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Frame Relay --CISCO

When configuring frame relay...
I have noticed  the encapsulation can be HDLC or PPP. Based on what element should someone make a pick.???

I also have noticed that configuring sub-interface, can be Point to point or Point to Multipoint. what is this based on ??

Thanks

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jskfan
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jskfan
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5 Solutions
 
adrianuta2004Commented:
when configuring FR you must setup encapsulation frame relay ( is a subset of hdlc )
(config-if)#encapsulation frame-relay ( phisycal interface command )

FR interfaces can be point-to-point, or point-to-multipoint, for example if you have branches: 1,2 and 3 and you only have a partial mesh topology(1-2,1-3), and you don't have a connection between 2-3, you can use point-to-multipoint, meaning that on 1 you configure dlci directly on phisycal interface, and you can create manually maping (dlci - ip address ). You can also use point-to-point between 1-3 and 1-2, meaning that you create subinterfaces on 1, and you assign manually a dlci address and ip  on each subinterface. When you use point-to-point: you have a different subnet on each point-to-point connection( so you waste ip addressess ), when you use point-to-multipoint you have same subnet ( but you have issues with routing protocols due to split horizon).
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SeeMeShakinMyHeadCommented:
agreed, you have to disable split horizon on the interface and specify the routing protocol in the command - unless you were using EIGRP stubs perhaps.
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mikebernhardtCommented:
Depending on your needs, you don't have to disable split horizon with point-to-multipoint. If the remote sites only have one path out to the hub, a much better way is to (assuming you're not using OSPF) use an outbound distribute list on the hub router which only permits the default route to go to the spoke routers. It's a good rule of thumb to not send out more routing information than is required to do the job. As long as the remote sites know that they have to go to the hub for connectivity to other remote sites, all will work well.

Even if you can't send the default route due to internet access coming from elsewhere on the remotes, you can still make it work if you're designed your ip addressing plan properly: All of the remote sites should be summarizable into aone or a few route entries, you can send those summaries to the remotes.

now, if you're building a full mesh the above won't work and you'll need to disable split horizon- but that's a lot more expensive and most people use a hub-and-spoke design for connecting multiple remote offices.
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jskfanAuthor Commented:
If I understand P2P or P2M is based on how many same/different subnets that the Hub has with spokes.

if a HUB has 2 or more spokes on the same subnets, then will go with P2M
if a HUB has 1 spoke in a certain subnet that is different from other Spokes' subnets, then will go for P2P.
Correct ????

what about the Choice between HDLC and PPP ? is is based on what?

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mikebernhardtCommented:
As someone posted before, the encapsulation has to be "frame-relay" if it's frame relay.
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SeeMeShakinMyHeadCommented:
Here is a pretty good article that explains it all.  

http://www.petri.co.il/csc_3_wan_protocols_you_should_know.htm
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jskfanAuthor Commented:
thank you guys!
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