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Processor-switched forwarding causes router to drop packets - debug?

Unanswered Question

We found that one of our 7200 series router drops some packets (at least ICMP-Type) if we do NOT use ip cef on the interfaces. The processor utilization without ip cef is about 25%, so we would not expect this behaviour. Knowing that enabling ip cef fixes this, but we are looking for the command to SEE that there are packets droped and how much packets are affected. Does anybody have an idea here?

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didyap Fri, 10/10/2003 - 06:45
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The show interfaces [type number] stats provides information regarding the number of packets that are process-switched, fast-switched (any fast switching path), and distributed-switched (for VIP capable platforms). This is a hidden command.

show interfaces [type number] switching command shows the number of sent and received packets on an interface, classified per switching path. This is a hidden command.

You may also use the show interfaces command to see the number of drops.

Use the debug ip packet command if you want debug information.

rlcarr Fri, 10/17/2003 - 07:51
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Using just your plain 'show interface' command you will be able to see drops. But you mention that the counter doesn't increase. Where are you determining that you are really dropping packets?


Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 4

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 321000 bits/sec, 50 packets/sec

5 minute output rate 212000 bits/sec, 82 packets/sec


Also, you can change your 'load-interval' on the interface to view the input/output rates for levels smaller than the '5 minute' default.

You didn't mention which NPE you have but here are some stats from the Cisco Web in regards to packets per second.

NPE Process CEF

100 7,000 100,000

200 13,000 200,000

300 20,000 353,000

400 20,000 420,000

Hope this helps,



We did constant pings(ICMP) over the router and realized that sometimes some replies didn´t arrive.

We saw the problem also, when we did a ping from a neighbouring router to the 7200-router itself...

We use 100MBit-full mode and a 3548CISCO-Switch, and the overall-utilization was lower than 20 MBit.....

With CEF, of course, everything is working....

IOS is 12.3.1


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