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

[Vincent De Keyzer]

So that would be the meaning of the end of the message ("PPP - not open"):
it is routing via the processor because PPP was not open yet at the time CEF
looked at the interface?...

Unfortunately your fix does not work for me (or I misunderstood it):

interface Serial6/1:0
 mac-address 0014.a862.b71b
 ip address x.y.z.225 255.255.255.248
 ip verify unicast reverse-path
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 encapsulation ppp
 load-interval 30
 no fair-queue
 ppp bridge ip
 no clns route-cache

ip route x.y.z.226 255.255.255.255 Serial6/1:0


BRULEOro72#sh cef int s6/1:0
Serial6/1:0 is up (if_number 61)
  Corresponding hwidb fast_if_number 61
  Corresponding hwidb firstsw->if_number 61
  Internet address is x.y.z.225/29
  ICMP redirects are never sent
  Per packet load-sharing is disabled
  IP unicast RPF check is enabled
  Input features: Verify Unicast Reverse-Path
  Inbound access list is not set
  Outbound access list is not set
  IP policy routing is disabled
  BGP based policy accounting on input is disabled
  BGP based policy accounting on output is disabled
  Interface is marked as point to point interface
  IPv4 packets switched to this interface are dropped to the next slow path:
PPP - not open
  Hardware idb is Serial6/1:0
  Fast switching type 7, interface type 13
  IP CEF switching enabled
  IP CEF switching turbo vector
  IP CEF turbo switching turbo vector
  IP prefix lookup IPv4 mtrie 8-8-8-8 optimized
  Input fast flags 0x4000, Output fast flags 0x0
  ifindex 12(12)
  Slot 6 Slot unit 1 VC 0
  Transmit limit accumulator 0x0 (0x0)
  IP MTU 1500

BRULEOro72#sh ip cef adjacency serial 6/1:0 x.y.z.226
(shows nothing)


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