<< | Thread Index | >> ]    [ << | Date Index | >> ]

Subject: TTL values?
From: "R. Steve McKown" <rsmckown,AT,yahoo,DOT,com>
Date: Thu, 22 Mar 2001 04:28:12 +0100

I've got a CIPE 1.5.1 tunnel running between two destinations on the 
internet.  Looking at traceroute and tcpdump output, I'm certain that 
the ttl value of the ICMP packet being sent over the tunnel is used as 
the ttl value for the udp packet which encapsulates it.

My two machines are 7 hops apart.  Doing a traceroute from one to the 
other should generate 1 line of output (as least in my mind).  However, 
seven lines are generated:

[root@router /root]# traceroute 10.0.0.1
traceroute to 10.0.0.1 (10.0.0.1), 30 hops max, 38 byte packets
1  * * *
2  * * *
3  * * *
4  * * *
5  * * *
6  * * *
7  10.0.0.1 (10.0.0.1)  74.008 ms  201.982 ms  55.951 ms

Also, if looking at tcpdump, the first udp packet out after traceroute 
starts has a ttl value of 1.

This behavior seems wrong, in that the underlying network which carries 
the tunnel traffic is more or less invisible to the software that uses 
the network path provided by the tunnel.  Is this a defect, or am I 
missing something in my reasoning?

Thx for the help
Steve





<< | Thread Index | >> ]    [ << | Date Index | >> ]