[c-nsp] packet drop due ti CAR (rate-limit)

[Oliver Boehmer (oboehmer)]

Muhammad Farooq <mailto:scorpianbiz at hotmail.com> wrote on Monday,
October 13, 2008 12:09 PM:

> We have 24 subinterfaces on this Fastethernet link and we are facing
> problem on all sub interfaces. We have other gigi interfaces on this
> router on which we are using dot1q but they are running perfectly.
> Please find below show rate-limit output for one of problematic
> interfaces.    
> 
> FastEthernet3/0.8 Alfalah GHP
>   Input
>     matches: all traffic
>       params:  512000 bps, 48000 limit, 96000 extended limit
>       conformed 31000 packets, 23768856 bytes; action: transmit
>       exceeded 310 packets, 287635 bytes; action: drop
>       last packet: 32ms ago, current burst: 34513 bytes
>       last cleared 00:06:55 ago, conformed 457000 bps, exceeded 5000
>   bps Output
>     matches: all traffic
>       params:  512000 bps, 48000 limit, 96000 extended limit
>       conformed 24550 packets, 14268239 bytes; action: transmit
>       exceeded 3 packets, 354 bytes; action: drop
>       last packet: 44ms ago, current burst: 58 bytes
>       last cleared 00:06:55 ago, conformed 274000 bps, exceeded 0 bps

Well, CAR drops traffic, which counts up in the interface output drops..
The first interface drops 1% of the traffic as excess traffic, the
overall drop rate (from the initial "show int") is in the range of 0.2%,
so I would consider this "expected" behaviour due to traffic bursts
which are rate-limited by CAR..

	oli


> 
> ----------------------------------------
>> Subject: RE: [c-nsp] packet drop due ti CAR (rate-limit)
>> Date: Mon, 13 Oct 2008 10:08:53 +0200
>> From: oboehmer at cisco.com
>> To: scorpianbiz at hotmail.com; cisco-nsp at puck.nether.net
>> 
>> Muhammad Farooq <> wrote on Monday, October 13, 2008 9:37 AM:
>> 
>>> Hi,
>>> 
>>> we are having packet drops issue due to rate limit on fastethernet
>>> of 3845 router. We are using dot1q on that interface. If we remove
>>> rate-limit then packet drop issue solves. Please note that with
>>> increase in rate limit packet drop interval also increases and it
>>> make a pattern. Output of show interface is pasted below. Running
>>> IOS of router is c3845-advipservicesk9-mz.123-14.T7.bin and
>>> interface utilization is not more that 35%
>>> 
>>> interface FastEthernet3/0
>>> no ip address
>>> load-interval 30
>>> duplex full
>>> speed 100
>> 
>> can you show some iterations of "show int rate-limit" (best after
>> "clear counter") Please bear in mind that TCP traffic can be very
>> bursty and CAR/rate-limit can drop these bursts..
>> 
>> 	oli
>> 
> 
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