diff --git a/IDEA b/IDEA
index 26a3bfc..e632873 100644
--- a/IDEA
+++ b/IDEA
@@ -27,3 +27,7 @@ QEMU flags:
 
 Impl: python with jinja. We want a templating engine, since most of the configs
 are the same, and something to represent computers and networks.
+
+BIRD: Router ID's are 172.23.100.<mach>, so that we have room for quite a lot
+of networks without resorting to picking canonical IP's. We might want to add
+these IP's to the hosts (as /32), but we currently do not do that.