Re: Strange Network Problem (TTL?)

[Fraser Campbell <fraser@baxter.net>]

Chris Wagner wrote:

> So it's really a max hops limit.  How did it get a name like TTL??  What
> function does it serve?  Besides providing a mechanism to expire lost
> packets...  What role does each host's TTL setting play in a ping or trace?

When you receive a ping reponse the TTL is determined by the remote
computer's TTL setting.  If that computer's default TTL is 64 and you are
20 hops away you will see a TTL of 44 on the ping responses.

Win95/NT3.51 both had a default TTL of 32 which is definitely not
sufficient for today's Internet.  Those computers will find a lot of their
packets not reaching destinations.  There's quite a lot of documentation
about this on the Internet, here are a couple of URLs:

http://www.switch.ch/docs/ttl_info.html
http://cne.gsfc.nasa.gov/tcpipsvcs/netwkutil/traceroutetutorial.html

Linux 2.0.x appears to have a default TTL setting of 64.  Linux 2.2.x
appears to have a default TTL setting of 255. Win98/NT4 have a default TTL
setting of 128 IIRC.  I don't remember Win2k's setting right now.  I would
assume the Linux default TTL is tunable via /proc but perhaps not, Windows
is tunable via the registry.

Fraser