strange denial of network

["Ilya A. Kovalenko" <shadow_(_at_)_oganer_(_dot_)_net>]

   Greetings, misc@

i386, 3.6-release, GENERIC

Once (or twice, previous time, I ask cutomer to do cold restart)
I have some strange denial of network on distant gateway. 8 hours
after boot, it stops responding (but continues to reply ARP
requests). On console it behave this way:

foo# ping 192.168.255.202
(or another, even, directly connected host)
PING 192.168.255.202 (192.168.255.202): 56 data bytes
ping: sendto: No route to host
ping: wrote 192.168.255.202 64 chars, ret=-1
ping: sendto: No route to host
ping: wrote 192.168.255.202 64 chars, ret=-1
...
foo# pfctl -Fa
...
foo# ping 192.168.255.202
PING 192.168.255.202 (192.168.255.202): 56 data bytes
ping: sendto: No route to host
ping: wrote 192.168.255.202 64 chars, ret=-1
...
foo# pfctl -d
pf disabled
foo# ping 192.168.255.202
PING 192.168.255.202 (192.168.255.202): 56 data bytes
64 bytes from 192.168.255.202: icmp_seq=0 ttl=128 time=0.452 ms
64 bytes from 192.168.255.202: icmp_seq=1 ttl=128 time=0.208 ms
64 bytes from 192.168.255.202: icmp_seq=2 ttl=128 time=0.206 ms
...
foo# pfctl -e
pf enabled
foo# ping 192.168.255.202
PING 192.168.255.202 (192.168.255.202): 56 data bytes
ping: sendto: No route to host
ping: wrote 192.168.255.202 64 chars, ret=-1
...
foo# pfctl -sa > pf.state
foo# reboot

{...}

foo# ping 192.168.255.202
PING 192.168.255.202 (192.168.255.202): 56 data bytes
64 bytes from 192.168.255.202: icmp_seq=0 ttl=128 time=0.375 ms
64 bytes from 192.168.255.202: icmp_seq=1 ttl=128 time=0.197 ms
64 bytes from 192.168.255.202: icmp_seq=2 ttl=128 time=0.228 ms
...

Any clues ?