An mroute is a multicast traffic flow, a (Source,
Group) entry used for forwarding multicast traffic). By default, forwarding
mroutes (with a valid RPF incoming interface) are timed out if data
for them is not received for 210 seconds. However, you can specify
an mroute as permanent by using the ipv6 multicast-routing permanent-mroute command.
ipv6
multicast-routing permanent-mroute
Use to specify that any newly created mroutes that match
the specified access-list do not time out.
Using this command does not change existing mroutes.
Permanent mroutes are removed if a topology change occurs
that affects the mroute.
Permanent mroutes may be removed due to certain protocol
actions (for example, PIM sparse mode switching from shared to shortest
path tree).
Outgoing interface lists of permanent mroutes may change
due to protocol actions.