[NTLUG:Discuss] Troubleshooting when you lose the Internet (2 questions)

[Jack Snodgrass]

On Sat, 2003-02-22 at 13:15, Rick Matthews wrote:
> Everybody knows that "stuff happens" on the net.  I'll click a link 
> from a search engine and it will be slow (or dead).  No big deal.
> I may click another link and find it in the same shape.  Depending 
> on what I am doing at the time, it may take several bad clicks before
> my brain snaps to and realizes that it may not be the links.  I'll 
> click on a "known good" site, and if that is unsuccessful I'll 
> try another.  But when my email client then tells me that it is 
> unable to contact my external pop3 server, I'm sure there is a problem.
> Now what do I do?
> 
> My ADSL is connected to eth0 in my Linux firewall box; eth1 connects
> to a LinkSys switch and then to Windows boxes.  The Linux box also 
> runs Squid, squidGuard, and Apache (internal only, serves reports, 
> docs, and squidGuard redirect pages).


Generally, when you 'reboot and network things start working again', 
it's a DHCP problem. You might be able to accomplish the same 
results without rebooting by doing a /etc/rc.d/init.d/network restart
( on redhat anyway. Your distribution should have a similar command
line call to tell your networking to stop and restart. ) You don't
need to do a full reboot just to restart your network. 

A even less drastic approach ( you may loose some network 
connections if you restart your network in the middle of a file 
transfer or other type of network link ) would be to send a SIGHUP
to your dhcp client process. This will tell the client to renew 
it's IP Address. The process for doing this depends on your 
dhcp client. 

Other things you can do to debug this is to run traceroute ( or 
mtr - a better replacement ) to different addresses ( your ISP 
and / or favorite sites ) and see what happens with that. It's 
generally a good idea to do this when things work ( and maybe
print off the results ) and do this when things don't work. 
You might see if it's you, your isp or your isp's isp that
is having the problem. 

jack