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Basic Interdomain Multicast w/o MSDP

Load inter-as.multicast.msdp.init.cfg

#IOS-XE
config replace flash:inter-as.multicast.msdp.init.cfg
 
#IOS-XR
configure
load bootflash:inter-as.multicast.msdp.init.cfg
commit replace
y

On R2, enable multicast, PIM, and join the group (*, 239.1.1.1). On R4, send traffic to to 239.1.1.1. R4 should receive a reply from R2. Do not use MSDP to achieve this.

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Answer

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Explanation

Inter-domain multicast for ASM generally requires MSDP. However, this lab demonstrates an alternative to MSDP. By using the IGMP static-group command, the sending domain can forward the traffic out the interface to the receiving domain.

First, R2 joins group (*, 239.1.1.1). R10 is the RP for this domain, so the RP tree is only built from R2 to R10.

Next, R4 starts sending, but R9 does not notify R10 of active sources, because they are not running MSDP. As a workaround, R9 can use static-group on the interface connecting to R6 to unconditionally forward the traffic out that interface.

R9 adds this interface to the OIL for (*, 239.1.1.1):

Next, R4 starts sending and R9 forwards the traffic to R6. However, R6 realizes that the traffic is not sourced from the directly connected subnet, so it does not Register the traffic with R10. Instead, we can run dense-mode on R6 and configure R6 to proxy a PIM Register for received traffic. This was originally a way to bridge together a dense-mode and sparse-mode domain, but this tool can also be used in this context to achieve basic inter-domain multicasting.

Now when R4 sends, R6 registers this with R10. R10 can now join the SPT (11.4.13.4, 239.1.1.1):

Traffic is now working:

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