[H-GEN] intermittent cable connxn outage

[Troy Piggins]

Hi.  I posted this today on comp.unix.admin, but need help real
quick.  This internet not working is crippling business (aint it
always )

I am totally stumped by this, and seek some advice on either a
solution or possible course of action to locate the problem.

The problem is that just yesterday and today the connection to
internet is only working intermittently.  By this I mean that it works
for hour or so, then can't see anything outside (ping, DNS etc), then 
it works for a while, then not.

I have not installed anything new these last couple of days.  Week
or 2 ago I installed apache2 from 1.3, but I don't suspect that.

I run a RH9 box as a gateway/NAT/firewall for a small office
network.  It has been running fine for about a year.  Services include 
iptables (with NAT and the only open external port is ssh 22); imap, 
pop, and sendmail; http (apache2), samba, squid - there are others, 
but don't suspect any of them.  It connects to the internet via one 
of its 2 NICs connected to cable modem, and the external IP is dynamic 
(DHCP).

All services - http, ssh, samba etc work fine from the inside
network, it just seems to be anything that uses the external interface.

Because it comes and goes I thought maybe a cron job(?).  No new
jobs though in last few days.  Each user (about 12) has only 1 cron 
job set up to fetchmail every 15 mins.  I changed that to 1/2hr to 
see if large emails clogging it up, but that hasn't solved anything.

Another thought was that it could be hardware - network card playing
up, or even the modem?  I don't know how to check this.  I don't have a
spare modem.

Could be a DOS attack?

I can't ping IP address or URLs (when it is not working).  When it
works DNS resolution etc is fine.  I spoke to ISP and they don't know 
of any problems in the area.  Oh, and as soon as I mention the gateway 
is linux, they say "we don't support linux, windows only" and 
conversation ends shortly after :-(

I am not a linux admin or guru, but I have been a linux user for some 
years so know the basics. I have set up this box with all its services 
and noone else knows  how to use linux in the office.

Any help appreciated.
-- 
T R O Y  P I G G I N S
e : troy at piggo.com