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

[Sascha Pollok]

Don't do that to make your supplier's life easier. Ask them to assign
a transit-network and forget about complicated setups like this - really.
It saves you a lot of headaches (probably).

Cheers
Sascha

On Tue, 10 Jul 2012, Spencer Barnes wrote:

> 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
>
>