[clug] Re: Determining availability of a remote machine

Jepri jepri at webone.com.au
Wed Apr 2 17:47:30 EST 2003

On 2003.04.02 17:43, Steve Jenkin wrote:
> 'traceroute' relies on the proper intermediate handling of expired
> 'time to
> live', not ICMP ECHO (ping).
> >From my (linux) manpage:
>         -I     Use ICMP ECHO instead of UDP datagrams.
>        -p     Set  the  base  UDP  port  number  used  in  probes
>               (default is 33434).  Traceroute hopes that  nothing
>               is  listening on UDP ports base to base + nhops - 1
>               at the destination host (so an  ICMP  PORT_UNREACH­
>               ABLE  message  will  be  returned  to terminate the
>               route tracing).  If something  is  listening  on  a
>               port  in the default range, this option can be used
>               to pick an unused port range
> ... .then listening for an  ICMP  "time  exceeded" reply from a
> gateway.
> --
> Would be nice if it would use an designated TCP port, would work just
> as well
> and could be 'jiggled' to go through various firewalls. [tcp:80/http
> is an
> obvious default choice]

This is already part of the ping standard.  Try looking in your 
/etc/services file.  It's almost always commented out.

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