[c-nsp] Overlapping Subnet Issue - Gateway IP Resides in Vendor Assigned Public IP Range

[Spencer Barnes]

I'm trying to avoid NAT.  

Could I assign say 10.0.128.69 255.255.255.252 to g0/1, then do several static routes?

g0/0 (WAN)
ip add 10.0.128.66 255.255.255.252
g0/1 (Public LAN)
ip add 10.0.128.69 255.255.255.252

Ip route 0.0.0.0 0.0.0.0 10.0.128.65
ip route 10.0.128.68 255.255.255.252 GigabitEthernet0/1
ip route 10.0.128.72 255.255.255.252 GigabitEthernet0/1
ip route 10.0.128.76 ...
ip route 10.0.128.80 ...

And so on until I hit 10.0.128.96 where I can make it a /27?

All the devices behind the g0/1 interface would be placed in the 10.0.128.64/26 network with a default gateway of 10.0.128.69.  

Not pretty but everything should still route OK in this setup?



-----Original Message-----
From: sp-privat at locus.tech.iphh.net [mailto:sp-privat at locus.tech.iphh.net] On Behalf Of Sascha Pollok
Sent: Monday, July 09, 2012 5:03 PM
To: Chris Evans
Cc: cisco-nsp at puck.nether.net; Spencer Barnes
Subject: Re: [c-nsp] Overlapping Subnet Issue - Gateway IP Resides in Vendor Assigned Public IP Range

Spencer,

> You could have your isp assign a transit ip subnet for the link and 
> then out your ips internal your border router. Another thing you could 
> do static nats if the first option isn't available.
> On Jul 9, 2012 7:50 PM, "Spencer Barnes" <spencer at ceiva.com> wrote:
>
>> Hello,
>>
[...]
>> Our new ISP provided a gateway IP that is in the same subnet as the 
>> external IPs they provided for use.  The range they provided (changed 
>> for
>> security) is 10.0.128.64/26.  They want us to assign 10.0.128.66 to 
>> our WAN interface and point all outbound traffic to 10.0.128.65.
>>
>> The problem with this setup is I can't dedicate another interface for 
>> the new external range because the subnets overlap.  I can change the 
>> g0/0 interface to 10.0.128.66 255.255.255.252 and assign the other 
>> interface
>> g0/1 10.0.128.96 255.255.255.224 but then I lose a bunch of external IPs.

As Chris has said. When you got a T3 or similar we are not talking about some cheap residential thing. You ISP should provide a transit network!

-Sascha