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Re: Extreme Slowness
On Fri, 27 Oct 2006, [email protected] wrote:
Intermediate nodes are still discovered by "ICMP TTL Exceeded in transit" just like UDP based traceroute, ie the outgoing TCP SYN packet has a low TTL.For the record, TCP traceroute and similar TCP based tools rely on the fact that if you send a TCP SYN packet to a host it will respond with either a TCP RST (if the port is NOT listening) or a TCP SYN/ACK. The round trip time of this provides useful information which is unaffected by any ICMP chicanery on the part of routers or firewalls. A polite application such as TCP traceroute will reply to the SYN/ACK with an RST packet so it is reasonably safe to use this tool with live services.
So yes, tcptraceroute is good for getting thru firewalls in the forward direction, but intermediate routers are discovered in the same way by you getting an ICMP back because the TTL ran out.
Mikael Abrahamsson email: [email protected]