Hi guys,

Are interfaces Serial 0/0 and Serial 0/0.1 different network types ?

Thanks :-)

When you use multipoint access or point to multipoint you should have virtual interfaces so when a peer is down you don't have routing problems. Split horizon is a problem if you don't use subinterfaces.

Kind regards

For OSPF:

http://deepakarora1984.blogspot.com/2010/02/mixing-matching-different-ospf-network.html