Strange Networking Problem

[Sten Spans]

I recently upgraded an 164SX ( ev56 ) to 5.2.1
and I am experiencing some strace network problems.

The box stops forwarding ipv4 traffic after
some time, ipv6 still works.

towel# ping bastard
PING bastard.snore.nl (62.250.7.5): 56 data bytes
ping: sendto: No buffer space available
^C
towel# ifconfig fxp0 down
towel# ifconfig fxp0 up
towel# ping bastard
PING bastard.snore.nl (62.250.7.5): 56 data bytes
64 bytes from 62.250.7.5: icmp_seq=0 ttl=61 time=1.927 ms

netstat -m shows plenty of mbuf space available.
Any hints are appreciated.

-- 
Sten Spans

"There is a crack in everything, that's how the light gets in."
Leonard Cohen - Anthem