Internet DRAFT - draft-liu-bess-evpn-mcast-bw-quantity-df-election
draft-liu-bess-evpn-mcast-bw-quantity-df-election
BESS Working Group Yisong Liu
Internet Draft China Mobile
Intended status: Standards Track M. McBride
Expires: August 21, 2021 Futurewei
Z. Zhang
ZTE
J. Xie
Huawei
Feb 21, 2021
Multicast DF Election for EVPN based on bandwidth or quantity
draft-liu-bess-evpn-mcast-bw-quantity-df-election-03
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Abstract
Ethernet Virtual Private Network (EVPN, RFC7432) is becoming
prevalent in Data Centers, Data Center Interconnect (DCI) and
Service Provider VPN applications. When multi-homing from a CE to
multiple PEs, including links in an EVPN instance on a given
Ethernet Segment, in an all-active redundancy mode, [RFC7432]
describes a basic mechanism to elect a Designated Forwarder (DF),
and [RFC8584] improves basic DF election by a HRW algorithm. [I-
D.ietf-bess-evpn-per-mcast-flow-df-election] enhances the HRW
algorithm for the multicast flows to perform DF election at the
granularity of (ESI, VLAN, Mcast flow). This document specifies a
new algorithm, based on multicast bandwidth utilization and
multicast state quantity, in order for the multicast flows to elect
a DF.
Table of Contents
1. Introduction ................................................ 3
1.1. Requirements Language .................................. 4
1.2. Terminology ............................................ 4
2. Solution .................................................... 4
2.1. DF Election Based on Bandwidth ......................... 5
2.2. DF Election Based on State Qunatity .................... 5
2.3. Inconsistent Timing between Multi-homed PEs ............ 5
2.4. Increase or Decrease of Multi-homed PEs ................ 6
2.4.1. Decrease of Multi-homed PEs ....................... 6
2.4.2. Increase of Multi-homed PEs ....................... 7
3. BGP Encoding ................................................ 7
3.1. DF Election Extended Community ......................... 7
3.2. Multicast DF Extended Community ........................ 8
4. Security Considerations ..................................... 8
5. IANA Considerations ......................................... 9
6. References .................................................. 9
6.1. Normative References ................................... 9
6.2. Informative References ................................. 9
7. Acknowledgments ............................................ 10
Authors' Addresses ............................................ 11
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1. Introduction
Ethernet Virtual Private Network (EVPN [RFC7432]) solutions are
becoming prevalent in Data Centers, Data Center Interconnect (DCI)
and Service Provider VPN applications. When multi-homing from a CE
to multiple PEs, with links in an EVPN instance on a given Ethernet
Segment (ES), in an all-active redundancy mode, [RFC7432] defines
the role of Designated Forwarder (DF) as the node that is
responsible to forward multicast flows.
Per [RFC7432], the basic method of DF election is specified. The
same ES is sorted in ascending order according to the IP address of
the EVPN peer. The PE set is generated, and then the number of PEs
is modulo according to the VLAN. The modulo value is equal to the
position of the PE in the PE set. The election is the primary DF of
the corresponding VLAN, and the other PEs are elected as standby.
[RFC8584] defines extended community attributes for DF elections,
which can be extended to use different DF election algorithms and
would be used for PEs in a redundancy group to reach a consensus as
to which DF election procedure is desired. A PE can notify other
participating PEs in a redundancy group about its DF election
algorithm by signaling a DF election extended community along with
the ES route. The document also improves the basic DF election by a
HRW algorithm.
[I-D.ietf-bess-evpn-per-mcast-flow-df-election] proposes a method
for DF election by enhancing the HRW algorithm, adding the source
and group address of the multicast flow as hash factors, and
extending the types 4 and 5 of the extended community of the DF
election for (S, G) and (*, G) types for different multicast flows.
The source and group address is introduced as new elements to HRW
algorithm, and the PE with the largest weight is selected as the DF
of the multicast flow.
However, the relationship between the bandwidth of the multicast
flows and the link capacity of different PEs, to the same CE device,
is not considered in any of the current DF election algorithms. This
may result in severe bandwidth utilization of different links due to
different bandwidth usage of multicast flows. This document
specifies a new algorithm for multicast flow DF election based on
multicast bandwidth or multicast state quantity and extends the
existing extended community defined in [I-D.ietf-bess-evpn-df-
election-framework].
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
CE: Customer Edge equipment
PE: Provider Edge device
EVPN: Ethernet Virtual Private Network
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links, then that
set of links is referred to as an 'Ethernet segment'.
IGMP: Internet Group Management Protocol
MLD: Multicast Listener Discovery
PIM: Protocol Independent Multicast
2. Solution
In the DF election calculation, the bandwidth weight of each multi-
homed link of the PE is added, and the bandwidth occupation of the
multicast flows is calculated and divided into two scenarios:
* The specific bandwidth value of the multicast flow exists, and the
ratio of the current multicast flow bandwidth value to the link
bandwidth weight is calculated according to the bandwidth weight of
each multi-homed link, and the link with the smallest ratio is
elected as the new multicast flow DF.
