Network problems on busy server

[Dima Veselov <i%kab00m.ru@localhost>]

Hello!

I have several NetBSD boxes, working for yrs, but one of them seem to be more 
loaded than others and expriencing some network issues.

Issues I have today:
1. IMAP4 mailbox, opened in mutt sometimes appear to be closed by itself
2. SSH window can close even if you work on server (when much people in the
office working)
3. Asterisk drop calls (rare, but sometimes)
4. Internet going through sometimes get slow.

Problems do not put me in trouble, however I like thing being clear and want
to configure it properly.

Main load of server caused by:
1. All the internet load of the company
2. Postfix/dovecot mail server
3. Asterisk
4. Ipfilter
5. DNS server
6. Number of IPSEC tunnels
7. Small web-server

It never has more than 1Gb memory used, never has more than 3% CPU load and
don't use swap much (59M of 4096M currently), so I assume i just meet some
limitations (network connections or something like that).

At weekend ipf state table show up 500 states, netstat -an shows about 500
lines (mostly about connected phones).  Ipf rules table says 130 lines.

Also in kernel config file i have:
maxusers        128
options         CHILD_MAX=1024   # max simultaneous processes
options         OPEN_MAX=512    # max open files per process
options         SHMMAXPGS=59400
options         SHMSEG=512
options         SEMMNI=512      # Maximum number of sets of IPC semaph
options         SEMMNS=1024     # Sys-wide max number of individual IPC
options         SEMMNU=512
options         SEMMAP=512 

options         NMBCLUSTERS=4096

This options got there because of dovecot, simply dying without that on
severe load. I have nothing in sysctl.conf.

So, the question is: is there any 'best practice' network configuration
for NetBSD on busy network? What I can do to explore the issue or if there
just a set of configuration parameters?

Thank you very much for any answer.

-- 
Sincerelly yours