RH 6.1
Dell Inspiron 3500
D-Link DMF-560TX combo ethernet/modem pcmcia card

Begin with system functioning normally. Ping a host on the
same ethernet segment, see normal ping times (less than
1ms).

Disconnect twisted pair ethernet cable for a few seconds,
then reconnect. Ping times are now 1000 msec + a fraction
of a msec, i.e., exactly 1 second late. Other network
performance (e.g., nfs, etc.) becomes terrible.

execute "ifconfig down up". Ping times return to normal
and other network performance returns to normal.

This behaves like an off-by-one buffer pointer problem
triggered by link-down/link-up. Maybe a packet doesn't
get transmitted until another packet gets queued behind it.