[j-nsp] icmp problems tracing through m20's

[variable at ednet.co.uk]

On Thu, 22 May 2003, David Brazewell wrote:

> has anyone ever experienced problems where icmp traces (using mtr) to 
> destinations through an m20 show no packet loss at the last hop but 
> varying amounts of packet loss on one of the juniper interfaces?

Hi Dave,

Unless you've cranked up the packet rate on MTR (from the default 1 packet
per second), I wouldn't have thought that the rate limiting would be a
factor on this unless you specifically set the rate limit really low (the
defaults shouldn't be an issue).
 
> tracing to the juniper itself shows no packet loss.

Have your tried running mtr with the -n flag to make sure that the packet
interface you are seeing that packet loss on is the same one as the one
you are tracing to directly?  Do you have default-address-selection
enabled?  Might also be worthwhile either setting up a filter to log ICMP
packets from the IP you're running MTR from and/or tcpdumping the LAN
segment(s) it's on to make sure the packets are making all the way to the
M20.

Do you monitor the load on the M20?  Is it busy?  Does show system
statistics icmp show any other reasons for drops other than rate limiting?

HTH,

Rich