From: Ananth Vk (ananth.vk@tcs.com)
Date: Wed Nov 14 2007 - 06:49:49 ART
Hi Everyone,
Good Morning !
Was going thru ospf nwk types in Jeff Doyle, cisco site & netcraftsmen &
have a few clarifications..
ok, My understanding of network types...There are 5 of them
1. Point to Point (Serial / PPP/HDLC)
2. Broadcast (Ethernet, Token ring)
3. Point to Multipoint Nonbroadcast-NBMA- (FR, ATM) (partial mesh,
neighbour cnds need to be added)
4. Point to Multipoint Broadcast (FR, ATM), (For full mesh, no neighbor
setup needed)
5. Virtual Links (B/w two ABRs to connect partitioned area / to connect an
area that dont have direct area 0 connectivity)
My understanding, pls correct if im wrong
1. Is DR election mandatory for all the 5 network types ? only for 2,3,4 i
guess.
2. OSPF updates are sent in the form of unicast for 1 & 5, broadcast for
2,4 and multicast (only when selective routers need to recv updates) for 3
3. Neighbour command is mandatory only for 3
4. FR if im right will fit with 3 (partial mesh) & 2,4 (full mesh)....can
any other type be used with FR ?
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From http://www.cisco.com/en/US/docs/ios/11_3/feature/guide/ospfpmp.html
OSPF has two new features related to point-to-multipoint networks. One
feature applies to broadcast networks; the other feature applies to
nonbroadcast networks.
?On point-to-multipoint, broadcast networks, there is no need to specify
neighbors. However, you can specify neighbors with the neighbor command,
in which case you should specify a cost to that neighbor.
?On point to multipoint, nonbroadcast networks, you now use the neighbor
command to identify neighbors. Assigning a cost to a neighbor is optional.
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From http://www.netcraftsmen.net/welcher/papers/ospf3.htm
You can configure an interface as any type you wish.
Broadcast is typically used on networks where broadcast and multicast are
supported. The idea is to send out one OSPF multicast that reaches
multiple receivers. This can be appropriate with X.25 and Frame Relay if
you have a full mesh of PVC's. Loss of a PVC can cause problems with OSPF
broadcast networks, however, since some routers with a common subnet will
no longer be able to transmit directly to each other.
Non-broadcast is used where broadcast/multicast is not feasible. The
drawback to this interface type is that neighbors must be explicitly
configured,
which can get to be a nuisance.
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Thanks
Ananth
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