Re: Long round trip times on local net

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Thu, 12 Feb 2009 00:50:50 +0000
raymond.meyer%rambler.ru@localhost wrote:

> I have two machines running NetBSD-5 beta, i386 and sparc64. Both
> machines are on a local network. When I ping i386 machine from
> sparc64 I notice the following output:
> 
> 64 bytes from 192.168.0.40: icmp_seq=49 ttl=255 time=0.261 ms
> 64 bytes from 192.168.0.40: icmp_seq=50 ttl=255 time=0.254 ms
> 64 bytes from 192.168.0.40: icmp_seq=51 ttl=255 time=1000.276 ms
> 64 bytes from 192.168.0.40: icmp_seq=52 ttl=255 time=0.416 ms
> 64 bytes from 192.168.0.40: icmp_seq=53 ttl=255 time=0.258 ms
> 64 bytes from 192.168.0.40: icmp_seq=54 ttl=255 time=1000.250 ms
> 64 bytes from 192.168.0.40: icmp_seq=55 ttl=255 time=0.391 ms
> 64 bytes from 192.168.0.40: icmp_seq=56 ttl=255 time=0.256 ms
> 64 bytes from 192.168.0.40: icmp_seq=57 ttl=255 time=0.264 ms
> 64 bytes from 192.168.0.40: icmp_seq=58 ttl=255 time=0.275 ms
> 64 bytes from 192.168.0.40: icmp_seq=59 ttl=255 time=0.257 ms
> 64 bytes from 192.168.0.40: icmp_seq=60 ttl=255 time=1000.249 ms
> 64 bytes from 192.168.0.40: icmp_seq=61 ttl=255 time=0.386 ms
> 64 bytes from 192.168.0.40: icmp_seq=62 ttl=255 time=0.264 ms
> 64 bytes from 192.168.0.40: icmp_seq=63 ttl=255 time=1000.248 ms
> 64 bytes from 192.168.0.40: icmp_seq=64 ttl=255 time=0.388 ms
> 
> Quite a few packets show round trip time of just over a second. If I
> ping sparc64 machine from i386, the round trip time for all packets is
> about 0.200 ms, i.e. there are absolutely no over 1 second delays.
> 
> Does anyhone know why so many packets have such long delays? The i386
> has a PCI network card that uses rtk driver, sparc64 uses hme driver.
> I've tried different CAT cables on both machines, which didn't make
> any difference. Can this be a hardware problem or a driver bug?
> 
Are you doing 'ping' or 'ping -n'?  I wonder if it's a DNS lookup issue
-- those figures are very suggestive of a 1-second timeout.

Hmm -- I wonder if an interrupt is getting lost.  That 1 second is the
interval to the next ping, after all.  Try it with '-i 5' and see if
you get 5-second delays.  Try it with another transmission (say, via
ttcp) running in the background and see if that gets rid of the delays.


                --Steve Bellovin, http://www.cs.columbia.edu/~smb