Process and Hardware Switching

Unanswered Question
Jan 14th, 2009

CEF is enabled on the interface yet I only see processor packet counts below and not route cache. Please explain why is that.

SWITCH#sh int stats

GigabitEthernet4/1

Switching path Pkts In Chars In Pkts Out Chars Out

Processor 0 0 45516 21001468

Route cache 0 0 0 0

Distributed cache 0 0 0 0

Total 0 0 45516 21001468

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Richard Burts Wed, 01/14/2009 - 10:36

The prompt indicates that this is a switch. Switches use ASICs and do much of the forwarding in hardware. The packets that are switched in hardware do not show up in the interface stats.

HTH

Rick

cisco_lite Wed, 01/14/2009 - 10:40

It is a CAT6500 switch and ip cef is enabled on all the interfaces.

Wouldn't route cache be considered as hardware switched. And what does processor count in the given output mean.

Thanks.

Richard Burts Wed, 01/14/2009 - 10:49

no route cache (nor CEF) is not considered hardware switching. hardware switching is when the ASIC on the switch makes the forwarding decision.

HTH

Rick

Jon Marshall Wed, 01/14/2009 - 10:51

Route cache is associated with fast switching which is not CEF. 6500 don't use fast-switching.

Processor would be the Route Processor ie. the vast majority of packets are hardware switched on a 6500 using the PFC (Policy Feature Card). Those that can't be hardware switched are sent to the processor (MSFC) to be dealt with by the main CPU.

Jon

Richard Burts Wed, 01/14/2009 - 11:16

That article was written from the perspective of IOS "routers". In particular remember this note from the beginning of the article:"Note: This document discusses process switching, fast switching, and Cisco Express Forwarding (CEF) only." It explicitly indicates that it does not discuss hardware switching (on Catalyst switches).

Within its frame of reference the article is correct and helpful. But your question is an aspect that is outside the scope of the article.

HTH

Rick

Jon Marshall Wed, 01/14/2009 - 11:20

Can you post output of

"show interfaces gigabitethernet 4/1 | include Switched"

Jon

cisco_lite Wed, 01/14/2009 - 11:37

Cisco IOS Software, s72033_rp Software (s72033_rp-ADVIPSERVICESK9_WAN-M), Versio

n 12.2(33)SXH3, RELEASE SOFTWARE (fc1)

cisco_lite Wed, 01/14/2009 - 11:55

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, media type is 10/100/1000BaseT

input flow-control is off, output flow-control is on

Clock mode is auto

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

Last input never, output 00:00:32, output hang never

Last clearing of "show interface" counters never

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 119450

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

16364141 packets input, 19262818975 bytes, 0 no buffer

Received 2669 broadcasts (2 multicasts)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

29693021342 packets output, 2671695433517 bytes, 0 underruns

0 output errors, 0 collisions, 3 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

Jon Marshall Wed, 01/14/2009 - 12:12

Okay, apologies not what i was expecting.

Please see the command reference for 12.2SX for the command "sh interface stats". Note that it only talks about process and fast switched packets not CEF switched.

Your link has made me have another search through the docs so i'll keep looking :-)

Jon

cisco_lite Wed, 01/14/2009 - 12:21

Shifting to another query..

I am experiencing giants on 'show interfaces counters errors'. The MTU set on the server is 9000 and Cat6500 interface has been enabled for 9216. I don't see any CRC or FCS errors but the giants. The application using the interface has not complained as yet. Could you please let me know why would the giants appear in such way. I thought it would always be accompanied by FCS errors.

mlund Thu, 01/15/2009 - 05:05

Hi

I'm not able to test, but I think this command could be the one.

show mls cef statistic

/Mikael

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