* The specific bandwidth value of the multicast flow does not exist,
and the ratio of the current multicast flow state quantity to the
link bandwidth weight is calculated according to the bandwidth
weight of each multi-homed link, and the link with the smallest
ratio is elected as the new multicast flow DF.
In particular, if there are multiple PEs with the same calculated
ratio, the DF is elected according to the method of maximum
bandwidth weight of the link or maximum IP address of the EVPN peer.
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Since [I-D.ietf-idr-link-bandwidth] defines the link bandwidth
extended community, it can be reused to transfer the link bandwidth
value of the local ES to other multi-homed PEs, so that each PE can
calculate the bandwidth weight ratio of each link of the ES in
advance.
2.1. DF Election Based on Bandwidth
Each PE obtains the link bandwidth values of the other multi-homed
PEs in the same EVPN instance on a given ES according to the
extended community of the Link bandwidth, and calculates the link
bandwidth weight ratio, for example W1:W2:...:Wn for N multi-homed
PEs.
When the CE sends an IGMP or PIM join to one of the PEs, like PE1,
PE1 advertises the PE2, PE3, ... and PEn by the EVPN IGMP/PIM Join
Synch route defined in [I-D.ietf-bess-evpn-igmp-mld-proxy] and [I-
D.skr-bess-evpn-pim-proxy]. If PE2, PE3, ... or PEn receives an IGMP
or PIM join, the procedure will be the same.
Each PE calculates the ratio of the current multicast flows
bandwidth to the link bandwidth weight. The one PE in PE1, PE2, ...
and PEn, which has the smallest ratio, is elected as the DF of the
new multicast flow. When the smallest ratios of more than one PE are
the same, the PE with the maximum bandwidth weight of the link or
the maximum EVPN peer IP address is elected as the DF.
2.2. DF Election Based on State Qunatity
The procedure is almost the same as described in section 2.1. The
only difference is that each PE calculates the ratio of the current
number of multicast states instead of the bandwidth to the link
bandwidth weight because of lacking specific bandwidth value of the
multicast flows.
2.3. Inconsistent Timing between Multi-homed PEs
As a result of the same multicast join, only one of the multi-homed
PEs can receive the multicast join message and advertise the EVPN
Join Synch route (Type 7). The other PEs need to install the new
multicast join state according to the received Synch route.
The inconsistent processing timing of the same multicast group
joining process between PEs may cause electing different DFs. For
example:
* Multicast group G1, G2, and G3 join packets are sent from the CE
to PE1, PE2 and PE3.
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* PE1 calculates the DF of G1, while PE2 calculates the DF of G2,
and PE calculates the DF of G3, and at this moment each PE has not
received the EVPN Join Synch route.
* PE1, PE2 and PE3 select the link on the same ES to the CE using
the algorithm as described in section 2.1 or 2.2, and the same DF
may be elected for G1, G2, and G3.
* After receiving the EVPN Join Synch route sent by PE2, PE1 may
calculate the DF of G2 as PE3, which is inconsistent with the
calculation result of PE2.
The DF calculation results of the PEs are inconsistent, which may
result in multiple flows or traffic interruptions of the same
multicast flow state. Therefore, EVPN Join Synch routes need to
carry elected DF information in the route advertisement as the
extended community called Multicast DF Extended Community, which can
make the DF information for a given multicast flow state between PEs
consistent. The actual effect is that the PE that receives the
multicast join packet completes the calculation of the DF election
and notifies other PEs on the same ES.
2.4. Increase or Decrease of Multi-homed PEs
2.4.1. Decrease of Multi-homed PEs
When one of the multi-homed PEs on the same ES fails or is shut down
for maintenance reasons, because the other PEs have received the
synch routes of all the multicast flows, the multicast flows
destined to the failed PE need to be in a specific order (for
example, the group and source address ascending order) to reassign
the DF. The DF election calculation based on the multicast flows
bandwidth, or the number of multicast states, is completed by one of
the specified multi-homing PEs, and the specified calculated PE can
be selected according to the link bandwidth weight value or the IP
address of the EVPN peer. The specified PE needs to advertise each
DF election result of the multicast flow that belongs to the
original faulty PE to the other multi-homed PEs that belong to the
same ES by the EVPN Join Synch route carrying the Multicast DF
Extended Community.
If a new multicast join is received in the above calculation
process, the DF election calculation of the new multicast flow is
still completed by the PE receiving the multicast join packet.
Similarly, the PE needs to advertise the DF information to other
multi-homed PEs belonging to the same ES by the EVPN Join Synch
route carrying the Multicast DF Extended Community.
