Symptom
L2 multicast split-horizon group does not work properly on physical AC interfaces when there is a split-horizon group configuration change on an interface. If the split-horizon group is changed on an egress interface, that interface will no longer receive traffic. If the split-horizon group is changed on an ingress interface, traffic may not egress some interfaces.
Note that this only affects physical interfaces and sub-interfaces. Bundles, pseudowire, and pseudowire headend interfaces are not affected.
Conditions
This only affects physical interfaces and sub-interfaces. Bundles, pseudowire, and pseudowire headend interfaces are not affected.
This only affects L2 multicast (igmp snooping or mld snooping).
This only occurs when the split-horizon group config (under l2vpn bridge-domain) is changed (added or removed) when doing igmp/mld snooping.
Workaround
There is a simple workaround for this issue. Follow these steps when doing a split-horizon group configuration change:
1) First remove the interface from the L2VPN bridge-domain configuration; commit the change
2) Add the interface back to the L2VPN bridge-domain, along with the split-horizon group config (if adding it), or without the split-horizon group config (if removing it). Commit the change.
Further Problem Description
Recovery:
If you get into a state where you changed the split-horizon group config without doing the workaround, and traffic is not egressing properly, you can recover by removing the interface from the L2VPN bridge-domain (and commit), and adding it back (with the split-horizon config if desired).
