I've setup a lab with 3 routers in a hub and spoke design. R1 is the hub, R2 and R3 are spokes. IP addresses are..
X = number of router
all are /24
R1 LAN to R2 (10.0.1.X)
R1 LAN to R3 (10.0.2.X)
R1 Lo0 172.16.0.1
R1 Lo1 192.168.0.1
R2 Lo0 172.16.1.2
R3 Lo0 172.16.2.3
If I type in the command...
ip default-network 192.168.0.0
then R2 and R3 recieve this as their default route and on R1 it's marked as a candidate.
If I type in the command
ip default-network 18.104.22.168
then R2 and R3 don't install this as a default route and on R1 it isn't even a candidate. also on R1 the conf shows "ip route 172.16.0.0 255.255.0.0 172.16.2.0"
Can someone please tell me why I can't use Lo0 on R1 as a default route?
Loopback is never a valid route, and ip default-network has no practical use in real networking.
What are you trying to accomplish ?
Which Lo masks are you using all over ? R2 and 3 have 172.16.0.0 in rip database - network (rip) statement. Therefore they won't overwrite it when coming as default. They don't know about 192.168.0.0 and are fine taking it.
they're all /24. I thought that RIP v2 used subnet masks so that R2 would know it only had 172.16.1.0 and R3 would know it only had 172.16.2.0? And why does it put that statement into the running config (ip route 172.16.0.0 255.255.0.0 172.16.2.0
Please change the mask on loopback to /32. With /24 makes routers believe they all can address it natively, and generate confusion.
Could this be a subnet-zero issue?
Also, your next hop in the "ip route 172..." statement needs to be an interface address, not a network. It needs to have either the LAN address to R3 or R2 as the third address statement--"ip route 172.16.0.0 255.255.0.0 10.0.1.x".