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Community Member

Broadcast in FrameRelay network

"Frame relay networks are considered to be Non-Broadcast Multi-Access (NBMA) networks", Is this mean Frame Relay cannot do broadcast at all? I know that I can add the broadcast parameter to the command ("Router(config-if)#frame-relay map") to configure the router to forward broadcast traffic over the link. If it can do broadcast why it is call NBMA? What if I don't want to use manual mapping but Inverse ARP ("Router(config-subif)#frame-relay interface-dlci")? Can I still make broadcast work in that case? What about multicast? Can Frame-Relay do multicast?

Community Member

Re: Broadcast in FrameRelay network

Frame Relay can send copies of a L3 broadcast over all VCs, but there is no equivalent to LAN broadcasts. In other words, no capability exists for a Frame Relay DTE to send a single frame into the Frame Relay network and have that frame replicated and delivered across multiple VCs to multiple destinations. However, routers need to send broadcasts for several features to work. In particular, routing protocol updates are often broadcasts.

Cisco IOS software sends copies of the broadcasts across each VC, assuming that you have configured the router to forward these necessary broadcasts.

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.

Note: The OSPF broadcast mechanism assumes that IP class D addresses are never used for regular traffic over Frame Relay.


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