Dealing with UK lease line WAN circuit suppliers (well BT and Virgin) I always have to program the WAN interface of the MK with a mask of at least /29 (and sometimes /28) where as the documented subnet mask from the supplier is always 255.255.255.254 (/31). The Aggregation router is always the next ip up. CPE IP x.x.x.246 and AR IP x.x.x.x.247 yet I can only ever bring up the route if I use /29 (/28) as the network mask.
Anyone else have this issue? Its never been a problem because Ive never had a customer with two circuits in the same location at the same time but one day Im going to hit a hurdle of having another circuit on say .248 (in the above example) and Im not going to be able to route to it.