Re: Strange public traceroutes return private RFC1918 addresses

[Bob Snyder <rsnyder () toontown erial nj us>]

Matthew Crocker wrote:

> Search the archives,  Comcast and other cable/DSL providers use the 
> 10/8 for their infrastructure.  The Internet itself doesn't need to be 
> Internet routable.  Only the edges need to be routable. It is common 
> practice to use RFC1918 address space inside the network. Companies 
> like Sprint and Verio use 'real' IPs but don't announce them to their 
> peers on customer edge routes.

Which (as discussed previously) breaks things like Path MTU Discovery, 
traceroute, and other things that depend on the router sending back ICMP 
packets to the sender if any ISP along the return path (properly) 
filters RFC1918 address space as being bogus. You can use RFC1918 space 
on any device that really has no need to communicate with the outside 
world, but generally, un-NAT'ed routers don't qualify for this, at least 
on their transit interfaces.

I believe Comcast (and I'm going only on my experience as a customer) is 
or has moved from RFC1918 space to routable IP space for their routers, 
at least on interfaces I've been doing traceroutes through.

Bob