External Network Change

Bob Chiodini rchiodin at bellsouth.net
Fri Jul 22 17:37:32 UTC 2005

On Fri, 2005-07-22 at 10:24 -0700, Patrick Nelson wrote:
> FC3 (all up to date)
> This may seem simple but I'm changing ISPs and I have 2 internet facing 
> systems that also connect to the private network.  One being the GW the 
> other being Mail.  So I have the gateway working fine but I can not get 
> the mail server working in the changed network config.  I just want to 
> make sure I'm not missing anything, because I think that the ISP is not 
> routing, switching, or configured correctly.
> -The two systems are attached to a Hub along with the connection to the 
> Internet.
> -The gateway system is working fine with the new ISP changes (serves as 
> the DNS and GW)
> -The mail server can be configured with the new ISP, but once I do that 
> system can not ping the internet
> --however it can ping the internet side of the GW
> --and the intranet.
> -With ethereal I sniffed the mail server connection and it does appear 
> to get anthing back from the ISP GW
> Here are the changes that I make to mail server:
> 1. Use system-config-network to change the:
>  -IP Address
>  -Subnet Mask
>  -Gateway
> 2. Change the IPTables Firewall Script to match the new config
> 3. Turn off the firewall script for the first booting in the new network 
> config
> 4. Reboot
> The booting goes fine but I can not ping anything other than the GW 
> system on the Internet side.
> Is there anything that I'm missing or might try?  Or does this sound 
> like a routing problem on the side of my ISP?


Post the output of ifconfig and route -n from both machines.  It sounds
like the default gateway on the mail server is incorrect.


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