Trace Route Operation

eng_ahmedas

Dear Friends
I wish u r all in very good health.I confused a little about trace route and wish u could help me in it.

In trace route operation (as i understand), it sends 3 udp packets to invalid port (33434) with incremental TTL until the destination replay with port unreachable. But in the extended traceroute , you can change the port number (i use port 80 as example) and it will work ok ... how come ??? Is the operation of trace route really depends on this invalid port or not??? and if it doesn't depends on this port, how the trace route operation done successfully....

I wish u could help me

Thanks in advance

sprkymrk

eng_ahmedas wrote:

In trace route operation (as i understand), it sends 3 udp packets to invalid port (33434) with incremental TTL until the destination replay with port unreachable. But in the extended traceroute , you can change the port number (i use port 80 as example) and it will work ok ... how come ??? Is the operation of trace route really depends on this invalid port or not??? and if it doesn't depends on this port, how the trace route operation done successfully....

Here is a very good link:

http://www.cisco.com/warp/public/105/traceroute.shtml

The destination port is also incremented (33434, 33435, 33436) BTW.

Check out the debug outputs in the example, and also the summary at the bottom of the link. Remember you're not looking for an open port, you're just looking for the path the packets are taking to reach the destination. So you just want to know each router in the path along the way, and when you send a packet through them (not to them) but the router sees that the TTL is exceeded, it sends a response back to you. So the port itself doesn't matter much.