Keeping VoIP calls up while high IP Input process cpu time


I was having a problem with a router that I'm not sure how's the best way to prevent it from happening again. I have a MC3810 running 12.3, and it provides a PRI and NAT through a T1 data connection.

One of the computers running through the NAT got a virus and started opening up thousands of connections to port 443 per second. This caused the IP Input process to max out the CPU time, and as a side effect VoIP calls couldn't go through.

I fixed the problem with an access list so that port won't be a problem in the future, however, I'm sure at some time some other virus will cause a similar problem with another port.

Is there any way I can force the router to still handle VoIP calls even with a high CPU utilization? I know the IP Input process is obvoisly important for VoIP calls too, but I wonder if there is a way I could give higher preferences to certain types of activity over others.



Reply to
Brian McCrary
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you should configure QOS on your MC3810. QOS allowa you to priorize the VOIP over the remaining traffic.


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Reply to
Andre Janssen

QoS is the way to go to prioritize VoIP in a high traffic enviornment. On a side note though, in 12.3(14)T and later versions of IOS you can now use the "ip nat translation max-entries all-host " command to limit the number of NAT sessions on a per-host basis.This allows only X number of translations to be built per unique source ip address.

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