[arin-ppml] ARIN-prop-127: Shared Transition Space for IPv4 Address Extension

[Jack Bates]

On 1/20/2011 4:28 PM, George, Wes E [NTK] wrote:
> 1) ISP assigns the same block of 1918 space to the external interface as is
> already in use on the internal interface of a customer's home GW router and
> badness ensues.

For many years (the last isolated network was finally cleaned up 2 years 
ago), different sections of the telco networks I manage used RFC-1918 
and PAT. The last one was a 300+ subscriber wifi service, which 
renumbered into real IPs when they changed out wireless hardware on the 
towers a few years ago.

Reasons the PAT went away were standard troubleshooting/tracking issues, 
as well as load on the routers (they were low end software based 
routers). Largest complaint was breakage of VPN/ipsec software which 
wouldn't (or they didn't know how to make it) do NAT-T. In one case, NAT 
went away as I upgraded the router to a code which wouldn't support NAT. ;)

For the record, we almost exclusively used 10.0.0.0/20 or longer in 
these environments. Problems with customer router conflicts was the 
smallest of problems introduced by using NAT.

Jack