FR Point-to-Multipoint & Non-Broadcast MultiAccess

Unanswered Question
Feb 14th, 2008

Hi Pros,

I would like to know in Frame Relay Terminology, Point to Multipoint configuration and Non-Broadcast Multiaccess are meaning the same techniques.

thanks in advance..

I have this problem too.
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aravindhs Thu, 02/14/2008 - 08:07


Non Broadcast Multiaccess -

NonBroadcast means that it is unlike Ethernet where a broadcast is heard by everyone on the segment. FRelay uses Virtual Circuits for eg. like a one-to-one communication over a telephone circuit ..

You might know about creating multipoint and point to point subinterfaces on the IOS based routers. When you configure frame-relay encapsulation on such a sub-interface, you could have multiple virtual circuits on one layer 3 IP subnet. This would mean, each broadcast message will have to be replicated to each PVC on the multipoint sub-interface to make it emulate a multi-access segment - like frame-relay. Compare it to a three way conference over a telephone where voice from your line is replicated to both the listeners on different lines.

Hope this makes sense.



Mohamed Sobair Thu, 02/14/2008 - 17:08


Frame-relay is a NBMA (NON Broadcast Multiaccess)media. NBMA is a media that doesnt support (ARP/Broadcast) unlike Ethernet media.

As for Point to Multipoint, its Framerelay (Hub & Spoke) terminology, like having a head office has multiple branches.



shivlu jain Thu, 02/14/2008 - 21:40

hi arun

point to multipoint is used at that time when you will be having all the ips in the same subnet.

NBMA is a technology which is used in the ospf by default all the serial interfaces in the ospf published in the nBMA mode you can check with sh ip ospf interface serial

so if you want to make the neighbor ship in two then you have to use the old method that is by adding a command called neighbor or you can use the keyword broadcast.



Mohamed Sobair Fri, 02/15/2008 - 13:16

Hi arun,

I think your concern was a bout Frma-relay (NBMA) & Point to multipoint terminology more than how a specific routing protocol works over it.

Pls let me know if you need to know how a routing protocol behaves over NBMA.

(Specificly OSPF, cause it has special Characteristics here).




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