mahmoodmkl Thu, 07/02/2009 - 06:01


it enables forwarding of broadcast and multicast to the specified ip address.



Istvan_Rabai Thu, 07/02/2009 - 06:32

It is also important to know how it emulates broadcasts:

It sends a copy of the broadcast or multicast packet through each active Frame Relay PVC, thereby achieving a result similar to a broadcast network like Ethernet.



cisco@learn Thu, 07/02/2009 - 06:51


thanks for those info, if you could tell me about types of network in OSPF using Frame-Relay.



xcz504d1114 Thu, 07/02/2009 - 06:58

You can run any type of network in OSPF over frame relay, the broadcast key-word just allows the multicast (which is used by EIGRP and RIPv2 as well) that is destined to and (both of those are for OSPF depending on the network type).

Without the broadcast keyword you would have to use a neighbor statement, which converts the routing updates typically sent via multicast, to a unicast packet.

When you say "network" types, you could be referring to the OSPF network types stub networks, not so stubby areas, total stub area etc. Or you could be referring to broadcast networks, non-broadcast networks, non-broadcast multiaccess networks etc.

Either way, the broadcast keyword allows for neighbor adjacencies between routing protocols and routing updates. It is not always needed, and there are other ways to get the updates, such as using PPP over frame-relay.



cisco@learn Thu, 07/02/2009 - 08:26


I would like to know more about broadcast networks, non-broadcast networks, non-broadcast multiaccess networks etc. in OSPF. i am totally confused in those terms.



xcz504d1114 Thu, 07/02/2009 - 09:12

The short answer:

Broadcast Network - An example of a broadcast network is an ethernet network, a broadcast is a packet that is destined to all hosts, we typically use VLAN's to segment broadcast traffic. Routers use broadcasts for some routing protocols such as RIPv1.

In regards to frame-relay and OSPF in particular, broadcast also refers to multicast traffic. OSPF uses multicast as opposed to broadcasts to send routing information to other routers. Without the broadcast keyword, the routing updates would never be sent out a frame relay interface.

Non-broadcast Networks - An example of a non-broadcast network is frame-relay, in order to overcome this limitation that affects routing updates, you can either specify "broadcast" in the interface configuration of frame-relay, or specify a neighbor in the routing protocol:

router ospf 1


This would then send unicast routing updates instead of multicast routing updates.

Non-broadcast multi access Networks - Very similar to the frame-relay example, with the exception that it would use a virtual interface instead of a physical interface. To configure a virtual interface you could use something such as:

conf t

interface virtual-template 1

ip address

There really is a lot that is involoved with this subject.

Here is a link that discusses OSPF and multi-access networks:




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