barak-online.net icmp performance vs. traceroute/tcptraceroute, ssh, ipsec
ltd at interlink.com.au
Tue May 8 04:12:57 UTC 2007
> Anyways, initial reports are that as per my advice, customer calls
> vendor says "voip not working" vendor says "i changed something, wont
> tell you what, reboot everything in 30" and now things seem to work
> perfectly, strangely enough EVEN the traceroutes.
> This is obviously not best effort. Best guess would be "managed
> bandwidth" differentiated by ip ranges and that the "change" was a
> different pool assignment.
its hard to say. could be that a peering connection was down or congested,
that cold-potato routing within said provider was suboptimal, there are any
number of rational reasons other than "managed bandwidth".
> I suspect the stellar icmp echo performance is also intentional.
as stated previously, eliciting a response out of a router through "icmp
processing" is vastly different to the standard process of forwarding a packet.
there are any number of countless reasons why icmp-ttl-exceeded response times
can be vastly-over or vastly-under the actual round-trip-time of a packet.
if you still don't believe, do a search for "Cisco Control Plane Policing" or
other vendors have similar mechanisms also.
> tcptraceroute lsvomonline.dnsalias.com -q 5 -w 1 80 -f 7
> Selected device eth0, address 192.168.0.3, port 33204 for outgoing packets
> Tracing the path to lsvomonline.dnsalias.com (22.214.171.124) on TCP port
> 80 (www), 30 hops max
> 7 kar2-so-7-0-0.newyork.savvis.net (126.96.36.199) 45.008 ms
> 52.978 ms 32.404 ms 50.676 ms 33.657 ms
> 8 dcr3-ge-0-2-1.newyork.savvis.net (188.8.131.52) 49.037 ms 33.145
> ms 48.029 ms 34.355 ms 48.453 ms
using tcptraceroute in this manner is NO DIFFERENT to normal traceroute.
the routers in the intermediate hops are still essentially doing
icmp-ttl-exceeded behaviour, so the same "can't read anything into the latency"
statements i've made a few times now.
in either case, its good to hear you have your issue resolved.
More information about the NANOG