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Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net 1
Multicast in BGP/MPLS VPNs and VPLS
draft-raggarwa-l3vpn-mvpn-vpls-mcast-01.txt
Rahul Aggarwal
2Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
Authors Rahul Aggarwal (Juniper) Thomas Morin (France Telecom) Luyuan Fang (AT&T) Yakov Rekhter (Juniper) Anil Lohiya (Juniper) Tom Pusateri (Juniper) Lenny Giuliano (Juniper) Chaitanya Kodeboniya (Juniper)
3Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
Agenda IP Multicast in VPLS – Issues with existing
proposals
Design Objective
Solution
4Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
IP Multicast in VPLS This talk is about IP multicast data traffic
in VPLS
It is not about VPLS control traffic
It is also not about flooding to all PEs (by the ingress PE) in the VPLS for unknown destinations for unicast traffic
5Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
Current VPLS proposals:
“Virtual Private LAN Service” (draft-ietf-l2vpn-vpls-bgp-02.txt)
“Virtual Private LAN Services over MPLS” (draft-ietf-l2vpn-vpls-ldp-05.txt )
Limitations of these solutions for IP multicast in VPLS…
6Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
VPLS Reference Model
PE 1
CE-B2
CE-B3
PE 3
PE 2
PE 4
VPLS ASite 2
CE -A1
CE-B1
CE-A2
CE-A4
CE-A3
VPLS BSite 1
VPLS BSite 2
VPLS ASite 4
Emulated Emulated LANLAN
for VPLS Bfor VPLS B
VPLS BSite 3
VSI-A
VSI-A
VSI-A
VSI-A
VSI-B
VSI-B
VSI-B
Emulated Emulated LAN for VPLSLAN for VPLS
AA
VPLS ASite 3
VPLS ASite 1
VSI – Virtual Switch Instance
No PIM peering between CEs and PEsNo PIM peering among PEs
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Forwarding VPLS multicast traffic within the service provider – Emulated LAN
Ingress replication of the IP multicast packet for a given VPLS by the ingress PE
The packet is sent over the Emulated LAN associated with the VPLS
Emulated LAN is realized by ingress replication – use collection of the existing (unicast) LSPs
• From ingress PE to egress PEs
• No additional state (beyond what is require by unicast) on P routers
• May result in sending multiple copies of the same multicast packet over a given service provider link
8Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
Emulated LAN Ingress Replication: example
PE 1
CE-B2
CE-B3
PE 3
PE 2PE 4
VPLS ASite 3
CE -A1
CE-B1
CE-A2
CE-A4
CE-A3VPLS BSite 1
VPLS BSite 2
VPLS BSite 3
VSI-A
VSI-A
VSI-A
VSI-B
VSI-B
VSI-B
VPLS ASite 2
VPLS ASite 1
Links
S1G1
G1
G1
(S1, G1) traffic to Site 2(S1, G1) traffic to Site 3
The same (multicast) packet traverses link 3 times
VPLS ASite 4
VSI-A
G1
(S1, G1) traffic to Site 4
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Sending multicast traffic to sites with no receivers: example
PE 1
CE-B2
CE-B3
PE 3
PE 2PE 4
VPLS ASite 3
CE -A1
CE-B1
CE-A2
CE-A4
CE-A3VPLS BSite 1
VPLS BSite 2
VPLS BSite 3
VSI-A
VSI-A
VSI-A
VSI-B
VSI-B
VSI-B
VPLS ASite 2
VPLS ASite 1
Links
S1G1
G1
G1
(S1, G1) traffic to Site 2(S1, G1) traffic to Site 3
VPLS ASite 4
VSI-A
(S1, G1) traffic to Site 4
Multicast traffic for VPLS A extends to CE-A4,even though it has no receivers for G1
Site 4 has no receivers for G1
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Sending multicast traffic to sites with no receivers
As long as PE does not keep track of IP multicast receivers within each site of a given VPLS, PE has to send IP multicast traffic to all the sites within that VPLS
As long as the ingress PE sends (multicast) traffic to all the sites within a VPLS, it is possible that the traffic will be delivered to the sites of that VPLS that have no receivers for the traffic
Suboptimal use of the service provider bandwidth due to sending IP multicast traffic to sites with no receivers is further compounded by the use of ingress replication for Emulated LAN
11Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
How to avoid sending multicast traffic to sites with no receivers – PIM/IGMP snooping
Well-known approach used by Ethernet switches
• An Ethernet switch determines whether a particular port has receivers for a given (S,G) by snooping on the PIM/IGMP messages received over that port
• Requires to disable PIM Join suppression In the context of VPLS, PE has to snoop on PIM/IGMP messages
received from:
• all sites of that VPLS (directly) connected to the PE, • Can not be avoided AND
• all the remote PEs that have members of that VPLS• Huge overhead particularly given the periodic nature of PIM
Joins
Just like with Ethernet switches, PIM/IGMP snooping in the context of VPLS requires to disable PIM Join suppression by VPLS customers
12Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
PIM snooping : example
PE 1
CE-B2
CE-B3
PE 3
PE 2PE 4
VPLS ASite 3
CE -A1
CE-B1
CE-A2
CE-A4
CE-A3VPLS B
Site 1
VPLS BSite 2
VPLS BSite 3
VSI-A
VSI-A
VSI-A
VSI-B
VSI-B
VSI-B
VPLS ASite 2
VPLS ASite 1
Links
S1G1
G1
G1
(S1, G1) traffic to Site 2(S1, G1) traffic to Site 3
VSI-A
PE1 does not send (S1,G1) traffic to Site 4, as PE1 notices that Site 4 has no receivers for G1
PIM Join (S1, G1) from Site 2PIM Join (S1, G1) from Site 3
VPLS ASite 4 Site 4 has no receivers for G1
13Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
Multicast in 2547 VPNs vs multicast in VPLS
Focus on minimizing service provider bandwidth usage by (a) minimizing the amount of (multicast) traffic replication within the service provider, and by (b) avoiding sending traffic to the PE routers with no receivers
• At the expense of additional state within the service provider
Focus on minimizing state in the service provider routers by eliminating any multicast-related state in the P routers
• At the expense of additional bandwidth usage within the service provider
Why the tradeoffs for multicast in 2547 VPNs are NOT the same as the tradeoffs for multicast in VPLS ?
