All things related to multicast

[Pekka Savola <>]

This is an old thread, but for the record...

On Wed, 25 Jun 2008, Bill Owens wrote:
> > The general rule is that multicast static routes are only needed when
> > your multicast needs to take a different path through the network than
> > your unicast does.. That goes for default multicast routes OUT of a
> > network and host/network specific routes IN to a network.
>
> Yes, if you are running Cisco routers. They're happy to use unicast 
> routes for RPF. However, Juniper will not (though it may be possible to 
> override that policy in the config).

By default, Cisco IOS uses both unicast and multicast routing table.

By default, JunOS uses only the unicast routing table (inet.0 and 
inet6.0).  It can be configured to use a different routing table, but just 
one, and typically that's done -- AFAIK all major academic networks use 
only inet.2 and inet6.2.  In that case you'll need to specify that direct, 
important static, aggregate, etc. routes get put to both inet.[02] and 
inet6.[02] routing tables.

Because only one routing table is used, this means that it is not possible 
to use multicast through inet.2 and inet6.2 using backbones unless you 
advertise multicast SAFI in BGP.  (Cisco IOS also supports some forms of 
BGP address family translations.)

So, in practise a default route is sufficient, but you'll need to 
advertise your address space in MP-BGP as both unicast and multicast. 
Non-MP-MGP advertisement or simple unicast MP-BGP advertisement is 
insufficient.

Pekka