March 2010 IETF 77, MPLS WG 1

Carrying PIM-SM in ASM mode Trees over P2MP mLDP LSPs

draft-rekhter-pim-sm-over-mldp-01.txt

Y. Rekhter, Juniper Networks

R. Aggarwal, Juniper Networks

N. Leymann, Deutsche Telekom

March 2010 IETF 77, MPLS WG 2

Problem Statement

• For some applications it may be desirable to map IP multicast trees to P2MP LSPs, when such trees pass through a MPLS domain

• When the P2MP LSPs are signaled using P2MP LDP, draft-wijnands-mpls-mldp-in-band-signaling describes how to map PIM-SM in SSM mode trees to P2MP LDP LSPs

• draft-wijnands-mpls-mldp-in-band-signaling does not describe how to map PIM-SM in ASM mode trees to P2MP LDP LSPs

• Draft-rekhter-pim-sm-over P2MP LDP describes how to map PIM-SM in ASM mode trees to P2MP LDP LSPs

March 2010 IETF 77, MPLS WG 3

Solution (1)

• Use a combination of BGP and P2MP LDP to map PIM-SM in ASM mode trees to P2MP LSP

• Use BGP Source Active (SA) A-D routes described in draft-ietf-l3vpn-2547bis-mcast-bgp

• Two options– Option 1 – does not transit IP multicast shared trees

over the MPLS network– Option2 – enables transit of IP multicast shared trees

over the MPLS network

March 2010 IETF 77, MPLS WG 4

Solution (2)

• Each IP multicast source tree is mapped one-to-one to a P2MP LSP in the MPLS network– Just like draft-wijnands-mpls-mldp-in-band-

signaling – This type of service works well if the number

of LSPs that are created is under control of the MPLS network operator, or if the number of LSPs for a particular service are known to be limited in number.

March 2010 IETF 77, MPLS WG 5

Comparison with BGP MVPN

• BGP MVPN procedures as described in draft-ietf-l3vpn-2547bis-mcast can be used to map IP multicast trees to P2MP LSPs– Both for PIM-SM in SSM mode and PIM-SM in ASM mode

• BGP MVPN procedures also support the ability to aggregate multiple IP multicast trees to one P2MP LSP in the MPLS network.

• The procedures of draft-rekhter-pim-sm-over-mldp-01.txt can be viewed as an optimization, compared to the reuse of the BGP MVPN procedures– Maybe beneficial in some deployment scenarios

March 2010 IETF 77, MPLS WG 6

Option 1

• IP multicast shared trees do not transit over the MPLS network

• BGP Source Active routes are used by a RP to advertise active multicast sources

• A LSR that has downstream (*, G) IP multicast state creates (S, G) IP multicast state based on the presence of a BGP SA A-D route for (S, G)– The LSR maps the (S, G) state to a P2MP LDP LSP

• Traffic flows only on a source tree over the MPLS network– There is no shared tree to source tree switch over the

MPLS network

March 2010 IETF 77, MPLS WG 7

Option 2

• IP multicast shared trees transit over the MPLS network• A LSR maps downstream (*, G) IP Multicast state into

P2MP LDP using new transit shared tree TLVs which embed the RP address instead of the source address

• BGP Source Active routes are used to force all LSRs to switch from shared tree to source tree– Once a single LSR joins the source tree– Prunes sources that are reachable over the MPLS network off

the shared tree

• BGP SA A-D routes are originated by a LSR that:– receives a P2MP LDP LSP for the given source and for a group

in the ASM range– is on the path to reach the source via an IP multicast interface

March 2010 IETF 77, MPLS WG 8

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