Network setup help

[Matt Cooper]

Hey all --

This is probably a very basic thing and I'm just not doing it properly. I'm trying to connect two 1921 routers together using the following setup:

Router #1 

gi0/1 10.10.1.1 255.255.255.0

Router #2

gi0/1 10.10.7.1 255.255.255.0

There is currently a crossover connection in between the two (Confirmed working)

How do I make these two networks communicate with being on different subnets? I've tried several static routes, but I have not had any access.

Please assist me!

Thank you

[Richard Burts]

First I would like to understand why you are doing this? You are creating a situation where layer 2 says that these are locally connected devices and that they should be able to arp for each other and communicate directly. But your layer 3 setup says that they are remote connections and that arp should not work for each other and that they should have some gateway set up to facilitate communication.

My biggest concern about getting this to work is that a solution would require that the devices arp for each other's address. And the default behavior of IOS is that when it receives an arp request and the source address of the arp is not a local network that IOS rejects the arp request. If we were talking about connections through a switch there could be ways to get it to work. But I am not sure that routers connected in this way could work without something like a secondary address in the configuration.

HTH

Rick

[Matt Cooper]

Richard,

We are implementing an AT*T ASE Layer 2 point to point. We will have 4 total sites all connected through this system. We were trying to make each gi0/1 "WAN" interface its own subnet, for purposes of its easier to tell which site is which.

Example:

Router #2

WAN - 10.10.7.1

LAN - 192.168.7.1

We are trying to keep them in uniform I suppose you could say. Currently the reason for a crossover is its just a "lab" right now -- when its live, it runs on basically "access" ports on the AT&T side.

Please let me know if this makes sense.

[Richard Burts]

The explanation is helpful. Unfortunately what you are attempting to implement creates a conflict between what layer 2 believes to be true and what layer 3 believes to be true. Perhaps you can get some clarification from AT&T about how to deploy the ASE service. You describe it as point to point but most of what I have seen describes ASE in terms of Ethernet LAN which is multipoint.

If each of the sites will be using a 192.168 network then perhaps you might create a solution in which the ASE interfaces are configured to be in a common subnet and have the last octet of the ASE interface use the third octet of the site LAN. So if the site uses 192.168.7.0 this its ASE interface could be 10.10.7.7. And if another site uses 192.168.15.0 then its ASE interface might be 10.10.7.15.

HTH

Rick

[Matt Cooper]

Sorry, I should have said its "EVC" technology, point to point was not the correct way to describe it.

I've discussed with AT&T, they say all they do on their end is provide layer 2 connectivity and ports are set to access mode. That's typically all they can do.

I did not think this situation would work, but I wanted to attempt.

My setup was going to be each site was:

R1 - 10.10.1.1

R2 - 10.10.1.2

R3 - 10.10.1.3

R4 - 10.10.1.4

Do you see any issues with that? All remote sites will be pointing back to "10.10.1.1" as its the main site.

[Richard Burts]

Thanks for clarifying about the technology. If they just provide connection on a group of access ports then it becomes important that your implementation have the addresses in a common subnet (and in the same vlan if you were connecting switches instead of routers). I do not see any issues with the addressing that you are suggesting with 10.10.1.1, 10.10.1.2, 10.10.1.3, 10.10.1.4. Each remote site would need a router or layer 3 switch to provide connectivity and routing logic to forward traffic to the main site. The main site would need a router or a layer 3 switch to provide connectivity and routing logic to forward traffic to the appropriate remote site. This could be done with static routing or with some dynamic routing protocol.

HTH

Rick

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