send_query: No buffer space available

[Pertti Kosunen]

What should i do to avoid these messages from MRTG and dhclient? This 
happens with some network load on xl0 interface and pf+altq or 
ipfw+dummynet+statefull rules enabled, even with simple pass rules.

Increasing kern.ipc.nmbclusters, kern.ipc.nsfbufs, kern.ipc.somaxconn 
and net.inet.tcp.sendspace doesn't seem to help. FreeBSD 5.3-RELEASE to 
6.0-BETA5 have this problem.

SNMP Error:
send_query: No buffer space available

dhclient: send_packet: No buffer space available

netstat -m
1108/572/1680 mbufs in use (current/cache/total)
975/351/1326/17216 mbuf clusters in use (current/cache/total/max)
0/12/4560 sfbufs in use (current/peak/max)
2227K/845K/3072K bytes allocated to network (current/cache/total)
0 requests for sfbufs denied
0 requests for sfbufs delayed
94 requests for I/O initiated by sendfile
766 calls to protocol drain routines