EIGRP over NBMA Network

[riyaaz000]

Hi everyone,

Just for information, am preparing for the CCNP ROUTE Exam. I like to dig deeper on things thats not clear to me.

Currently am reading on EIGRP over NBMA network (precisley frame-relay) and cannot understand the concept of "broadcast" statement at the end of "frame-relay map ip address dlci number broadcast" command line. As far as my understanding is, is that its like EIGRP package the EIGRP Multicast address in a unicast address. Is that feasible or I wrongly understand the concept.

Can anyone help me out here.

Regards

Riyaaz

[Inderjeet Singh · Accepted solution]

Hi,

EIGRP uses multicast address to discover neighbor and send updates.. but as frame-relay is non-broadcast medium, you have to specifby the 'broadcast' keyword with frame-relay map ip address command so that multicast updates can travel through non-broadcast medium..

Thanks

Inder

[riyaaz000]

Hi Inder,

Thanks for the reply.

Assume router A is about to send hellos to router B and vice versa, does the broadcast keyword modify the source/destination address in the IP header??

Regards

[Bilal Nawaz · Accepted solution]

The broadcast keyword will allow for the routers to send to 224.0.0.10 just like on an ethernet segment. Doesn't modify the packets to my understanding.

http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml

The Keyword broadcast

The broadcast keyword provides two functions: it forwards broadcasts when multicasting is not enabled, and it simplifies the configuration of Open Shortest Path First (OSPF) for non-broadcast networks that use Frame Relay.

The broadcast keyword might also be required for some routing protocols -- for example, AppleTalk -- that depend on regular routing table updates, especially when the router at the remote end is waiting for a routing update packet to arrive before adding the route.

By requiring selection of a designated router, OSPF treats a non-broadcast, multi-access network such as Frame Relay in much the same way as it treats a broadcast network. In previous releases, this required manual assignment in the OSPF configuration using the neighbor interface router command. When the frame-relay map command is included in the configuration with the broadcast keyword, and the ip ospf network command (with the broadcast keyword) is configured, there is no need to configure any neighbors manually. OSPF now automatically runs over the Frame Relay network as a broadcast network. (See the ip ospf network interface command for more detail.)

Likewise very similar to EIGRP.

Hope this helps.

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[riyaaz000]

Thanks Bilal,