OSPF Multicast

Unanswered Question
May 5th, 2005

Dear all,

I found on CCNP Selfstudy for BSCI the following:

NBMA ----Unicast

Point-to-Multipoint ----Multicast

Broadcast ----Multicast

Point-to-Multipoint NB ----Unicast

Point-to-Point ----Multicast

Does the table correct?

But then I found in the following document that 'Point-to-Multipoint sends unicast packets after the 2-way state'. Does it mean that P-t-MP default is multicast and then changes to Unicast after 2-way established?

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0f.shtml

Thanks in advance.

Br,

Sam

I have this problem too.
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Josef Oduwo Thu, 05/05/2005 - 02:34

Are you reading Gough?

1. For the state of P-t-MP traffic to change after 2-way is established, you have to actually change the network type on all routers to point-to-multipoint.

2. According to your link - section 8.1 of RFC 2328, OSPF sends a multicast packet for a point-to-point network-type even after the interface achieves the 2-way state.

3. The beef is that an interface can't form adjacency with more than one neighbor because it is an BRI/PRI/dialer interface (and hence, a point-to-point link). But you want the interface to act link a P-t-MP interface. So back to 1: change the network type on all routers to point-to-multipoint...

A circular argument, but then again, so is the problem! Would appreciate more thought on this,

Josef.

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Posted May 5, 2005 at 1:27 AM
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