2547 VPNs: VPLS:
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Solution
The existing solutions are clearly not sufficient for IP multicast support in VPLS
Draft-raggarwa-l3vpn-mvpn-vpls-mcast-00.txt• Work in progress• Aims to overcome the issues that have been
pointed out A scalable MVPN/VPLS multicast architecture
• Overcomes issues with prior solutions• This presentation talks only about VPLS
Reuse procedures across MVPN/VPLS multicast as much as possible
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VPLS IP MulticastAvoid Flooding
IGMP/PIM snooping between PE and directly connected sites
• Not performed for remote sites Convert periodic PIM C-Joins snooped from a directly
connected CE to reliable protocol messages across the SP core
• Eliminates the overhead of snooping periodic PIM messages from remote sites
• This can be done using either PIM or BGP
• Draft points out the information elements The C-Join/Prune has to be sent to all the PEs in the VPLS if
the PE sending the C-Join/Prune does not know the route to the C-Source
• A database of C-Source to the PE that the C-source is behind needs to be maintained to eliminate this overhead
16Copyright © 2004 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net
VPLS IP MulticastData Plane
Flexible/Scalable Transport of Customer Multicast Data Packets through the SP core
SP Multicast Trees• Allow multiple VPLSs to share a single
SP multicast tree• Can be set up using PIM or P2MP MPLS
TE LSPs or another P2MP technology Ingress Replication
• Has its applicability
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Aggregate Trees Allow one SP multicast Tree to be shared across
multiple VPLSs Can be setup using PIM-SM or PIM-SSM or P2MP
MPLS TE or another P2MP technology Requires an inner label to demultiplex a particular
VPLS
• ‘Upstream’ label allocation by the root of the tree A flexible tool to reduce state in the SP network State in the SP network doesn’t grow proportional
to the number of VPLSs
• Similar to unicast in VPLS or unicast in 2547
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Aggregate Trees… Use BGP signaling Mapping of an Aggregate Tree to VPLSs
associated with the Tree are signaled by the root using BGP
• Leaves of the tree are PEs belonging to all the VPLSs mapped to the tree: discovered using the auto-discovery mechanism (eg. BGP)
• Applicable to both BGP and LDP based VPLS The draft points out the information elements to
be exchanged Encoding open to discussion
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Aggregate Trees: Example
PE 1
CE-B2
CE-B3
PE 3
PE 2PE 4
VPLS ASite 3
CE -A1
CE-B1
CE-A2
CE-A4
CE-A3VPLS BSite 1
VPLS BSite 2
VPLS BSite 3
VSI-A
VSI-A
VSI-A
VSI-B
VSI-B
VSI-B
VPLS ASite 2
VPLS ASite 1
Links
S1G1
G1
G1
The same (multicast) packet traverses the link only once
VPLS ASite 4
VSI-A
G1
Aggregate Tree for VPLS A and VPLS B
Upstream label for VPLS A
Upstream label for VPLS B
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Aggregate Data Trees A flexible tool to create separate trees for a set of
customer groups to avoid flooding Allow one SP multicast Tree to be shared across
multiple (C-S,C-Gs) that may belong to different VPLSs
• Leaves of the tree are (C-S, C-Gs) discovered from the C-Join information
Setup using BGP signaling by the root
• Applicable to both LDP and BGP based VPLS Requires an inner label to de-multiplex a particular
VPLS
• ‘Upstream’ label allocation by the root of the tree
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On P2MP MPLS TE Certainly applicable to setting up SP
multicast tree
• Potential TE benefits
Aggregate Tree and Aggregate Data Trees
Procedures in the draft are independent of the SP P2MP technology and apply to P2MP MPLS TE as well