From: Danny McPherson <danny@genuity.net> Subject: Re: simple question as always.. Date: Mon, 09 Mar 1998 18:33:56 -0700 Message-ID: <199803100133.BAA06340@ice.genuity.net> Hi, tatsuya> could someone explain to me why I can ping but traceroute tatsuya> seems to have problem reaching it.
The combination of a firewall (permitting ICMP echo replies/requests, but filtering your UDP traceroute probes) .. and a traceroute client that doesn't correctly handle (IMO) the response (ICMP Type 3, Code 13: Communication Administratively Prohibited).
tracert with WindowsNT4.0 uses ICMP ECHO messages for probing packets. Hence one might go through the filtering router boxes. :) tatsuya> I was told once that traceroute required each router on the tatsuya> way to KNOW something whereas ping does not. tatsuya> I just can not recall what this something is and I am tatsuya> intend to find out. traceroute ends its probing when it receives a ICMP port unreachable message. Filtered by an IP gateway like cisco boxes, it receives Communication Administratively Prohibited messages and continues probing by incrementing IP TTL. ------- Toshio Shigematsu