[FW1] Off-topic (somewhat): How does traceroute work, anyway?

["Reed Mohn, Anders" <Anders.Reed.Mohn@FW1-NOSPAMitcompagniet.no>]

I've just upgraded to CP2000, and I since I was at it, I used the
opportunity to
clean up my rulebase a little.
I threw out all the implied rules and set what was needed back up
"manually".

I thought I'd seen the answer to this on the list once, but I haven't been 
able to find it in the archives.
Here's the question:

In adding rules to allow ping / traceroute, I added a rule to allow incoming

ICMP dest-unreachable, echo-reply and time-exceeded.

Now why a time-exceeded message? This goes to how traceroute
works, I suppose.
I'm guessing that traceroute sends out packets with an increasing TTL,
until an echo-reply from the destination comes back. Is this correct?

Cheers,
Anders RM :)


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