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Posted by Stephen on June 7, 2008, 7:06 pm
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>Hi all
>
>consider the following situation:
>
>Customer edge Router (e.g. Cisco 28xx) with a primary link to the
>provider edge router via an Etherconnect line, i.e. a connection where
>the carrier provides a modem which is conected to the router.
>A backup link is established over a steady DSL connection. On both
>interfaces we have /30 transfer networks an run ospf with the provider
>edge routers on the other ends.
>
>Now we want to monitor the primary connection from the provider
>backbone. Usually we do not use ospf and simply ping the customer edge
>IP adresses of the two transfer networks in order to test their
>reachability.
i think you are ruling out the best way to do this - routing protocols
are there to check reachability (as well as other things) - so why not
use it?
>Now in case of the running ospf this is not an option since both IP
>addresses would be always reachable as long as one connection is up.
Nope - far end address across the link is not "up" from your
perspective unless the link works and you have 2 way packet exchange.
Near end may stay up though - in which case you are pinging the wrong
object.
>
>An option would be to monitor the interface status via snmp. That's good
>as long as a failing connection implies an interface status change to
>down. Unfortunately this is not the case since the connection to the
>carrier's modem would always be up.
>
>Well, I've read a lot about tracking objects and routing policies but
>I'm not sure whether or not (and if yes, how exactly) this would be of
>any help in this case.
BFD may work as another suggested - but you need modern devices / code
at both ends since this is fairly recent.
cisco have a way of linking "reachability" into statics using SAA /
RTR or whatever it is called now
http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtpbrtrk.html
>
>Any suggestions?
>
>Thanks a lot in advance,
>
>Grischa
--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl
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