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

[Vincent De Keyzer]

Hello,

 

I have a customer complaining of micro-cuts during his (VoIP) phone
conversations.

 

Here is the config of his interface:

 

interface Serial6/0:0

mac-address 0014.a862.b71b

 ip address 10.11.130.33 255.255.255.224 secondary

 ip address 10.11.133.1 255.255.255.224 secondary

 ip address x.y.z.5 255.255.255.252

 ip verify unicast reverse-path

 no ip redirects

 no ip unreachables

 no ip proxy-arp

 encapsulation ppp

 load-interval 30

 no fair-queue

 no cdp enable

 ppp bridge ip

end

 

We already had similar problems a few months ago, and it was due to an
interface not being CEF-enabled - every second, the BGP scanner process
would use a lot of CPU, and delay packets being processed centrally.

 

Having that in mind, I looked at "sh cef interface":

 

BRULEOro72#sh cef interface serial 6/0:0

Serial6/0:0 is up (if_number 59)

  Corresponding hwidb fast_if_number 59

  Corresponding hwidb firstsw->if_number 59

  Internet address is x.y.z.5/30

  Secondary address 10.11.130.33/27

  Secondary address 10.11.133.1/27

  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 Serial6/0:0

  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 11(11)

  Slot 6 Slot unit 0 VC 0

  Transmit limit accumulator 0x0 (0x0)

  IP MTU 1500

 

It's the "IPv4 packets switched to this interface are dropped to the next
slow path: PPP - not open" that worries me: what does this mean ? Are the
packets CEF-switched, or not ? 

 

PPP seems to be up:

 

BRULEOro72#sh interfaces s6/0:0

Serial6/0:0 is up, line protocol is up

  Hardware is Multichannel E1

  Internet address is x.y.z.5/30

  MTU 1500 bytes, BW 1984 Kbit, DLY 20000 usec,

     reliability 255/255, txload 20/255, rxload 177/255

  Encapsulation PPP, crc 16, Data non-inverted

  Keepalive set (10 sec)

  ARP type: ARPA, ARP Timeout 04:00:00

  LCP Open

  Open: BRIDGECP

  Last input 3d15h, output 00:00:00, output hang never

  Last clearing of "show interface" counters 3d18h

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2565

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  30 second input rate 1381000 bits/sec, 172 packets/sec

  30 second output rate 157000 bits/sec, 132 packets/sec

     3059499 packets input, 1503754010 bytes, 0 no buffer

     Received 0 broadcasts (0 IP multicast)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     2965137 packets output, 2160279388 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

  no alarm present

  Timeslot(s) Used:1-31, subrate: 64Kb/s, transmit delay is 0 flags

 

This is 12.2(25)S4 on a 7206VXR.

 

Vincent