The MPLS WG Archive

["Thomas D. Nadeau" <tnadeau@cisco.com>]

         Hi,

>Can anybody tell me that if LSR generate any other traps besides being "up" or
>"down" for mplsXCentry in its mplsXCTable ?

         Not that we could tell.

>What are the conditions that LSR will generate a trap when mplsXC is in "down"
>status?  In other words... if a lower layer link fails (for example SONET link
>connecting two LSR) and LSPs passing through that link are rerouted then will
>LSR still generate traps about mplsXCs being "down"?

         There are several cases where this trap is useful. First, if
you are implementing hand-routed LSPs, then one can literally disable
the label switching for that set of labels (and then re-enable them
if they so choose). In the case of auto-routed label switching, if
the label set is removed from the TFIB, then the XC is "down" --
and then disappears. The XC is "up" when it is installed.
It can also happen in the case of TE tunnels where the tunnel is using
a set of labels and might be re-routed to another set of labels, although
it is arguably easier to just monitor the tunnelEntry in the MPLS-TE-MIB.
One important use of this trap is in the case of MPLS/BGP VPN. This is a
good way of doing fault detection in the core of the network.
Using the MPLS-VPN-MIB, one can tell which LSP(s) the VPN is using
across the core. If there is a failure, one can find which VPN(s)
is/are affected because one can follow down from the VPN MIB to
the LSR MIB's XCs and go hop-by-hop along the path.

         --Tom