L3 keepalives without routing protocol?

[Andy Harding]

Hi all,   strange problem for y'all...   I have a problem whereby a down circuit does not necessarily "down" an interface (via ATM switch - am using OAM but not foolproof).  Is there some way that I can enable a L3 keepalive without running a global IGP (bear in mind that this is between my core routers and several thousand 25XX/26XX clients, and I don't want to give them a routing table, just a default route).   We run a NOCOL-type daemon that alerts me if a machine has been unpingable for >15 minutes, but am looking for a sure-fire way to have a core router send the NMS a trap when a circuit becomes unreachable at L3.   any help much appreciated as always   Andy