North American Network Operators Group
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Re: Alternate and/or hidden infrastructure addresses (BGP/TCP RST/SYNvulnerability)

  • From: sthaug
  • Date: Fri Apr 23 10:38:52 2004 
> > (TTL should only be decremented when _forwarding_, and I don't think
> > you could argue that you need to _forward_ a packet from your ingress
> > interface to your _loopback_ interface..)
> 
> Well, if that were the case, then you wouldn't need multi-hop to do 
> loopback peering.

Different issue (directly connected interfaces vs not directly
connected).

Easy test: Connect two routers (I used Ciscos) to the same Ethernet
switch, sniff the traffic between them. Ping from one router to the
other on the directly connected interfaces, observe TTL with sniffer.
Ping from loopback on one router to loopback on the other, observe TTL
again. I see the *same* TTL in both cases, which means that at least
for the IOS version I was testing, TTL is not decremented when sending
from the loopback interface.

Steinar Haug, Nethelp consulting, [email protected]