How to provide Inter-domain multicast routing by club56

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									How to provide Inter-domain
    multicast routing?


  Computer Science 6390 – Advanced Computer Networks
                        PIM-SM
                   Dr. Jorge A. Cobb
                         MSDP
                         MBGP
PIM-SM
   Note that PIM-SM is a good candidate
     • Receivers are usually sparsely located
   What we have seen thus far should work
    • No need to do many changes for the Inter-domain
    • We have only assumed a unicast “next-hop”
   However a single shared-tree may be expensive
     • What if only one receiver, one sender (in same domain) and
       RP is many domains away?

   Solution: one shared tree in each domain!
     • Each domain has a RP
                                 2
One RP per Domain
                                   Domain E

                                        RP

                                              r
                      Domain C

                          RP

   Domain B

      RP


                                   RP

                                 Domain D

               RP
           s
               Domain A


                           3
How to find each source
   The receiver joins the tree of its local RP as before
   Sources send data to their local RP
    •   Note: these two RP could be different!

   How can the RP at E (where receiver is) learn about
    the source at A?
    •   Use the Multicast Source Discovery Protocol (MSDP)

   MSDP runs in the RP at each domain
   When a new source joins the RP:
    •   MSDP informs all other domain RP’s of the new source in
        its domain

                                   4
MSDP Flooding
   Each MSDP router (i.e., each RP) maintains a TCP
    connection with the MSDP router (i.e. the RP) of each
    neighboring domain.
   When the RP detects a new source in its domain,
     • It sends a “source active” SA message to all its MSDP
       peers
     • This message is flooded to all MSDP routers (i.e. to all
       RP’s)
     • How is the flooding done?
         • Use a form of RPF, i.e., use the implicit broadcast
           tree of unicast
         • If a RP receives a SA message from its next hop
           (next domain) to the source of the SA message,
           then it is accepted and send to all peers.
                               5
     Broadcast tree of Domain A
                                              Domain E
MSDP Peers

Unicast Path                                       RP


                                 Domain C

                                     RP

               Domain B

                  RP


                                              RP

                                            Domain D

                          RP

                          Domain A


                                      6
     MSDP Overview
                                                                       Domain E
MSDP Peers
Source Active           SA                                                  RP
Messages
                                                           SA
                                         Domain C

                                              RP
                                                                      SA
                Domain B SA                             SA


                        RP

                                         SA                            RP


                             SA                  SA Message
                                                                     Domain D
                                              192.1.1.1, 224.2.2.2
                                  RP
      Register               s
 192.1.1.1, 224.2.2.2             Domain A


                                               7
Joining the SPT of the Source
   The RP at E, since it has a receiver, may join the
    SPT of the source
    •   A join is sent along the path to the DR of the source
    •   This causes a path to be built in the SPT of S

   The DR of the receiver may also join the SPT of the
    source




                                8
      MSDP Overview
                                                                       Domain E
MSDP Peers
Source Active           SA                                                  RP
Messages
                                                           SA                            r
Multicast Traffic                        Domain C

                                              RP                                 Join (*, 224.2.2.2)
                                                                      SA
                    Domain B SA                         SA


                        RP

                                         SA                            RP


                             SA                                      Domain D
                                                 SA Message
                                              192.1.1.1, 224.2.2.2
                                  RP
      Register               s
 192.1.1.1, 224.2.2.2             Domain A


                                               9
      MSDP Overview
                                                    Domain E
MSDP Peers

Multicast Traffic                                        RP

                                                               r
                                       Domain C

                                           RP

                    Domain B

                       RP


                                                    RP

                                                  Domain D

                                RP
                            s
                                Domain A


                                            10
Multiprotocol BGP
   Not all domains will support multicast
   Note that join messages are sent via unicast
   What if they traverse a domain where routers don’t support
    multicast?
   We need separate routing for regular unicast messages and
    multicast join messages
   MBGP is the same as BGP, except it provides more than one
    route
     • MBGP may support many “protocols”
     • Provide one route to the destination for each of these
       protocols
     • E.g. “multicast” would be one “protocol”

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