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

[Joe Maimon]

Spencer Barnes wrote:
> Hello,

> 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.

Only with proxy-arp.

Your provider has put that subnet on the wire. Seems like they want to 
add 60 more macs to their devices mac tables.

Go explain to them, route where you can bridge where you must.

And get at minimum a /29 for a barrier/transit segment, aside from the 
range you will route/nat/loopback how you see fit. Public routed is best 
for you, but either will work for this purpose.

>
> Is there a better way to do this so I can use all the IPs in the range?

So you would be breaking it down like this

/30 on external interface
/30 for loopbacks on the router
/29 secondary internal subnet, loses 3 addresses
/28 secondary internal subnet, loses 3 addresses
/27 secondary internal subnet, loses 3 addresses

network takes 17, other devices = 47

that compares to /26 bridged/static-nat

gateway, network, broadcast, your gateway = -4, other devices = 60

With a difference of a dozen available addresses so critical to you, I 
doubt a /26 provides you with what you need anyways.

Sounds like you are currently multi-homed, apply to either ISP for a /24 
for BGP or directly to ARIN.

Or bridge and nat. Or use vrf's, or multiple routes with static routes 
and nats and (again) proxy arp.


Joe