Help me make sense of these traceroutes please

Pedro Cavaca pmsac.nanog at gmail.com
Wed Dec 25 00:49:30 UTC 2013


On 25 December 2013 00:03, Sam Moats <sam at circlenet.us> wrote:

> On 2013-12-24 18:55, Jeroen Massar wrote:
>
>> On 2013-12-25 00:16, Sam Moats wrote:
>>
>>> Hello Nanog community,
>>> I would like to enlist your help with understanding this latency I'm
>>> seeing.
>>>
>>
>> You are likely seeing the effects of asymmetric routing.
>>
>
> That's what I was thinking to.
>
>
>> [..]
>>
>>> Tracing route to xxx.yyy.ie [193.1.x.x]
>>>
>>
>> www.heanet.ie by chance? :)
>>
>
> Yes they were the owners of the IP I used for the example case and the
> heanet folks are actually totally awesome :-)
>
>
>
>> Though you could use for instance:
>> http://planchet.heanet.ie/toolkit/gui/reverse_traceroute.cgi
>>
>> to do a reverse traceroute, do make sure you force your connectivity to
>> IPv4 as that host will do IPv6 too. (locally nullrouting the destination
>> /128 is the trick I use for 'disabling' IPv6 temporarily).
>>
>> Otherwise the HEANET folks are extremely helpful and clued in, you can
>> always ask them for help with issues. It is the end-of-year though and
>> those Irish folks have lots of really good whiskey, Guinness thus you
>> might have to be patient till the new year.
>>
>
> Also you'd be amazed how many network issues can be solved with a bunch of
> IT folks and an ample supply of Guinness
>
>
>
>> Alternatively, you could use a tool like 'tracepath' or 'mtr' as those
>> reports multiple answers to a response and also check for the TTL on the
>> return packets.
>>
>> Greets,
>>  Jeroen
>>
>
> Thanks, this isn't affecting my service now I've worked around it so it's
> more a curiosity than anything. It seems really odd to me that the same L3
> edge router would route the ICMP unreachable back to me via different paths
> based on the final destination IP of the of the ICMP echo packet.
>
>
Based on the data you provided, my guess is some kind of MPLS transport
(please refer to
https://www.nanog.org/meetings/nanog45/presentations/Sunday/RAS_traceroute_N45.pdf,
pages 46-48).

HTH.


> Well its Christmas eve here and the customers are happy so Guinness seems
> like the best approach now :-)
>
> Thanks and have a good Holiday,
> Sam Moats
>
>
>


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