Joe Abley (jabley) writes:
You drop the packet at your border before it is sent out to the Internet.
This is why numbering interfaces in the data path of non-internal traffic is a bad idea.
Unfortunately many providers have the bad habit of using RFC1918 for interconnect, on the basis that a) it saves IPs b) it makes the interconnect "not vulnerable" [1].
Packets which are strictly error/status reporting -- e.g. IMP 'unreachable', 'ttl exceeded', 'redirect', etc. -- should *NOT* be filtered at network boundaries _solely_ because of an RFC1918 source address.
I respectfully disagree.
Same here, and even if egress filtering didn't catch it, many inbound filters will. [1] I'v also heard of ISPs having an entire /16 of routable addresses for their interconnect, but they just don't advertise to peers.