1. 1 0940_03F8_c1 NW97_US_106 Multicast Issues for Gigapop Operators David Meyer Gigapop Operators II Workshop 26 June 1998 0940_03F8_c1 NW97_US_106

2. 2 0940_03F8_c1 NW97_US_106 Introduction First Some Basic Technology Basic Host Model Basic Router Model Data Distribution Concepts What Are the Deployment Obstacles What Are the Non-technical Issues What Are the Technical Scaling Issues Agenda

3. 3 0940_03F8_c1 NW97_US_106 Agenda (Cont.) Potential Solutions (Cisco Specific) Multi-level RP, Anycast Clusters, MSDP Using Directory Services Industry Solutions BGMP and MASC Possible Deployment Scenarios References

4. 4 0940_03F8_c1 NW97_US_106 Introduction—Level Set This presentation focuses on large-scale multicast routing for Gigapops and their customers Note that the problem is essentially the same as the inter-domain multicast routing problem The problems/solutions presented are related to inter-enterprise or Gigapop deployment of IP multicast The current set of deployed technology is sufficient for enterprise environments

5. 5 0940_03F8_c1 NW97_US_106 Introduction—Why Would You Want to Deploy IP Multicast? You don’t want the same data traversing your links many times— bandwidth saver You want to join and leave groups dynamically without notifying all data sources—pay-per-view

6. 6 0940_03F8_c1 NW97_US_106 Introduction—Why Would You Want to Deploy IP Multicast? You want to discover a resource but don’t know who is providing it or if you did, don’t want to configure it— expanding ring search Reduce startup latency for subscribers

7. 7 0940_03F8_c1 NW97_US_106 Introduction—Why Would a Gigapop Want to Deploy IP Multicast? All of the previous, plus revenue potential for deploying IP multicast Initial applications Radio station transmissions Real-time stock quote service Future applications Distance learning Entertainment

8. 8 0940_03F8_c1 NW97_US_106 Basic Host Model Strive to make the host model simple When sourcing data, just send the data Map network layer address to link layer address Routers will figure out where receivers are and are not When receiving data, need to perform two actions Tell routers what group you’re interested in (via IGMP) Tell your LAN controller to receive for link-layer mapped address

9. 9 0940_03F8_c1 NW97_US_106 Basic Host Model Hosts can be receivers and not send to the group Hosts can send but not be receivers of the group Or they can be both

10. 10 0940_03F8_c1 NW97_US_106 Basic Host Model There are some protocol and architectural issues Multiple IP group addresses map into a single link-layer address You need IP-level filtering Hosts join groups, which means they receive traffic from all sources sending to the group Wouldn’t it be better if hosts could say what sources they were willing to receive from

11. 11 0940_03F8_c1 NW97_US_106 Basic Host Model There are some protocol and architectural issues (continued) You can access control sources but you can’t access control receivers in a scalable way

12. 12 0940_03F8_c1 NW97_US_106 Basic Router Model Since hosts can send any time to any group, routers must be prepared to receive on all link-layer group addresses And know when to forward or drop packets

13. 13 0940_03F8_c1 NW97_US_106 Basic Router Model What does a router keep track of? interfaces leading to receivers sources when utilizing source distribution trees prune state depending on the multicast routing protocol (e.g. Dense Mode)

14. 14 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Routers maintain state to deliver data down a distribution tree Source trees Router keeps (S,G) state so packets can flow from the source to all receivers Trades off low delay from source against router state

15. 15 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Shared trees Router keeps (*,G) state so packets flow from the root of the tree to all receivers Trades off higher delay from source against less router state

16. 16 0940_03F8_c1 NW97_US_106 Data Distribution Concepts How is the tree built? On demand, in response to data arrival Dense-mode protocols (PIM-DM and DVMRP) MOSPF Explicit control Sparse-mode protocols (PIM-SM and CBT)

17. 17 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Building distribution trees requires knowledge of where members are flood data to find out where members are not (Dense-mode protocols) flood group membership information (MOSPF), and build tree as data arrives send explicit joins and keep join state (Sparse-mode protocols)

18. 18 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Construction of source trees requires knowledge of source locations In dense-mode protocols you learn them when data arrives (at each depth of the tree) Same with MOSPF In sparse-mode protocols you learn them when data arrives on the shared tree (in leaf routers only) Ignore since routing based on direction from RP Pay attention if moving to source tree

19. 19 0940_03F8_c1 NW97_US_106 Data Distribution Concepts To build a shared tree you need to know where the core (RP) is Can be learned dynamically in the routing protocol (Auto-RP, PIMv2) Can be configured in the routers Could use a directory service

20. 20 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Source trees make sense for Broadcast radio transmissions Expanding ring search Generic few-sources-to-many-receiver applications High-rate, low-delay application requirements Per source policy from a service provider’s point of view Per source access control

21. 21 0940_03F8_c1 NW97_US_106 Data Distribution Concepts Shared trees make sense for Many low-rate sources Applications that don’t require low delay Consistent policy and access control across most participants in a group When most of the source trees overlap topologically with the shared tree

22. 22 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Non-Technical Issues How to bill for the service Is the service what runs on top of multicast? Or is it the transport itself? Do you bill based on sender or receiver, or both? How to control access Should sources be rate-controlled (unlike unicast routing) Should receivers be able to receive at a specific rate only?

