Thursday, August 21, 2008

Slackware 12.0 - Dual Homed

Challenges can arise when a wifi NIC is handling wifi internet access and, in the same computer or "host", an ethernet NIC is operating in a wired LAN (eg, with a printer and backup storage). Since the host exists in two different LANs simultaneously, it is "dual homed". Obviously, two LANS means two routers.

gateway vs. dhcpcd

Check email at Yahoo. The host PC makes this request to Yahoo and Yahoo is outside the host's network, so it needs to use the gateway and the name servers outside the gateway. But when interfaces are being initialized at boot, the dhcp application, dhcpcd, overwrites the /etc/resolve.conf file that shows the IP addresses of these nameservers. So, if we bring the eth0 connection up after the wlan0 connection, our nameservers will be overwritten. To avoid this we do all these things:
ifconfig eth0 down
ifconfig wlan0 up
dhcpcd wlan0
sleep 3
sleep 5
route del -net netmask dev wlan0
ifconfig eth0 up
sleep 3
dhcpcd -R eth0 #-R prevents resolv.conf overwrite
sleep 3

Sometimes,(rare) I have a "UG" default gateway for both wlan0 and eth0 even after these steps. I then remove the extra gateway at the command line:
route del default eth0
A quick verification with "route" shows me the second gateway is gone.
Also there are these files...

loading order

rc.inet1 reads rc.inet1.conf and loads rc.wireless which reads rc.wireless.conf when loading. I don't worry about the rc.wireless.conf, but, in rc.inet1.conf I look for the default gateway line and I change it from "" to the IP of the gateway router.


The final step. We want to be sure everything is running before we lock down ports.

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