[c-nsp] "Packets dropped to the next slow path"

[Mark Newton]

Vincent De Keyzer wrote:
> Ok,
> 
> looking at the list archive (which I should have done right from the start,
> shame on me), I see that this could be due to a feature not supported by
> CEF.
    [ ... ]
> What is it? PPP half-bridging? How do I find out?

I have an open TAC case at the moment which is working through the
fact that if you have a serial interface on a router with "ppp bridge ip"
set, MPLS will direct traffic which ought to be sent out via that
interface through some random other interface instead.

(it's case number 602402373, just in case any helpful Cisco folks are
reading this and want to fix the bug for me :-)

It happens due to the fact that CEF can't work out an adjacency for
the device at the other end of the serial interface because it doesn't
know its IP address until PPP has successfully negotiated IPCP, but
when PPP is bridging Ethernet frames it doesn't actually care about
IPCP and never quite gets around to doing it.

The workaround was to create a recursive route so that CEF has something
to hang its hat on:

   interface Serial1/0
    ip address 192.168.1.1 255.255.255.252
    ppp bridge ip
   !
   ip route 192.168.1.2 255.255.255.255 Serial1/0

Once CEF sees the static route via the interface, MPLS on all the
*other* interfaces magically starts working.

See if it fixes your problem too.

    - mark

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I tried an internal modem,                    newton at atdot.dotat.org
      but it hurt when I walked.                          Mark Newton
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