Local Loop

After getting the IP addressing on my home LAN sorted out (described in part one) I decided to tackle another unusual aspect of my setup: there is no fixed default route, instead I have M hosts on the network, and a subset of N that have wireless Internet modems, which means that at any given time there may be 0 to N number of ways to get to the Internet.

To make this work from any host on the network, I installed quagga on each machine, and configured OSPF to distribute the default routes. On one of the N possibly-Internet-connected hosts, my ospfd.conf looks like this (with the router-id set to the static IP of the host):

password secretABC
!
interface eth0
ip ospf message-digest-key 1 md5 secretXYZ
!
router ospf
ospf router-id 10.0.0.1
network 10.0.0.0/24 area 0.0.0.0
area 0.0.0.0 authentication message-digest
default-information originate metric 100
!


On the other hosts (set M minus set N), I have a similar configuration, but without the "default-information" line.

One could do this with a set of static routes, but I like this setup because it is dynamic and if I ever needed to do something fancy, OSPF has the flexibility. Now the Internet-connected hosts will advertise their default routes, and withdraw them when they disconnect.