R2R NHRP - ensuring far end is alive

["M.J. Robinson" <[e-mail]>]

Yakov (and other ROLCers),
	Your current R2R approach requires that "Once a shortcut is 
established, the Requester needs to have some mechanism(s) to ensure that 
the other end of the shortcut is alive."
	Possible mechanisms suggested are:
(a) indications from the Data Link Layer
(b) prescence of traffic in the reverse direction that comes with the Link 
Layer address of the other end
(c) keepalives sent by the other end

	In some situations, keepalives may be the only option. 
Additionally, a "hello" time (meaning as for OSPF) of the order of 10
seconds might be required/desired. (For instance if IP encapsulated SNA is
being sent to a mainframe which has two connections to the NBMA (for
redundancy) ).
	I'm trying to understand how things would behave under such
conditions. Especially, what is the impact of such a high rate of
keepalives likely to be on both the network and routers ? 
	Thanks,

		Matthew Robinson.