hi
My PC is connected to an ISP with IP 192.168.1.21 on eth0
Internet works perfectly
I have installed an additional LAN card and configured it as eth1 with IP of 192.168.0.1
When I connect this LAN card to a LAN switch which in turn is connected to 6 other PCs, the internet stops working.
As soon as I switch OFF the LAN switch, I am able to access internet.
The IP addresses of the other PCs are configured as 192.168.0.2 etc. with gateway as 192.168.0.1 and DNS as the ISP DNS.
I can ping 192.168.0.1 from the LAN but neither LAN nor the main PC can access net.
I was planning to Masquerade and NAT the other computers without using squid
My main PC runs on Ubuntu 9.04 and out of the 6PCs on LAN, 2 are on Windows XP, 1 on Ubuntu 10.4, 1 on Ubuntu 9.10 and 2 on Ubuntu 9.04
Regards
Aarav

Explain to us how your internet connection and network are arranged, what protocol, router, etc.
It sounds like you have set up so you box has a choice between the internal network, or the internet. That's always going to end in tears. Can you connect the internet directly to the server?

hi
My setup is as follows
ISP - Modem(192.168.1.1) - Ubuntu desktop 9.04(external interface eth0 192.168.1.21 & internal interface eth1 192.168.0.1) - switch - LAN (comprising of Ubtuntu 9.04, 9.10, 10.4 & XP machines with IP 192.168.0.2 - 8 and gateway of 192.168.0.1)
I did NAT as per https://help.ubuntu.com/community/In...nectionSharing
This worked perfectly well 1 day
Next day onwards whenever the LAN switch is "ON" the main Ubuntu wudnt get internet and the internet connection would work only when the LAN switch is turned "OFF". Even if all the PCs in LAN were to be switched off, the main Ubuntu would behave similarly i.e. internet would work only when switch isn't connected to it or switched off.
regards
Aarav

OK. Modem on 192.168.1.1 is doing dhcp? If it's on pppoe it's not inclined to change the external IP. I really don't like that all your network is 192.168.0.nn, whereas your internet is on 192.168.1.nn. I'd make mistakes with that sort of thing.

for the record, run(on box with the internet, & 192.168.1.1)
cat /proc/sys/net/ipv4/ip_forward
It will say 0 or 1. If it says 0, try
echo 1 > /proc/sys/net/ipv4/ip_forward, and put that in rc.local.
Then I would go for the laziest of options. On 192.168.1.1 & 192.168.1.21, make an entry in /etc/hosts describing the other. These are 'known hosts' that your box may try in it's search path. If that doesn't sort it, post resolv.conf files from 192.168.1.1 & 1.21

hi
cat /proc/sys/net/ipv4/ip_forward gives an output of 1
I had to disconnect this PC from the LAN to access internet and post this reply
If not 192.168.0.nn then which series should I go in for ?
Modem on 192.168.1.1 is doing dhcp
Kindly help
regards
Aarav

It seems like there is problem with the default gateway when you set up your LAN. Your machine default route should point to your ISP gateway with ip_forward=1 enabled in your machine for other LAN clients access the internet. It would be good if you can post the output of the following,

netstat -rn

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Prasanta