[Asterisk-Users] Re: How is Teliax ?

[Rich Adamson]

Kristian Kielhofner wrote:
> 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


Right On!!!