Breaking up the supernet at each end.

[digiandy]

Hello all,

I am a little stumped here and have been reading for an answer all night with no luck, so I thought I would post.

We moved to a new MPLS network with our provider. We have 4 subnets at each location. All /24 bit masks.

LOCATION A, 10.128.0.0,10.128.1.0, 10.128.2.0, 10.128.3.0
LOCATION B, 10.128.4.0,10.128.5.0, 10.128.6.0, 10.128.7.0
etc....

So our isp just routed the supernets to each location on the mpls network.
LOCATION A, 10.128.0.0/22
LOCATION B, 10.128.4.0/22
etc...

my question is, how do i break them back apart? I have cisco 3725s with 5 FE interfaces at each location. (We are also using ASA5510 for the internet that comes on a different port from our isp, but this is a different topic.)

I know I can assign each subnet to 4 of the FE interfaces, but the transport interface (interface connected to port provided by isp) is where i get confused. do i just assign that an IP address with a 22bit mask (i.e. 10.128.0.2/22) or will it get confused and think its on the same subnet as the other interfaces? i have considered EIGRP, etc, but I don't know if my isp is running any of those protocols and am concerned about the other interfaces being part of the same supernet.

Any help would be appreciated.

Thanks

Andy.

 

[jneiberger]

Your provider should have given you IP addressing for the ISP link. Just assign the /24s to your local interfaces and all will be well.

 

[digiandy]

jneiberger, thanks for the response.

The port on the providers router has an address of 10.128.0.1 so it is a local address. So I am still worried about a conflict of interface addresses, but I could be wrong.

Can I apply 10.128.0.2/22 to an interface on my router as well as the 4 corresponding /24 networks to each of the other interfaces?

Thanks

 

[jneiberger]

There's no need to assign the entire /22 to any interface. The ISP has a /22 route pointing to your router. Once a packet arrives at your router, the router will route that packet to the appropriate /24.

 

[digiandy]

So do i plug the router from the isp into a port on my router with no ip assigned and use all 5 ports? or do i plug it in to the 1st subnet port and just use 4 ports total?

sorry if i am sounding stupid right now. I really appreciate your help.

 

[jneiberger]

All five interfaces need to be routed interfaces, not switched. Configure the ISP interface with the IP addressing they gave you. Configure the /24s on the other interfaces. That's it!

Well, you need to configure a default route pointing back out toward your ISP, but that's a separate issue from your question.

 

[digiandy]

jneiberger,

I will do this tonite when i get back over there. Thanks so much for your help.