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Sunday, May 8, 2011

CCIE Notes - Multicast

Multicast notes:
  • class D - ( –
  • reserved (like rfc 1918) – ( -
  • Administratively Scoped Block  –
  1. hello’s are sent every 30 sec to
  2. loopback – ip ospf point-to-point for RPF check
  3. (S,G) source tree / shortest path tree / source
    (*,G) shared tree / any source
  4. holdtime = 3.5x the hello
  5. highest IP wins DR
  6. lowest IP wins designated querier
  7. rp-address (unicast) must be advertised in unicast IGP
  8. mtrace to group address to see the reverse path
  9. traffic is always sent to the group address, never from.
  10. the source ip is always a unicast ip address, never a mcast address.
  11. igmp = router to client (automatically enabled with PIM)
  12. pim = router to router ( relies on unicast routing domain, do make sure you have full igp connectivity)
  13. sparse-mode – explicit join ( no traffic unless uyou request it) need’s an RP.
  14. dense-mode – implicit join (gets all traffic unlexx you don’t want it), flood and prune
  15. enabe mcast = ip multicast-routing (distributed on 3560)
  16. (*,G) don’t care about the source.  (S,G) knows the source
    • incoming null / outgoing null – does not know the source.
  17. Enable PIM on the shortest path to the Rp or you will get RFP failures.
  18. switching from a shared tree (*,G) to a  shortest path tree (S,G) = SPT switchover
  19. if theRPF fails the packet is dropped.
    • ping
    • sh ip mroute count
    • debup ip packet
    • ip mroute to rpf failure interface.
  20. RP
      • auto -rp
        • ip pim sparse-dense
        • ip pim send-rp-announce loopback scope 16
          ip pim send-rp-discovery scope 16
        • p pim autorp listener – use when you have sparse-mode interfaces/all sparse mode router.
        • fallback to dense mode is he default, to prevent it use : ip pim dm-fallback.
        • (announce) and
        • Candidate RPs advertize their willingness to be an RP via “RP-announcement” messages. These messages are periodically sent to a reserved well-known group (CISCO-RP-ANNOUNCE).
        • RP mapping agents join group and map the RPs to the associated groups. The RP mapping agents advertise the authoritative RP-mappings to another well-known group address (CISCO-RP-DISCOVERY). All PIM routers join and store the RP-mappings in their private cache.
        • deny statements – the groul ill be negatively cached and run int dense mode.
        • control updates with ip multicast boundry
        • For the Auto-RP with Multiple RPs scenario, no load balancing is provided, and, when an RP changes, convergence is normally on the order of 3 minutes.
      • Bootstrap router
        • ip pim sparse-mode
          ip pim bsr-candidate
          ip pim rp-candidate
        • use hash to load balance
        • multiples overlapping RP’s = highest priority wins
        • control updates with ip pim bsr-border
    • static – ip pim rp-address – you need this on all the mcast devices.
      • override – will override AUTORP or BSR rp mappings.
    • dynamic – auto-rp (cisco prorietary)  or BSR
  21. ip pim NBMA = use on hub in a FR network, to bypass split-horizon behavior.
  22. GRE is the duct tape of routing!!!  makse your tunnel interfaces passive.
  23. troubleshootin mcast:
    • 1  int s0/0 no ip mroute-cache -2- debup ip mpacket
    • debup ip pim
    • sh ip pim nei | rp | rp mapping | interface
    • sh ip pin int f0/0 detail
    • debup ip pim auto-rp <-shows you what RP is filtered.
    • sh run | in ip pim|int
    • keyword search under ip pim command reference
  24. ip helper-map
    • convert from mcast group to broadcast
      • ip multi helper-map 111
      • acecss-list 111 oer udp host a eq 39000
  25. anycast – 2 RP’s with the same IP address’
    • r1
      int lo0
      ip add
      int lo1
      ip add
      ip msdp peer connect-sour loo1
      ip msdp originator-id loo1
      ip pim rp-address [acl]
      int lo0
      ip add
      int lo1
      ip add
      ip msdp peer connect-sour loo1
      ip msdp originator-id loo1
      ip pim rp-address [acl]

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