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Cisco 877 throughput and process

Posted on 2010-09-15
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Last Modified: 2012-05-10
Hi guys,


We have a site which recently got upgraded to a 40/40 Mbps bonded DSL connection.

The bottleneck, which I feel are two Cisco 877M's have not been upgraded to better routers. These routers currently run interface tracking and are setup for HSRP, in case the new 40/40 connection goes down we have a backup connection there.

My questions are two-fold. Firstly, would a SOHO router like 877 be able to fully utilize this 40/40 connection? The datasheet says the 877 can handle 25,000 pps. With a minimum 64 byte packet with header that translates to 16Mbps throughput. Considering that most of the interesting traffic is HTTP, FTP and as such I would assume this throughput to go up.

But our NMS shows a maximum throughput of around 20Mbps during heavy usage. Is there a reason this router cannot go higher? Or is it hardware limited.

Secondly, the router has a an average CPU usage of over 60% and frequently going over 80% usage. Is this a cause for concern at all with this router?

Thank you

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Question by:demon777
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Expert Comment

by:joseleonardo
ID: 33688239
First of all the router interface is hardware limited as the datasheet especified:

The ADSL2+ standard (ITU G.992.5) doubles the bandwidth used for downstream data transmission, effectively doubling the maximum downstream data rates, and achieving downstream data rates of up to 24 Mbps and upstream data rates of up to 1.5 Mbps.

Secondly, for the cpu utilization could be many things:

1 - have you enabled IP CEF?

2- the router is overloaded, cisco recommend to change the equipment that have CPU over 40 percent of utilization. Could you put the followigs output commands?

show proc cpu
show proc cpu history
show running-config

Regards
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by:demon777
ID: 33688574
Thanks joseleonardo, this is an Ethernet over Copper connection terminated at a NTU, it is a 40/40 connection.

ip cef is enabled, sh proc cpu output shows:


    887578943312315476767766888877753253324887867797877666552433326677577878
    529993051378957640594143320533499855152806239529976933204721842195472481
100
 90 *     *                    *           *      * *
 80 *** ***           *     ****           **** *******             ** * ***
 70 *** ***         * ****  *******        **** ********            ** *****
 60 *******       * ****************  *    ***************        **** *****
 50 ********      ******************  *    *******#********* *    **********
 40 ********    * ******************* **  ********#*#******* *  * ********##
 30 *#******** ** *******#***********************####******* **** *******###
 20 ##***************#########**##***********#########*************#***#####
 10 ####**********#################*******#################*******##########
   0....5....1....1....2....2....3....3....4....4....5....5....6....6....7..
             0    5    0    5    0    5    0    5    0    5    0    5    0
                   CPU% per hour (last 72 hours)
                  * = maximum CPU%   # = average CPU%

There is a single access list, no CBAC enabled, and the router is doing NAT.

To test the throughput for an extended time, would FTP utilize the 40/40 connection?

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Expert Comment

by:joseleonardo
ID: 33688597
The throughput never goes to take the exactly 40/40 because the encapsulation and protocol payload, since the data transfer in an FastEthernet environment is almost 13Mbits in your conexion it would be like 4Mbps.

On the other hand, Your CPU seems to be very high, please issue " show proccess cpu" without "history" in order to see what is the proccess with the higher percent.

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Author Comment

by:demon777
ID: 33688635
It seems to be all normal, with the only processes worth noting being:

75    31201069  13699448       2277  2.53%  3.62%  3.87%   0 IP Input
 4     5404659    291736      18525  0.00%  0.89%  0.82%   0 Check heaps

I was expecting around 38Mbits atleast, which I do get on burst speeds and not as a constant throughput,

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Expert Comment

by:joseleonardo
ID: 33691722
Ok, This Link Could help you with the troubleshooting with High CPU

http://www.cisco.com/en/US/products/hw/routers/ps359/products_tech_note09186a00801c2af3.shtml#ip_input

If there's not problem with bugs on your router could be that your IOS Version have a Bug.
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Expert Comment

by:joseleonardo
ID: 33701269
Hey How has you going with this issue?
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demon777 earned 0 total points
ID: 33902135
Sorry about updating this question, we replaced the router with a higher end router and achieved the rated throughput. I guess it did not have much to do with the processing.
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