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2.4.2. Increase of Multi-homed PEs
One multi-homing PE of the same ES is added, and no active
adjustment can be performed. The DF of the subsequent new multicast
flow is elected according to the algorithm of this document. The new
multicast flow must be preferentially assigned to the new PE, and
finally the multicast flows on the PEs of the same ES are
approximately equalized.
If active adjustment is required, consider calculating the ratio
using the algorithm as described in section 2.1 and 2.2. Each time
the multicast entries in the PE, whose ratio of the existing multi-
homed PE is the largest, are migrated to the new PE. The multicast
entries are migrated in descending order of multicast flow bandwidth
or in ascending order of the group and source address until the
ratio of the new PE is greater than the existing smallest ratio of
other multi-homed PEs.
The calculation of the active adjustment is still performed by one
specific PE among the multi-homed PEs. The specified calculated PE
can be selected according to the link bandwidth weight value or the
IP address of the EVPN peer.
After the new PE is started, in the synchronization process of all
the multicast entries of other multi-homed PEs, the existing
multicast join packet may be received on the new PE. To avoid having
the existing multicast join appear as a new multicast join, and
recalculating the DF and notifying the other PEs belonging to the
same ES, it is necessary to start a timer to suppress the
synchronization process from the new PE to other existing PE's. The
timer range should also be configured.
3. BGP Encoding
3.1. DF Election Extended Community
[RFC8584] defines an extended community, which would be used for
multi-homed PEs to reach a consensus as to which DF election
procedure is desired. A PE can notify other participating PEs its DF
election capability by signaling a DF election extended community
along with Ethernet-Segment Route (Type-4). The current document
extends the existing extended community defined in [RFC8584]. This
document defines a new DF type.
o DF type (1 octet) - Encodes the DF Election algorithm values
(between 0 and 255) that the advertising PE desires to use for the
ES.
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* Type TBD1: Based on bandwidth of multicast flow DF
election(detailed in this document)
* Type TBD2: Based on quantity of multicast flow state DF
election(detailed in this document)
3.2. Multicast DF Extended Community
This document defines a new extended community in EVPN Type 7 route
to notify other multi-homed PEs the elected DF of a given multicast
flow. The new extended community is called Multicast DF Extended
Community and it belongs to the transitive extended community. The
type is to be assigned. It is used to carry DF information of a
given (S,G) or (*,G) multicast flow selection. The role of this
extended community has been described in sections 2.3 and 2.4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=TBD3 | Reserved | DF Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DF IP Address(Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type is 0x06 as registered with IANA for EVPN Extended Communities
o Sub-Type: TBD3
o DF Length: the length of the DF IP Address field, 4 octets for
IPv4 address, 16 octets for IPv6 address
o DF IP Address: the elected DF IP address of the given (S,G) or
(*,G) route in the EVPN type 7 route
4. Security Considerations
For general EVPN Security Considerations, see [RFC7432].
TBD
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5. IANA Considerations
TBD
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7432] A. Sajassi, Ed., R. Aggarwal, N. Bitar, A. Isaac, J.
Uttaro, J. Drake, and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, February 2015
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[RFC8584] J. Rabadan Ed., S. Mohanty, Ed., A. Sajassi, J. Drake, K.
Nagaraj and S. Sathappan, " Framework for Ethernet VPN
Designated Forwarder Election Extensibility ", RFC8584,
April 2019.
[I-D.ietf-bess-evpn-per-mcast-flow-df-election] Ali Sajassi,
Mankamana Mishra, Samir Thoria, Jorge Rabadan and John
Drake, " Per multicast flow Designated Forwarder Election
for EVPN ", August 2020, work-in-progress, draft-ietf-
bess-evpn-per-mcast-flow-df-election-04.
[I-D.ietf-idr-link-bandwidth] P. Mohapatra and R. Fernando, " BGP
Link Bandwidth Extended Community ", March 2018, expired,
draft-ietf-idr-link-bandwidth-07.
[I-D.ietf-bess-evpn-igmp-mld-proxy] Ali Sajassi, Samir Thoria, Keyur
Patel, John Drake and Wen Lin, "IGMP and MLD
Proxy for EVPN", January 2021, work-in-progress, draft-
ietf-bess-evpn-igmp-mld-proxy-06.
[I-D.skr-bess-evpn-pim-proxy] J. Rabadan, Ed., J. Kotalwar, S.
Sathappan, Z. Zhang and A. Sajassi, "PIM Proxy in EVPN
Networks", October 2017, expired, draft-skr-evpn-bess-pim-
proxy-01.
6.2. Informative References
TBD
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7. Acknowledgments
The authors would like to thank the following for their valuable
contributions of this document:
TBD
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Authors' Addresses
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Mike McBride
Futurewei Inc.
Email: michael.mcbride@futurewei.com
Zheng(Sandy) Zhang
ZTE Corporation
Email: zhang.zheng@zte.com.cn
Jingrong Xie
Huawei Technologies
Email: xiejingrong@huawei.com
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