit or add certain GDRs or announce
an unsupported algorithm. If another router is subverted, it could an unsupported algorithm. If another router is subverted, it could
be made DR and cause similar issues. While these issues are specific be made DR and cause similar issues. While these issues are specific
to this specification, they are not that different from existing to this specification, they are not that different from existing
attacks such as subverting a DR and lowering the DR priority, causing attacks such as subverting a DR and lowering the DR priority, causing
a different router to become the DR. a different router to become the DR.
If for any reason, the DR includes a GDR in the announced list which
announces a different algorithm from what the DR announces, the GDR
is required to ignore the announcement, and there will be no router
acting as the DR for the flows that hash to that GDR.
If a GDR is subverted, it could potentially be made to stop If a GDR is subverted, it could potentially be made to stop
forwarding all the traffic it is expected to forward. This is also forwarding all the traffic it is expected to forward. This is also
similar today to if a DR is subverted. similar today to if a DR is subverted.
9. Acknowledgement 9. Acknowledgement
The authors would like to thank Steve Simlo and Taki Millonis for The authors would like to thank Steve Simlo and Taki Millonis for
helping with the original idea; Alia Atlas, Bill Atwood, Jake helping with the original idea; Alia Atlas, Bill Atwood, Jake
Holland, Bharat Joshi, Anish Kachinthaya, Anvitha Kachinthaya and Holland, Bharat Joshi, Anish Kachinthaya, Anvitha Kachinthaya and
Alvaro Retana for reviews and comments; and Toerless Eckert and Alvaro Retana for reviews and comments; and Toerless Eckert and
skipping to change at page 18, line 36 skipping to change at page 18, line 32
[RFC6395] Gulrajani, S. and S. Venaas, "An Interface Identifier (ID) [RFC6395] Gulrajani, S. and S. Venaas, "An Interface Identifier (ID)
Hello Option for PIM", RFC 6395, DOI 10.17487/RFC6395, Hello Option for PIM", RFC 6395, DOI 10.17487/RFC6395,
October 2011, <https://www.rfc-editor.org/info/rfc6395>. October 2011, <https://www.rfc-editor.org/info/rfc6395>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>. 2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 10.2. Informative References
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002, 3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>. <https://www.rfc-editor.org/info/rfc3376>.
skipping to change at page 19, line 15 skipping to change at page 19, line 15
[RFC4541] Christensen, M., Kimball, K., and F. Solensky, [RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol "Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping (IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>. <https://www.rfc-editor.org/info/rfc4541>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>. <https://www.rfc-editor.org/info/rfc4607>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses Authors' Addresses
Yiqun Cai Yiqun Cai
Alibaba Group Alibaba Group
Email: yiqun.cai@alibaba-inc.com Email: yiqun.cai@alibaba-inc.com
Heidi Ou Heidi Ou
Alibaba Group Alibaba Group
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