remote sites with EIRGP

[Timothy Burns]

I have just a basic EIGRP question.

We are using EIGRP with layer 3 swiches on the edge. Up until now for our interfaces I was just cutting up a /24 bit subnet into individual subnets for each link.

For example

172.16.1.0 255.255.255.252 - subnet

172.16.1.1(interface on core)

172.16.1.2(interface on layer 3 switch)

We are getting ready to move to ATT for our metro E sites using their point to multi point technology, meaning we have one connection to ATT's network and is how we connect to the remote sites which also connect back to ATT.

Since I will not be able to have a single interface on the core for each site, I was thinking of using a subnet such as

172.16.3.0 255.255.255.224 subnet

172.16.3.1 (core interface)

172.16.3.2(remote site interface

172.16.3.3(remote site interface)

and so on

Do you foresee any issues with this?

[Peter Paluch]

Hi Tim,

Assuming ATT is going to provide with some sort of Ethernet-like service (where all sites "sit" on the same segment and all unknown unicasts/multicasts/broadcasts are delivered to all sites) then your idea of having a common backbone network is perfectly fine. With regard to pure addressing, there should be no problem. It would perhaps be useful to find out as much info as possible about how does the ATT service behave from the customer's point of view.

Best regards,

Peter

[John Blakley]

Along with what Peter said, is this MPLS or is it a true point-to-multipoint where your location becomes the hub? If it's the latter, you could run into split horizon issues with eigrp where sites that are advertising to your hub and your hub won't readvertise those same subnets back out. You can disable this on the interface to allow routes to go out if needed.

If it's MPLS, you shouldn't have these issues because you'll actually peer with the provider's PE router.

[Timothy Burns]

Thanks for the replies and info.

j.blakley - As far if it is a true point to multipoint or not, I am not certain of the difference. But it is using layer 2 links and forwarding traffic to their persective sites based on mac address tables. There are a few other particulars with it but that is the basic extent of it and how it was explained.

Thanks again