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

[Jason Philbrook]

I'd have them to check to see if there are any cheap firewalls/routers
between their phone and your router. A QOS enabled firewall (even a $55
linksys wrt54g will do when using ethernet) is often necessary to
prioritize voice over other traffic they may be generating.

On Mon, Nov 21, 2005 at 02:39:32PM +0100, Vincent De Keyzer wrote:
> 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
> 
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