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Multicast routing failed because multicast router port was not detected properly.

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TitleMulticast routing failed because multicast router port was not detected properly.
Symptoms
Multicast routing failed. Port connected to multicast router is not detected as a router port.
Environment
  • EXOS
  • All EXOS platforms
  • Multicast routing
Cause
When IGMP snooping is enabled then EXOS will send multicast traffic to router ports and ports were IGMP joins were received.
Multicast router port selection described in following article:
Why is a port seen as an igmp snooping router port.

When ipmc lookup key configured as group-vlan ("configure forwarding ipmc lookup-key group-vlan") switch will only store group and VLAN info not the source. If there are more then one sender on the same VLAN to the same group (like with PIM and also when using OSPF) only the first one gets configured in hardware, and the 2nd and others will not hit cache miss so these packets will not be copied to the CPU and port will not get programmed as a router port.

This can lead to fail of multicast routing and forwarding.
Resolution
To resolve the issue ipmc lookup key should be configured as (S,G,V)
configure forwarding ipmc lookup-key source-group-vlan
Workarounds:
1) configure router port statically:
configure igmp snooping vlan <vlan_name> ports <port_number> add static router
2) Use ACL to copy interesting packets to CPU.
Additional notes

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