23. 23 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Non-Technical Issues How to make your peers fan-out instead of you (reduce the replication factor in you own network) Closest exit versus latest entrance—all a wash How to avoid multicast from opening a lot of security holes Network-wide denial of service attacks Eaves-dropping simpler since receivers are unknown

24. 24 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Technical Issues Source tree state will become a problem as IP multicast gains popularity When policy and access control per source will be the rule rather than the exception Group state will become a problem as IP multicast gains popularity 10,000 three member groups across the Internet

25. 25 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Technical Issues Hopefully we can upper bound the state in routers based on their switching capacity

26. 26 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Technical Issues Gigapop customers are telling us they don’t want to depend on another customer’s (or gigapop) RP Do we connect shared trees together? Do we have a single shared tree across domains? Do we use source trees only for inter-domain groups?

27. 27 0940_03F8_c1 NW97_US_106 Deployment Obstacles— Technical Issues Customers are telling us that the unicast and multicast topologies won’t be congruent across domains Due to physical/topological constraints Due to policy constraints We need a inter-domain routing protocol that distinguishes unicast versus multicast policy

28. 28 0940_03F8_c1 NW97_US_106 How to Control Multicast Routing Table State in the Network? Fundamental problem of learning group membership Flood and Prune DVMRP PIM-DM Broadcast Membership MOSPF DWRs Rendezvous Mechanism PIM-SM BGMP

29. 29 0940_03F8_c1 NW97_US_106 Rendezvous Mechanism Why not use sparse-mode PIM? Where to put the root of the shared tree (the RP) Third-party RP problem If you did use sparse-mode PIM Group-to-RP mappings would have to be distributed throughout the Internet

30. 30 0940_03F8_c1 NW97_US_106 Rendezvous Mechanism Lets try using sparse-mode PIM for inter-domain multicast Look at four possibilities Multi-level RP Anycast clusters MSDP Use directory services

31. 31 0940_03F8_c1 NW97_US_106 Connect Shared Trees Together—Multi-Level RP Idea is to have a hierarchy of shared trees Level-0 RPs are inside of domains They propagate joins from routers to a Level-1 RP that may be in another domain All level-0 shared trees get connected together via a Level-1 RP If multiple Level-1 RPs, iterate up to Level-2 RPs

32. 32 0940_03F8_c1 NW97_US_106 Connect Shared Trees Together—Multi-Level RP Problems Requires PIM protocol changes If you don’t locate the Level-0 RP at the border, intermediate PIM routers think there may be two RPs for the group Still has the third-party problem, there is ultimately one node at the root of the hierarchy Data has to flow all the way to the highest- level RP

33. 33 0940_03F8_c1 NW97_US_106 Connect Shared Trees Together—Anycast Clusters Share the burden of being an RP among service providers Each RP in each domain is a border router Build RP clusters at interconnect points (or dense-mode clouds) Group allocation is per cluster and not per-user or per-domain

34. 34 0940_03F8_c1 NW97_US_106 Connect Shared Trees Together—Anycast Clusters Closest border router in cluster is used as the RP Routers in a domain will use the domain’s RP Provided you have an RP for that group range at an interconnect point If not, you use the closest RP at the interconnect point (could be RP in another domain)

35. 35 0940_03F8_c1 NW97_US_106 Connect Domains Together— MSDP If you can’t connect shared trees together easily, then don’t Multicast Source Discovery Protocol Different paradigm Rather than getting trees connected, get sources known to all trees Sounds non-scalable, but the trick is in the implementation

36. 36 0940_03F8_c1 NW97_US_106 Connect Domains Together— MSDP An RP in a domain has a MSDP peering session with an RP in another domain Runs over TCP Source-Active (SA) messages are sent to describe active sending sources in a domain Logical topology is built for the sole purpose to distribute SA messages

37. 37 0940_03F8_c1 NW97_US_106 Connect Domains Together— MSDP How it works Source goes active in PIM-SM domain It’s packets get PIM registered to domain’s RP RP sends SA message to it’s MSDP peers Other MSDP peers forward to their peers away from the originating RP If a peer in another domain has receivers for the group the source is sending to, it joins the source (Flood-and-Join model)

