Junos OS

Hi,

Do I must configure the rfp table to use inet.2 if I use MBGP ?

According to the therory : "MBGP allows us to advertise routes from and place routes into the inet.2 routing table."

Regards,

DaBo$$

If peers are not MBGP, you cannot export routes from inet.2 to them, only routes in the inet.0 routing table. Routes in inet.2 can be sent only to MBGP peers, since they are sent with subaddress family information that identifies them as routes to multicast sources. The inet.2 table should be a subset of the routes that you have in inet.0, since it is unlikely that you would have a route to a multicast source to which you could not send unicast traffic.

The inet.2 routing table is used to keep the unicast routes that are used for multicast reverse-path-forwarding checks. You automatically get an inet.2 routing table when you configure MBGP (by setting NLRI to any). The additional reachability information learned by MBGP from the NLRI multicast updates are placed in inet.2.

Hi Ahmad,

Thank your for your reply but this is what I can read on the Juniper documentation.

I would like to know why use MBGP family inet multicast if the rpf table is inet.0. According to me, if the rpf use inet.0, I don't need to use MBGP for multicast...Is it correct ?

thank you for your help...

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DaBo$$

Hi Daboss,

"According to me, if the rpf use inet.0, I don't need to use MBGP for multicast...Is it correct ? "

Yes Correct as for as RPF checks are concerned.

Well, RPF checks are performed only on unicast addresses to find the upstream interface for the multicast source or RP.

The routing table used for RPF checks can be the same routing table used to forward unicast IP packets, or it can be a separate routing table used only for multicast RPF checks. In either case, the RPF table contains only unicast routes, because the RPF check is performed on the source address of the multicast packet, not the multicast group destination address, and a multicast address is forbidden from appearing in the source address field of an IP packet header. The unicast address can be used for RPF checks because there is only one source host for a particular stream of IP multicast content for a multicast group address, although the same content could be available from multiple sources.

Further If the same routing table used to forward unicast packets is also used for the RPF checks, the routing table is populated and maintained by the traditional unicast routing protocols such as BGP, OSPF etc. If a dedicated multicast RPF table is used, this table must be populated by some other method.

Hi Ahmad,

Again, thank your for your reply. To conclude, what is the role of MBGP for multicast, expect of exchanging the rpf table ?

Regards,

DaBo$$

MBGP is used so your multicast traffic can take a different path than your unicast traffic. The main advantage of MBGP is that an internet can support noncongruent unicast and multicast topologies. When the unicast and multicast topologies are congruent,

MBGP can support different policies for each.

MBGP provides a scalable policy based interdomain routing protocol. Two path attributes, MP_REACH_NLRI and MP_UNREACH_NLRI have been introduced in BGP4+. These new attributes create a simple way to carry two sets of routing information—one for unicast routing and one for multicast routing. The routes associated with multicast routing are used to build the multicast distribution trees.

If you can write me an email @ masoodnt10@gmail.com ;  I can send you a ppt presentation describing MBPG multicast in depth.

Hi Ahmad !

Thanks to you I definitely understand the relations between MBGP/inet.2/Multicast.

Thank you for your help.

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DaBo$$