[K12OSN] [OT]router howto

"Terrell Prudé, Jr." microman at cmosnetworks.com
Sun Jul 24 15:34:55 UTC 2005

First, we've got to see if your routing parameters in your DHCP scope 
are right.  Have your DHCP clients ping the  router that is upstream 
from your GNU/Linux router; this will be your ISP's router, probably a 
Cisco or Juniper router of some sort.  I'm assuming here that your 
GNU/Linux router is directly connected to your ISP with nothing else 
(cable modem, DSL router, other firewall, etc.) in between.  If that 
doesn't work, then make sure that your GNU/Linux router can get to it; 
if it can't, then nothing will be able to.  If it can, though, then 
check your IP Masquerading rules.  This assumes you're using RFC 1918 
"private" IP addresses; if not, then don't worry about masquerading rules.

Once all that's working, then we've got to try connectivity past your 
ISP's router.  Try pinging an IP address instead of a domain name.  A 
good one is, which is one of UUNet's main DNS servers.  If you 
can, then the problem probably is the DNS server parameters in your DHCP 

My guess is that, once you get connectivity to your ISP's router from 
your clients, then going to the Internet will also work.


Dale Sykora wrote:

> This is slightly off topic, but I thought I'd ask as this list is 
> usually very helpful.  I am having trouble trying to setup a generic 
> fc4 or centos4 into a network router.  eth0 goes out to the internet 
> and eth1 goes to the internal network.  Internal systems can get an ip 
> from the server and can ping the server, but they cannot ping anything 
> on the internet such as yahoo.com.  I tried enabling ip_forward in 
> /etc/sysctl and tried comparing settings with a SME server, but I 
> can't figure out what I am missing.  Any suggestions on what I should 
> check next?
> Thanks,
> Dale
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