On Sat, 7 May 2005, William Chops Westfield wrote:

>> the specific part of icmp that allows traceroute to work is ping/echo
>
> No.  By default traceroute uses a UDP datagram.  It's sent with a 
> time-to-live of one hop, and the router that discards it because of 
> TTL expired sends back an ICMP "time exceeded" message.  Then it sends

... absolutely correct but there are practically no routers programmed 
to block UDP so if there is something that fouls traceroute then it is 
usually the blocked ICMP protocol, which is usually marked as 
'ping/echo' in consumer router setup menus.

Also the * * * output from traceroute is caused by routers and hosts not 
retunrning ICMP time exceeded messages as you said.

Peter
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