MULTICAST BGP EXTENSION

First Question you need to know is why?
why we need BGP extension for Multicast?
the answer is simply we need to connect and multicast between two or more Domains "Autonomous systems" and BGP uses unicast to connect to its neighbors, so you have to use AF for Multicast in order to enable the multicast via BGP.


we will work on the topology below:

Important things to have before configuring mBGP-Multicast extension are:
1.FULL IGP routing table exchanged between routers and reach-ability
2. Interfaces on order Router facing EBGP neighbor should be passive for IGP
3. run EBGP border Routers or neighboring AS
4. run iBGP and make sure from Full BGP neighbor-ship and routes exchange
till the last router in your AS but using Confederations or Route-Reflectors in our case we will
use R6 and R1 from each side to be point of reflection for incoming iBGP routes learned from Border
Routers {don't forget to make border routers to act as next-hop for all the iBGP neighbors
5. configure BGP address-family for multicasting and this will require activating commands
6.redistribution point will be the border routers in order to bring reachability between
the two domains
7. use peer groups when needed to ease up configuration
8. choose the PIM mode you have been tasked to use Standard or Cisco
9. sparse mode is the common mode used and enable MSDP
NOTE: MSDP is used because RP's are in two different domains and in order to learn about sources in other domains we will use MSDP.
10. Verify your configuration by joining one router to multicast group and ping it from the remote site
11. use #show bgp ipv4 multicast summary to see the activated neighbors
12. use #show ip mroute x.x.x.x for the group
13. use #show ip rpf
14. use #show ip pim rp mapping  to verify your RP in each domain