Frame Relay problem

Answered Question
Oct 23rd, 2007

As i know Frame Relay networks are called NBMA(Nonbroadcasting multiaccess networks)CCNA ICND page 394.According to CCNP BSCI chapter 6 you can configure OSPF networks over Frame Relay as broadcasting or non-broadcasting. I am confused about this.

Thanks

moses

I have this problem too.
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Correct Answer by royalblues about 9 years 1 month ago

As described in RFC 2328, OSPF runs in one of the following two official modes in NBMA topologies:

1. nonbroadcast

2. point-to-multipoint

The nonbroadcast (NBMA) mode simulates the operation of OSPF in broadcast networks. Neighbors must be manually configured, and DR and BDR election is required. This configuration is typically used with fully meshed networks.

point-to-multipoint

The point-to-multipoint mode treats the nonbroadcast network as a collection of point-to-point links. In this environment, the routers automatically identify their neighboring routers but do not elect a DR and BDR. This configuration is typically used with partially meshed networks.

The choice between NBMA and point-to-multipoint modes determines the way the Hello protocol and flooding work over the nonbroadcast network. The main advantage of the point-to-multipoint mode is that it requires less manual configuration, and the main advantage of the nonbroadcast mode is that there is less overhead traffic.

So Point to multipoint option does not require neighbors to be manually defined as it is treated as a collection of P2P links.

It uses a single subnet to represent the network and uses multicast to discover the neighbors and does not require DR or BDR

Cisco has defined the following additional modes:

point-to-multipoint nonbroadcast

broadcast

point-to-point

HTH

Narayan

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royalblues Wed, 10/24/2007 - 00:27

Moses,

Frame relay networks are called as NBMA as they are multiaccess but do not have the capabilty of broadcasts as in case of LAN.

In reference to OSPF, the network type on the interface can be configured as either broadcast or Non broadcast.

If it is configured as broadcast, OSPF sends hellos and there is no need to manually define the neighbors

In case of Non Broadcast, the neigbors need to be defined manually as there is no broadcast/multicast capability for the hellos ot dynamically identify the neighbors

http://www.cisco.com/warp/public/104/22.html

HTH

Narayan

moses12315 Wed, 10/24/2007 - 01:31

Narayan thanks for your time. I just want to clear some things. I know three ways for destign a Frame Relay network.

1. Partial Mesh were all links are point to point. That's not a problem.

2. Full mesh were all Wan links are belong to the same network. As Frame Realy is a NBMA we have to assing the neighbors manually.

3. Hybrid approach were we have point to point links and point to multipoint links. About the point to multipoint since Frame Relay is a NBMA why we do not need to configure the neighbors manually.

Thanks

moses

Correct Answer
royalblues Wed, 10/24/2007 - 01:48

As described in RFC 2328, OSPF runs in one of the following two official modes in NBMA topologies:

1. nonbroadcast

2. point-to-multipoint

The nonbroadcast (NBMA) mode simulates the operation of OSPF in broadcast networks. Neighbors must be manually configured, and DR and BDR election is required. This configuration is typically used with fully meshed networks.

point-to-multipoint

The point-to-multipoint mode treats the nonbroadcast network as a collection of point-to-point links. In this environment, the routers automatically identify their neighboring routers but do not elect a DR and BDR. This configuration is typically used with partially meshed networks.

The choice between NBMA and point-to-multipoint modes determines the way the Hello protocol and flooding work over the nonbroadcast network. The main advantage of the point-to-multipoint mode is that it requires less manual configuration, and the main advantage of the nonbroadcast mode is that there is less overhead traffic.

So Point to multipoint option does not require neighbors to be manually defined as it is treated as a collection of P2P links.

It uses a single subnet to represent the network and uses multicast to discover the neighbors and does not require DR or BDR

Cisco has defined the following additional modes:

point-to-multipoint nonbroadcast

broadcast

point-to-point

HTH

Narayan

please rate all useful posts

moses12315 Wed, 10/24/2007 - 01:39

Narayan thanks for your time. I just want to clear some things. I know three ways for destign a Frame Relay network.

1. Partial Mesh were all links are point to point. That's not a problem.

2. Full mesh were all Wan links are belong to the same network. As Frame Realy is a NBMA we have to assing the neighbors manually.

3. Hybrid approach were we have point to point links and point to multipoint links. About the point to multipoint since Frame Relay is a NBMA why we do not need to configure the neighbors manually.

Thanks

moses

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