Recommendation of Tools

Anders Lindbäck list-only at dnz.se
Wed Dec 3 16:14:23 CST 2008


Well, to be somewhat cynical about it, you don't.

Either you have an SLA with a delay component, if that is the case  
the delay is either end-to-end if everything is in the same AS, or  
host-to-border if the other end is in some other AS. If this is the  
case you would already have an agreed upon measuretool (ex. SLA  
probes) and specified measuring points.

If you dont have a specified delay clause in your SLA then it is best  
effort and irrelevant, in either case the hop by hop delay seen is  
academic at best..

So as long as your delay is lower then specified by the SLA the only  
result from trying to be "smart" and complaining about large hop to  
hop delay is that the engineer you talk to will call you names after  
he/she hangs up, or if it is over it is still very little/nothing you  
can do but wait and let the carrier engineers fix it.

------------------------------
Anders Lindbäck
anders.lindback at dnz.se


On 3 dec 2008, at 20.56, Braun, Mike wrote:

> If the question is to measure hop by hop latency from source to  
> destination, perhaps across routers you don't manage, how can this  
> be done without using the ICMP time exceeded messages?  End to end  
> latency is easily done with Smokeping and the use of TCP (SYN, SYN  
> ACK, ACK, RST) and them timestamp it.  This gives you a very clear  
> idea on application latency on any tcp port.  Hop by hop is a  
> different story and the only option I know of is with the reliance  
> on the ICMP mechanism.  One additional question on this; how do you  
> measure hop by hop when the path dynamically changes, and then  
> record the path change (time/date and the differences in latency on  
> the new path)?
>
> Mike
>
> -----Original Message-----
> From: Anders Lindbäck [mailto:list-only at dnz.se]
> Sent: Wednesday, December 03, 2008 10:02 AM
> To: Pekka Savola
> Cc: nanog at nanog.org
> Subject: Re: Recommendation of Tools
>
> Mtr is even less usefull then that, in its default mode it does a
> traceroute and then proceeds to ICMP Ping flood each IP in the list
> generated by the traceroute, the result is usually completly useless
> on WAN topologies due to asym-routing, ICMP node protections by
> carriers and punting etc..
>
> And using UDP will not really provide better results due to the same
> thing, and IIRC Cisco from 12.0 has a standard setting of no more
> then 1 ICMP Unreach per 500ms..
>
> ------------------------------
> Anders Lindbäck
> anders.lindback at dnz.se
>
>
> On 3 dec 2008, at 12.00, Pekka Savola wrote:
>
>> On Tue, 2 Dec 2008, Antonio Querubin wrote:
>>> On Wed, 3 Dec 2008, Pekka Savola wrote:
>>>>  FWIW, Mtr measures latency/delay and loss based on ICMP messages
>>>> heard
>>>>  back from the routers on path.  As a result, in almost all
>>>> cases, the real
>>>>  hop-by-hop latency of actual end-to-end data packets is better
>>>> than it can
>>>>  report.
>>>
>>> mtr has a recently added '-u' option to use UDP instead of ICMP
>>> echo requests.
>>
>> But that doesn't change the gist of my message: it's still relying
>> on ICMP ttl exceeded messages sent by the routers on the path to
>> check the delays etc.  As such it suffers from basically the same
>> limitations as ICMP probing.
>>
>> -- 
>> Pekka Savola                 "You each name yourselves king, yet the
>> Netcore Oy                    kingdom bleeds."
>> Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
>>
>
>
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