On 25 December 2013 00:03, Sam Moats <s...@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 > > >
