Jonathan Chen presented these words - circa 3/10/08 7:38
PM->
> On Mon, Mar 10, 2008 at 11:30:05PM +0100, Wojciech
Puchar wrote:
>
> [...]
>> traceroute uses UDP packets, no special port
numbers.
>
> traceroute(8) indicates that the default UDP port
number used is
> udp/33434, incrementing for each hop out.
The incrementing is the TTL count in the IP header, not the
port number.
It works by sending out a UDP packet for a (generally)
unused port with
the TTL field to a specific number and looking for ICMP
errors to
indicate how far the packet went (the last node address is
contained in
the ICMP error reply). However, be warned, some network
administrators
disable their routers from sending back these types of ICMP
messages
to prevent you from learning about their routing paths. In
these cases,
you get back the "1 * * *" type of output from
traceroute. Also, by
default traceroute attempts to do a reverse DNS on the IP
address, so
you can speed things up by doing a 'traceroute -n' to avoid
this look-up.
Patrick
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