Arch Linux

lykwydchykyn

Member

Registered: 2013-07-11

Posts: 91

using my laptop as a router

I sometimes use my laptop as a router for one of my machines that isn't connected to a network, so that I can run updates etc.  I used to do this successfully on my old laptop running Kubuntu, but now on Arch I'm having trouble getting it working.

The computer runs Debian squeeze and connects to the laptop via cable on eno1.   The laptop is connected to my wireless network on wlp3s0.

I have dnsmasq installed and configured as follows:

interface=eno1
except-interface=wlp3s0
bind-interfaces
dhcp-range=192.168.0.50,192.168.0.150,12h
dhcp-option-force=208,f1:00:74:7e
dhcp-option-force=209,configs/common
dhcp-option-force=210,/srv/tftpboot/
dhcp-option-force=211,30i
dhcp-boot=pxelinux.0
enable-tftp
tftp-root=/srv/tftpboot

Then I have this script which sets up routing:

#!/bin/bash
LAN_NIC=eno1
WAN_NIC=wlp3s0
sudo ip addr replace 192.168.0.1/255.255.255.0 $LAN_NIC
sudo systemctl start dnsmasq
sudo iptables -t nat -A POSTROUTING -o $WAN_NIC -j MASQUERADE
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward

After running these:

- eno1 isn't getting its IP via the script, but I was able to manually set it using NetworkManager, so that's not important right now
- DHCP is working, because the deb box gets an IP in the correct range
- The deb box gets a default gw of 192.168.01.  I can ping the default gw.
- I can resolve hostnames from the deb box, so DNS is working.
- /procy/sys/net/ipv4/ip_forward is indeed 1
- the output of iptables -L is this:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere             udp dpt:bootps
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:bootps

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             192.168.122.0/24     ctstate RELATED,ESTABLISHED
ACCEPT     all  --  192.168.122.0/24     anywhere            
ACCEPT     all  --  anywhere             anywhere            
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination  

(the 192.168.122.0 stuff is related to libvirt, I believe).

however

- I can't ping anything beyond the default gw from the deb box.  I get the first packet back with something about "Redirect Host", then Destination Host Unreachable for the rest of the packets. 
- I can't download anything.  It just says "no route to host".

What am I missing here?

lykwydchykyn

Member

Registered: 2013-07-11

Posts: 91

Re: using my laptop as a router

Well, I got it working; I deleted eno1 from network manager's clutches, then set it's IP with good ol' ifconfig.  Works just fine.

Can't figure out why the ip addr command doesn't seem to work, but hopefully ifconfig will stick around for a few more years.