PIM Boundaries using MSDP
Last updated
Last updated
Load multicast.multi.domain.init.cfg
The group of routers circled on the left should be a PIM sub-domain. Traffic for multicast group 239.10.0.0/24 should not leak out this domain.
Configure R6 and R9 as anycast RPs using BSR. Use MSDP to prevent multicast traffic for 239.10.0.0/24 from leaking outside the sub-domain.
Now that we are familiar with MSDP, we can revisit our “intra-IGP multi-domain PIM” problem. PIM domains, for ASM, are essentially bound by a group of routers sharing the same RP mapping information. In previous solutions, we attempted to block the propagation of RP information between our PIM sub domains. This prevents multicast traffic from working for certain group ranges between domains.
Now that we are familiar with MSDP, we can implement this functionality in a more elegant way. All RPs in the entire topology simply run Anycast RP. This provides HA for the RP. In addition, MSDP must be used for Anycast RP. We can filter which groups we send SA messages for, to enforce domain boundaries. Whatever groups an RP sends SA messages for become inter-domain multicast capable. Any groups the RP does not send SA messages for bounds the multicast traffic to that local domain.
For this to work correctly, all routers in a subdomain must use a single RP. For this reason, we increase the cost of XR4’s links to the other domain, so that routers such as R7 use R6 as the closest Anycast RP node.
Next, besides implementing normal Anycast RP configuration, we just instruct R6 to only send SAs for groups other than the groups which must stay local to the subdomain.
On R2 and R4, we join groups 239.10.0.1 and 239.20.0.1:
Now R1 pings these groups. Traffic for 239.10.0.1 does not generate an SA on R6, due to the ACL associated with the redistribute command. R9 never learns of the (R1, 239.10.0.1) entry and R4 never receives the traffic:
R1 then pings 239.20.0.1. R6 does send an SA for this (S, G) entry to R9. R9 is then able to join the (S, G), and R4 receives the traffic:
