1. Multicast in L3VPNs Bruce Davie 1 bsd@cisco.com draft-ietf-l3vpn-2547bis-mcast-03.txt 1. Not a draft co-author, or a multicast expert

2. Overview Aiming to encourage more involvement in multicast L3VPN work by providing user-friendly overview of problem space Focus more on problems that the current proposed solutions Hard questions will be deflected to draft authors –Likewise questions such as “why did you choose to design it that way?” Attempts to make me look ignorant will be frowned upon

3. 1 draft-rosen-vpn-mcast-08.txt Agenda Recap of current (deployed) state (draft-rosen 1 ) –See also draft-raggarwa-l3vpn-2547-mvpn-00.txt, draft-ycai-mboned-mvpn-deploy-00.txt Enhancements/changes in L3VPN WG draft –Supporting multiple tree types –Aggregation –Carrying customer multicast routing in BGP –Inter-AS improvements Note Well: WG draft is a superset of draft-rosen –i.e. deployed solutions will not be obsoleted by new draft

4. L3VPN Multicast—Motivation Customers with IP multicast traffic would like to use MPLS VPN services RFC 2547/4364 only addresses unicast As usual, multicast makes the problem harder –Difficult to achieve same scalability as unicast

5. Multicast VPN—Current Deployments Based on draft-rosen-vpn-mcast-08.txt Many similarities to unicast, and some differences CE-routers maintain PIM adjacency with PE-router only –Similar concept to 2547/4364 VPNs P-routers do not hold (S, G) state for individual customers –Unlike unicast, there is some per-customer state in P-routers PE-routers exchange customer routing information using PIM –Contrast to BGP for unicast Customer multicast group addresses need not be unique –Same as 2547/4364

6. Multicast VPN—Current State (2) Multicast domain is a set of multicast-enabled VRFs (mVRFs) that can send multicast traffic to each other –e.g., VRFs associated with a single customer Maps all (S, G) that can exist in a particular VPN to a single (S, G) group in the P-network –This is the Multicast Distribution Tree (MDT) –Amount of P-state is a function of # of VPNs rather than # of (S, G)s of all customers –This is not as good as unicast, but better than the alternative Mapping is achieved by encapsulating C-packet into P-packet using GRE

7. Customer B Default MDT 239.192.10.2 Customer B CE PE Customer B CE PE Default Multicast Distribution Tree PE routers build a default MDT in the global table for each mVRF using standard PIM procedures All PEs participating in the same mVPN join the same Default MDT Every mVRF must have a Default MDT MDT group addresses are defined by the provider –Unrelated to the groups used by the customer Data MDTs may be created for high BW sources

8. Default Multicast Distribution Tree Default MDT is used as a permanent channel for PIM control messages and low bandwidth streams Access to the Default MDT is via a Multicast Tunnel Interface A PE is always a root (source) of the MDT A PE is also a leaf (receiver) to the MDT rooted on remote PEs Customer B Default MDT 239.192.10.2 Customer B CE PE Customer B CE PE Multicast Tunnel Interface Customer B Default MDT 239.192.10.2 Root Leaf

9. Limitations of draft-rosen At least one multicast tree per customer in core –No option to aggregate multicast customers on one tree Multicast traffic is GRE (not MPLS) encapsulated –Bandwidth and encaps/decaps cost –Operational cost—different mcast and unicast data planes PIM the only fully described way to build core trees –Can’t leverage p2mp RSVP-TE, mLDP PE-PE exchange of C-routes using per-customer PIM instances Inter-AS challenges

10. PMSI: P-Multicast Service Interface New terms introduced to decouple tree from service A PE delivers packet to PMSI, then all the required PEs will get than packet and known which MVPN it belongs to Three types of PMSI –MI-PMSI: Multipoint Inclusive, all → all All PEs of an MVPN can transmit to all PEs –UI-PMSI: Unidirectional Inclusive, some → all Unidirectional, selected PEs can transmit to all PEs –Selective: S-PMSI, some → some Unidirectional, selected PEs can transmit to selected PEs

