[Asterisk-Users] Re: How is Teliax ?

[Kristian Kielhofner]

asterisk at anime.net wrote:
> On Sun, 2 Apr 2006, Rich Adamson wrote:
> 
>>>> end-to-end path. Each step through the tracert process does nothing 
>>>> more then issue an icmp echo request, measuring the response time 
>>>> and displaying it.
>>>
>>> maybe on windows it does icmp echo but no unix does this (at least 
>>> not by default). i recommend you study what unix traceroute actually 
>>> does. :)
>>
>> I'm very heavy (professionally) into protocol analysis, and yes unix 
>> does rely on icmp to perform the traceroute. (icmp pkt type 11, code 0)
>> If you're a non-believer, put an access list on all icmp traffic and 
>> see if your traceroute continues to function. :)
> 
> 
> I said unix doesn't rely on icmp echo (might want to actually read the 
> message next time :)
> 
> I can block icmp echo and unix traceroute will function perfectly fine.
> 
> -Dan

Dan,

	Not that I want to get into this thread, but traceroute uses a mixture 
of UDP and ICMP.  It uses UDP for the initial packets and then listens 
for ICMP responses from each gateway.

man traceroute:

"
This program attempts to trace the route an IP packet would follow to 
some internet host by launching UDP probe packets with a small ttl (time 
to live) then listening for an ICMP "time exceeded" reply from a 
gateway.  We start our probes with a ttl of one and increase by one 
until  we  get  an  ICMP  "port  unreachable" (which  means  we got to 
"host") or hit a max (which defaults to 30 hops & can be changed with 
the -m flag).  Three probes (change with -q flag) are sent at each ttl 
setting and a line is printed showing the ttl, address of the gateway 
and round trip time of each probe.  If the probe answers come from 
different  gateways, the address of each responding system will be 
printed.  If there is no response within a 5 sec. timeout interval 
(changed with the -w flag), a "*" is printed for that probe.
"

ICMP echo is also COMPLETELY different from TIME_EXCEEDED.  Blocking 
echo (or echo response) is an admins choice.  Blocking TIME_EXCEEDED is 
just not very nice!

For reference:

http://www.iana.org/assignments/icmp-parameters

   0	Echo Reply				 [RFC792]
   8	Echo					 [RFC792]
  11	Time Exceeded				 [RFC792]

--
Kristian Kielhofner