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

[Chuck Church]

Yeah, that's the way we used to do it.  Does make troubleshooting a little
more difficult.  /30 is best.   Or if they're super-stingy, /31.

Chuck

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Tom Storey
Sent: Tuesday, July 10, 2012 5:04 AM
To: Spencer Barnes
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Overlapping Subnet Issue - Gateway IP Resides in Vendor
Assigned Public IP Range

Could you do something like this (writing from memory, so forgive me if this
is wrong):

interface LAN
 ip address 10.0.128.66/26
!
interface T3
 ip unnumbered LAN
!
ip route 0.0.0.0 0.0.0.0 10.0.128.65 (or maybe specify the T3 interface
instead of IP next hop) !

Something similar used to work for PPP ADSL connections, maybe it could work
here too?

But I would tend to agree with most people here, ask them to assign you a
point to point subnet (heck even a /31 if they are concerned about IP usage)
and route the /26 to you.

On 9 July 2012 23:13, Spencer Barnes <spencer at ceiva.com> wrote:
> Hello,
>
> I'm trying to move to a new ISP.  Our old one provided a T3 and an
external IP range.  The gateway IP they gave to us to assign to our router
interface was on a different subnet than the external IPs they provided so
having another interface dedicated to the external network was an easy
setup.
>
> 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.
>
> Is there a better way to do this so I can use all the IPs in the range?
>
> Thanks in advance for any input.
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