Multicast
Static multicast routes (mroutes) explicitly define the expected
upstream path (either a next-hop IP address or an incoming interface) for
RPF checks on arriving multicast traffic,
overriding the default RPF behavior.
When a multicast packet arrives, the router performs the RPF check against the
matching mroute in the dedicated multicast routing table
(MRIB), rather than looking up
the standard unicast routing table
(RIB).
If the packet arrives via the expected upstream path defined in the MRIB, the RPF check passes, and the packet is forwarded toward the multicast receivers. Otherwise, the packet is dropped.
Administrators build the MRIB by manually configuring mroutes. The ZEBRA
routing daemon uses these entries exclusively for multicast RPF lookups. ZEBRA
neither evaluates mroutes in the unicast RIB nor installs them into the
kernel FIB.
Configuration
Use the following commands to configure mroutes for a specific multicast
source subnet.
Note
Because mroutes bypass standard forwarding logic, they may cause
unpredictable network behavior. Use mroutes with caution; in most cases,
overriding the default RPF check is unnecessary.
Next-hop mroutes
Configure the next-hop IP address for the specified source subnet.
When multicast traffic originates from this subnet, the router expects it to arrive from the upstream neighbor at the specified IP address.
You can configure multiple next-hop IP addresses for the same source subnet.
Example:
set protocols static mroute 192.0.2.0/24 next-hop 203.0.113.1
Configure the administrative distance for the mroute via the specified next-hop IP address.
Mroutes with a lower administrative distance are prioritized over
mroutes with a higher distance.
The allowed range is 1 to 255.
Example:
set protocols static mroute 192.0.2.0/24 next-hop 203.0.113.1 distance 50
Disable the mroute via the specified next-hop IP address.
This command temporarily deactivates the mroute while preserving the
configured subnet, next-hop, and distance parameters.
Example:
set protocols static mroute 192.0.2.0/24 next-hop 203.0.113.1 disable
Interface mroutes
Configure the valid interface for the specified source subnet.
When multicast traffic originates from this subnet, the router expects it to arrive on the specified interface.
You can configure multiple interfaces for the same source subnet.
Example:
set protocols static mroute 192.0.2.0/24 interface eth0
Configure the administrative distance for the mroute via the specified interface.
Mroutes with a lower administrative distance are prioritized over
mroutes with a higher distance.
The allowed range is 1 to 255.
Example:
set protocols static mroute 192.0.2.0/24 interface eth0 distance 30
Disable the mroute via the specified interface.
This command temporarily deactivates the mroute while preserving the
configured subnet, interface, and distance parameters.
Example:
set protocols static mroute 192.0.2.0/24 interface eth0 disable