11. Types of Multicast Trees Inclusive: contains all the PEs for a given MVPN Selective: contains only a subset of PEs of a given MVPN Aggregate –Carries traffic for more than one MVPN –May be either inclusive or selective

12. Supporting Multiple Tree Types A PMSI is scoped to a single MVPN PMSI is instantiated using a tunnel (or set of tunnels) Tunnels may be: –PIM (any flavor) –MPLS (mLDP or p2mp RSVP-TE) –Unicast tunnels with ingress PE replication Can map multiple PMSIs onto one tunnel (aggregation) Encaps a function of tunnel, not service Single provider can mix and match tunnel types

13. Mappings to Old Terminology Default MDT –MI-PMSI, instantiated by PIM Shared Tree or set of PIM Source Trees Data MDT –S-PMSI, instantiated by PIM Source Tree New terminology helpful in: –Describing the complete set of options –Allowing multiple instantiations of same service, without changing service spec

14. Autodiscovery The process of discovering all the PEs with members in a given MVPN Similar to RFC4364, but: –New address family MCAST-VPN –Contains address of the originating PE –Contains tunnel attribute to specify what sort of tunnel (e.g. PIM-SSM, mLDP, etc.) can be supported by this PE, and whether aggregation is supported May contain a tunnel ID Can also be used to discover set of PEs interested in a given group (to enable S-PMSI creation)

15. Aggregation Conflicting goals – Scale: Minimize P-router state → Use as few trees as possible – Optimality: Send traffic at most once on each link, and only to PEs that need it → Use a tree for each customer multicast group Solution: lots of options – Draft-rosen has one MDT per VPN, and optional data MDT for high BW or sparse customer groups – New draft also allows a tunnel to be shared among multiple mVPNs Better aggregation, less optimality Requires a de-multiplexing field (e.g., MPLS label) – Utility of aggregation depends on amount of “congruence” and traffic volume

16. PE-PE Routing Exchange In draft-rosen, C-PIM instances exchange PIM messages over the MDT as if it were a LAN –Per-customer PIM peering among the PEs –By contrast, one BGP instance carries all customer unicast routes among PEs –PIM Hellos can be eliminated, but Join/Prunes remain In new draft, BGP is proposed, as in unicast –New AFI/SAFI –Advertisement contains essentially the same info as a PIM join or prune (source, group, PE sending the message) –RDs are used to disambiguate customer multicast group and source addresses –BGP route reflectors may be used

17. Inter-AS Old (draft-rosen) approach: tunnel spans multiple ASes –Undesirable fate-sharing, must agree on tunnel type New draft allows another approach: may “splice” tunnels from different ASes –Allows each AS to build its tunnels independently of other ASes –Scaling now independent of number of PEs in other ASes

18. Inter-AS Overlay Tunnel For a given MVPN, each AS independently builds an intra-AS tunnel In addition, an “overlay tunnel” that spans multiple ASes is built Each PE announces its MVPN membership info to the ASBRs with iBGP An ASBR announces the AS MVPN membership to other ASBRs (in other ASes) using eBGP This enables an AS-level spanning tree to be built among the set of ASes with members in this MVPN –Inter-AS tunnels spliced to intra-AS tunnels

19. Inter-AS Tunnels ASBR1 ASBR2 Customer A ASBR3 Customer A Intra-AS tunnels Inter-AS tunnels

20. Other issues RPF establishment –PEs need to know who their RPF PE is for a given route Duplicate detection –Multihomed sites and switching from shared to source tree can lead to a PE getting duplicate packets –draft proposes means to address this C-RP Engineering –RP location in customer sites may cause “hairpin” –PEs may act as “outsourced” C-RPs –PEs may speak MSDP to C-RPs

21. Conclusions WG draft builds on rosen draft without obsoleting it: –Support for more tree types, including PIM variants, mLDP, RSVP-TE –Separation of service and mechanism –Aggregation support –More Inter-AS options with improved independence –Possibility to use BGP for C-route exchange