OSPF Network types

carl_townshend · ‎10-09-2008

Hi all, when we talk about ospf networks

I believe there are a few types, ie broadcast/p2p , multipoint, NBMA etc

are there are any more ?

and what does it mean ?

Calin C. · ‎10-09-2008

Hello!

OSPF classifies different media into the following three types of networks by default:

Broadcast networks (Ethernet, Token Ring, FDDI)

Nonbroadcast multiaccess networks (SMDS, Frame Relay, X.25)

Point-to-point networks (HDLC, PPP)

Point-to-multipoint networks (Frame Relay)

If you want more explanation I can recommend reading: http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

and

http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cospf.html

Good luck!

Calin

Marwan ALshawi · ‎10-09-2008

OSPF defines various 'network

types'. These network types are:

Broadcast

Non-Broadcast

Point-to-Point

Point-to-Multipoint

Point-to-Multipoint Non-Broadcast

Loopback

The default OSPF network type on multipoint Frame-Relay interfaces is nonbroadcast.

In order to establish adjacency on an OSPF non-broadcast network

segment OSPF hello packets must be sent as unicast packets. This is

accomplished by issuing the neighbor statement under the OSPF process

if helpful Rate

tcordier · ‎10-09-2008

The NW types in OSFP define how the OSPF peer routers build their relationships (adjacencies) and how the individual OSPF routers build up their database with routing information.

The main differences are a) is the adjacency automatic (and you do not need to configure a neighbor statically) and b) will the OSPF peer routers elect a DR (Designated Router), or not?

Regarding the 5 main network types (see the 2nd post) you have:

"Non-broadcast" network types (inc. P2MP non-BC) do not build automatic adjacencies, and you need the neighbor statement.

"Point-to-Point/Multipoint" network types do not elect a DR. The others do, and you must be careful which router is elected DR.

The network type an interface uses once you have configured OSPF can be checked with sh ip ospf interface.

For more information, check the OSPF Design Guide (the first link in the first post, a excellent source of information on OSPF).

HTH, Thomas