[nsp] Dial-Backup for PPPoE-Dialer?

Tim Franklin tim at colt.net
Fri Feb 13 11:06:59 EST 2004

cisco-nsp-bounces at puck.nether.net wrote:
> In terms of portability, using SAA to track a specific IP address and
> therefore bring up the ISDN if that IP address is down seems just as
> unportable as dialer-watch tracking a specific IP address.

Yes.  What you could do is configure either of those mechanisms to watch something that doesn't go away unless things are Very Broken, but is the same "something" for every router, everywhere.  Maybe put a loopback in every PoP or even on every access router that has no purpose other than to be an "is my link up?" ping target for CPE devices.

(ISTR Demon doing this way-back-when with, as a customer self-diagnostic measure rather than a monitoring tool, but the same idea.  I'm sure a number of other people have thought of it too, but I think that's where I first saw it...)

> Surely the
> most portable way is to use a /30 on the connection in the first place
> and track
> the /32 peer neighbor-route, otherwise you end up changing SAA
> instead of the dialer-watch feature on every router. Obviously you
> trade IP space wastage for portability, but this might be alright in
> some circumstances (MPLS VPN for example).

/30 point-to-points are good for diagnostics in general.  /31s are better, if everything you have groks them correctly.


Tim Franklin          ____________
Project Engineer      \C/\O/\L/\T/   Product Engineering &
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