Why is Frame Relay Non Broadcast
up2thetime
Member Posts: 154
in CCNA & CCENT
Just curious as to why FR is considered NBMA.
If I add the broadcast keyword to my frame relay maps, I have broadcast capability.
If I let Inverse ARP do it, broadcast capability also exists by default (broadcast is in the output of show frame-relay map).
When using all the defaults in a multipoint set-up, inverse arp allows broadcasts.
The only way that a multi-point set-up wouldn't support broadcasts is if inverse-arp is manually disabled, and then the broadcast keyword is left out of the map statements. However this is not the default behaviour.
So why call it non-broadcast?
If I add the broadcast keyword to my frame relay maps, I have broadcast capability.
If I let Inverse ARP do it, broadcast capability also exists by default (broadcast is in the output of show frame-relay map).
When using all the defaults in a multipoint set-up, inverse arp allows broadcasts.
The only way that a multi-point set-up wouldn't support broadcasts is if inverse-arp is manually disabled, and then the broadcast keyword is left out of the map statements. However this is not the default behaviour.
So why call it non-broadcast?
Comments
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MickQ
Member Posts: 628 ■■■■□□□□□□
Because it is a non broadcast medium.
The only reason why you have the "broadcast capability" is because that actually tricks the router into taking the broadcast it receives from your ethernet (broadcast) medium, and sends a unicast of that frame out to each mapped dlci. -
NetworkVeteran
Member Posts: 2,338 ■■■■■■■■□□
up2thetime, set up a hub and spoke frame-relay topology: a <===> b <===> c. Now, use all the broadcast keywords you want. Configure OSPF. See whether a and c are neighbors. Do a "debug ip ospf hello". See if a and c see each other's hello's (although to be technical those are multicasted, not broadcasted).
Because spoke devices cannot see many multicasts / broadcasts, it's standard practice when using OSPF on hub and spoke frame-relay networks to set the spoke routers' priorities low so they can never become DRs.