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Cisco 2811 + High CPU Untilization while heavy traffic


We are having issues with our Cisco 2811 when there a lot of traffic on the device. Usually the router is down around 5%-10%. Total traffic might be around 2.0 MB. This is a router we are using at a remote campus. We do HD video conferencing every friday. We have a 10 MB internet connection that has our VPN connection to the main campus on it. While doing these VTC, the totall traffic is about 6 MB. The CPU Utilization then rises to approx 75% cause call issues and loss of sound. With another test with no one using the connection for anything else the utilization went up to 35%. The router has 128 MB Ram in it. What does anyone suggest I should look at to see if there is anything I can do to make this work better. Does the router need more RAM or do we need a larger internet pipe. Again we only have issues when we are under a heavy traffic load.


7 Replies 7


how much is your peak usage in terms of packets per second? You can get this

value and compare it to this figures:

Beside, if you have multicast traffic you could experience higher cpu usage since that

might be process switched.

Kind regards


Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), Version 12.4(22)T, RELEASE SOFTWARE (fc1)
Technical Support:
Copyright (c) 1986-2008 by Cisco Systems, Inc.
Compiled Fri 10-Oct-08 00:05 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

WB-2811-Voice uptime is 10 weeks, 1 day, 22 hours, 18 minutes
System returned to ROM by reload at 17:11:18 EDT Tue Aug 14 2012
System restarted at 17:13:46 EDT Tue Aug 14 2012
System image file is "flash:c2800nm-advipservicesk9-mz.124-22.T.bin"

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Cisco 2811 (revision 53.51) with 239616K/22528K bytes of memory.
Processor board ID FTX1248A20Y
3 FastEthernet interfaces
1 terminal line
1 Channelized (E1 or T1)/PRI port
1 Virtual Private Network (VPN) Module
4 Voice FXO interfaces
1 cisco Integrated Service Engine(s)
   CCA NME-NAC-K9 4.9.0 in slot 1
DRAM configuration is 64 bits wide with parity enabled.
239K bytes of non-volatile configuration memory.
125440K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102


Only about 2000 pkts/sec when the issue is going on.

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"VPN"?  High CPU loading might be due to IP fragmentation of video packets.

The call and sound quality issues might be related to transient congestion if you're not using QoS to manage your bandwidth or you share WAN bandwidth with multiple VPN tunnels and/or "native" Internet traffic.

WB-2811-Voice#show interface summary

*: interface is up
IHQ: pkts in input hold queue     IQD: pkts dropped from input queue
OHQ: pkts in output hold queue    OQD: pkts dropped from output queue
RXBS: rx rate (bits/sec)          RXPS: rx rate (pkts/sec)
TXBS: tx rate (bits/sec)          TXPS: tx rate (pkts/sec)
TRTL: throttle count

  Interface              IHQ   IQD  OHQ   OQD  RXBS RXPS  TXBS TXPS TRTL
  FastEthernet0/0          0     0    0     0     0    0     0    0    0
* FastEthernet0/1          0    52    0     0 565000  135 1259000  160    1
* FastEthernet0/1.600      -     -    -     -     -    -     -    -   -
* FastEthernet0/1.601      -     -    -     -     -    -     -    -   -
* FastEthernet0/1.602      -     -    -     -     -    -     -    -   -
* FastEthernet0/1.2884     -     -    -     -     -    -     -    -   -
* FastEthernet0/1/0        0     0    0    16 189000   11     0    0    0
* In1/0                    0     0    0     0  2000    1  3000    2    5
  NVI0                     0     0    0     0     0    0     0    0    0
* SSLVPN-VIF0              0     0    0     0     0    0     0    0    0
* Tunnel0                  0     0    0 142610     0    0     0    0    0
NOTE:No separate counters are maintained for subinterfaces
     Hence Details of subinterface are not shown


     Inisitially it was sharing the bandwidth with the VPN Tunnel and "Native" Internet Traffic. I moved it over to our WAN connection. Our ISP basically gives us a VLAN to route traffic to our campuses, however... Phones, Printing, File Servers, and VTC traffic all move over that link also. "Native" Internet traffic goes out a separate port. Hoever it is only a 5MB Link.        

  Interface              IHQ   IQD  OHQ   OQD  RXBS RXPS  TXBS TXPS TRTL


  FastEthernet0/0          0     0    0     0     0    0     0    0    0

* FastEthernet0/1          0    52    0     0 4568000  848 5815000  907    1

This is an example of what I get for this port with Show interfaces summary. The TXBS is over the 5MB.
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