BGP Multicast

Multicast BGP
Some Cases don’t want uni-cast traffic to route the same direction as multicast traffic, multicast BGP is basically a way to change the Reverse Path Forwarding Check without having to do static multicast routes everywhere

For multicast transit over the internet all hops must run multicast

• What if the RPF check for a multicast source is via a unicast only peer?
• Multicast BGP solves this by separating unicast RPF and multicast RPF
• Multicast BGP advertises source networks for purpose of RPF check
• By the way, Multicast BGP does not replace PIM
• Multicast BGP preferred over uni-cast protocols for multicast RPF check
• Like a static multicast route but dynamic
•     Doesn’t require a separate routing protocol, only BGP extensions

       How Multicast BGP Works

•       BGP peers negotiate Multicast Address Family during capabilities exchange
•       Peers advertises NLRI under Multicast Address Family
•       Network statement just like uni-cast
•       All normal BGP rules apply
•        When multicast traffic is received, MBGP learned routes are preferred over uni-cast

        Configuration

       Note - *** eBGP (which is AS- 20 lowest AS number) might want to use. If you want to use iBGP  (  which is AS-200), route will prefer IGP which is lower AS than iBGP and RPF check will fail. This point, you might want to change AS number lager than iBGP  **** 

•        Router (config) # router bgp 200
•        Router (config-router) # neighbor 10.35.35.5 remote-as 1
•        Router (config-router) # address-family ipv4 unicast
•        Router (config-router) # neighbor 10.35.35.5 activate
•        Router (config-router) # address-family ipv4 multicast
•        Router (config-router) # neighbor 10.35.35.5 activate
•        Router (config-router-af) # network 10.45.45.0 mask 255.255.255.0

       BGP Multicast LAB

     R3 CONFIGURATION

       R3(config-router-af)#do sh run | section router bgp

       router bgp 2

       bgp log-neighbor-changes 

       neighbor 10.35.35.5 remote-as 1 

       !

       address-family ipv4 

       neighbor 10.35.35.5 activate

       exit-address-family

       ! 

       address-family ipv4 multicast

       network 10.12.12.0 mask 255.255.255.0

       network 10.45.45.0 mask 255.255.255.0

       neighbor 10.35.35.5 activate

       exit-address-family

       R3(config-router-af)#

    

       R5 CONFIGURATION

       R5#show run | section router bgp

       router bgp 1 

       bgp log-neighbor-changes

       neighbor 10.35.35.3 remote-as 2

       !

       address-family ipv4

       neighbor 10.35.35.3 activate 

       exit-address-family 

       ! 

       address-family ipv4 multicast

       network 2.2.2.2 mask 255.255.255.255 

       network 10.45.45.0 mask 255.255.255.0 

       neighbor 10.35.35.3 activate 

       exit-address-family

   ROUTER 5 RPF CHECK ROUTE

•      Even though R5 unicast route through R3 but RPF route go through R4.

      Check route from R5 to R1 multicast and uni-cast routing   

     REFERENCE

         https://ine.com/
   https://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfmbgp.html
   https://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfmbgp.pdf