Gateway through iptables (shorewall)

Deathwing00

I want my desktop computer to serve as gateway to my laptop. I have 2 ethernet cards on my desktop computer (eth0: LAN and eth1: NET). I have managed to configure iptables with shorewall so my desktop PC assigns a dynamic IP to the laptop (DHCP) and it works.
The PROBLEM is that if I don't ping the laptop, the access of the laptop to the net doesn't work. I'd like to know if there is a reason for this and how I can solve it. Also, after certain period of innactivity, I mean that the laptop stops using internet for a while, then when I try to make a connection, the desktop pc doesn't respond to it. It's a very strange behaviour... is anyone so intelligent to help me with this?

devon · l33t Joined: 23 Jun 2003 Posts: 943

Don't know if anyone has helped you with this.

What I think may be happening is an ARP problem. When you ping the laptop, the gateway makes an entry in it's ARP table for the laptop's hardware address. After a certain amount of inactivity, that entry expires. Now why doesn't the inital packets from the laptop to the gateway make that ARP entry? I have never used Shorewall, but perhaps the settings are a little strict (regarding Ethernet frames)?

To see if what I suspect is happening, you can do the following:

1. Wait till the laptop stops working.
2. Do a "/sbin/arp -n" on the gateway.
3. You should not see an entry for your laptop (look for the IP address you assigned it).
4. Ping from the gateway to the laptop.
5. You should now see an entry.
6. Wash, rinse, repeat.

Sample "/sbin/arp -n" output

Deathwing00 · Posted: Mon Jun 23, 2003 10:59 pm Post subject:

Sorry! I already solved the problem by myself and forgot to post it here!!! :oops:

Just followed the Installation docs (route add -net default gw xx.xx.xx.xx netmask 0.0.0.0 metric 1 eth0)