38. 38 0940_03F8_c1 NW97_US_106 Connect Domains Together— MSDP There is no shared tree across domains Therefore each domain can depend solely on it’s own RP (no third-party problem) SA state is not stored at each MSDP peer You could encapsulate data in SA messages for low-rate bursty sources You could have SA caching peers to speed up join latency

39. 39 0940_03F8_c1 NW97_US_106 Use Directory Services You can use directory services to: Enable a single shared tree across domains Enable use of source tree only and avoid using a single shared tree across domains

40. 40 0940_03F8_c1 NW97_US_106 Use Directory Services How it works with a single shared tree across domains Put RP in client’s domain Optimal placement of the RP if the domain had a multicast source or receiver active Policy for RP is consistent with policy for domain’s unicast prefixes Use directory to find RP address for a given group

41. 41 0940_03F8_c1 NW97_US_106 Use Directory Services For example Receiver host sends IGMP report for 224.1.1.1 First-hop router performs DNS name resolution on 1.1.1.224.pim.mcast.net An A record is returned with the IP address of RP First-hop router sends PIM join message towards RP

42. 42 0940_03F8_c1 NW97_US_106 Use Directory Services All routers get consistent RP addresses via DNS When dynamic DNS is widely deployed it will be easier to change A records In the mean time, use loopback addresses on routers and move them around in your domain

43. 43 0940_03F8_c1 NW97_US_106 Use Directory Services When domain group allocation exists, a domain can be authoritative for a DNS zone 1.224.pim.mcast.net 128/17.1.224.pim.mcast.net

44. 44 0940_03F8_c1 NW97_US_106 Use Directory Services Another approach—avoid using shared trees all together Build PIM-SM source trees across domains Put multiple A records in DNS to describe sources for the group 1.0.2.224.sources.pim.mcast.net IN CNAME dmm-home IN CNAME dino-home dmm-homeINA171.69.58.81 dino-homeINA171.69.127.178

45. 45 0940_03F8_c1 NW97_US_106 Standards Solutions Ultimate scalability of both routing and group allocation can be achieved using BGMP/MASC Use BGP4+ (MBGP) to deal with non-congruency issues

46. 46 0940_03F8_c1 NW97_US_106 Border Gateway Multicast Protocol (BGMP) Use a PIM-like protocol that runs between domains (BGP equivalent for multicast) The protocol builds a shared tree of domains for a group So we can use a rendezvous mechanism at the domain level Shared tree is bi-directional Root of shared tree of domains is at root domain

47. 47 0940_03F8_c1 NW97_US_106 Border Gateway Multicast Protocol (BGMP) Runs in routers that border a multicast routing domain Runs over TCP like BGP Joins and prunes travel at domain hops Can build unidirectional source trees MIGP tells the borders about group membership

48. 48 0940_03F8_c1 NW97_US_106 Multicast Address Set Claim (MASC) How does one determine the root domain for a given group? Group prefixes are temporarily leased to domains They are allocated out of a service provider’s allocation which in turn get from upstream provider

49. 49 0940_03F8_c1 NW97_US_106 Multicast Address Set Claim (MASC) Claims for group allocation resolve collisions Group allocations are advertised across domains Lots of machinery for aggregating group allocations

50. 50 0940_03F8_c1 NW97_US_106 Multicast Address Set Claim (MASC) Tradeoff between aggregation and anticipated demand for group addresses Group prefix allocations are not assigned to domains—they are leased Application must be written to know that group addresses may go away Work in progress

51. 51 0940_03F8_c1 NW97_US_106 Using BGP4+ (MBGP) for Non-Congruency Issues Multiprotocol extensions to BGP4— RFC 2283 MBGP allows you to build a unicast RIB and multicast RIB independently with one protocol Can use the existing or new BGP peering topology MBGP carries unicast prefixes of multicast capable sources

52. 52 0940_03F8_c1 NW97_US_106 Possible Deployment Scenarios Environment: Multiple customers multicast peer at a Gigapop Deployment proposal Each customer puts their own administered RP attached to the Gigapop That RP as well as all border routers run MBGP The interconnect runs dense-mode PIM Each customer runs PIM-SM/DM internally

53. 53 0940_03F8_c1 NW97_US_106 Possible Deployment Scenarios What about multiple interconnect points between Gigapop customers? If multiple Gigapop customers connect at different interconnect points, they can multicast peer for any groups as long as their respective RPs are collocated on the same Gigapop (and the interconnect is Dense mode)

54. 54 0940_03F8_c1 NW97_US_106 Possible Deployment Scenarios What if all RPs are not at the same interconnect point? Use MSDP so the sources known to the interconnect with RPs can tell the RPs at other interconnects where to join

55. 55 0940_03F8_c1 NW97_US_106 Possible Deployment Scenarios Use a group range that depends on DNS for rendezvousing or building trees Customers decide which domains will have RPs Customers decide which groups will use source trees and don’t have to administer RPs Customers administer DNS databases