Subject: Re: Clarification on Cisco OSPF network types

From: Paresh Khatri <[email-masked]>
Date: Wed, 25 Jun 2003 11:56:06 +1000

Thanks you Sina,

This has been very useful.

Regards,
Paresh.

>>> [email-masked] 06/25/03 11:15AM >>>
Paresh,

->Hi all,
->
->Appreciate if someone could clarify how the various Cisco
->OSPF modes for NBMA networks work.
->
->The command "ip ospf network {broadcast | non-broadcast |
->{point-to-multipoint [non-broadcast] | point-to-point}}"
->allows you to set an OSPF network mode.
->
->I would like to know:
->1.  How OSPF packets are transmitted on each of these modes -
->unicast, multicast etc ?

network \packet type |type 1 | type 2| type 3| type 4| type 5
---------------------|-------|-------|-------|-------|------
p2p                  |  M    |   M   |   M   |   M   |  M
---------------------|-------|-------|-------|-------|------
p2mp non-broadcast   |  U    |   U   |   U   |   U   |  U
---------------------|-------|-------|-------|-------|------
p2mp broadcast       |  M    |   U   |   U   |   U   |  U
---------------------|-------|-------|-------|-------|------
NBMA                 |  U    |   U   |   U   |   U   |  U
---------------------|-------|-------|-------|-------|------
Broadcast            |  M    |   U   |   U   |M /MD *|  M/MD *

U  : unicast ( neighbor IP address )
M  : Multicast AllSPFRouters (224.0.0.5)
MD : Multicast AllDRouters ( 224.0.0.4 )

* For broadcast network, if Interface FSM is DR /BDR type 4 & 5 are sent
to M ( 224.0.0.5) otherwise it is sent to MD ( 224.0.0.4 )

->2.  How are neighbors discovered ?

When the packet ( actually Hello ) is sent to unicast IP address a
manual configuration is required (except for VL which is found
dynamically once there is an intra-area path to the other end-point )

If Hello is sent to Multicast AllSPFRouters address and the link layer
has the broadcast capability ( or packet can be replicated to sent to
different VC ) then the neighbor discovery is dynamic

Sina

->
->All responses appreciated.
->
->Regards,
->Paresh.
->