GRE Tunnel Problem

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Apr 13th, 2008
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Hi, we have GRE tunnel with EIGRP running between HK and India office. Sometimes, the response of some services through the GRE tunnel is very slow. At that moment, when we ping the GRE tunnel IP, there is serious delay, however, there is no problem in pining the router real IP.

There is netflow configured in the routers. And I noticed the CPU utilization is a bit high. Here is the "show proc cpu" from two routers:

CPU utilization for five seconds: 99%/8%; one minute: 46%; five minutes: 35%

CPU utilization for five seconds: 75%/21%; one minute: 40%; five minutes: 30%

Is that a cause for this problem?

Any other possible reasons?


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royalblues Mon, 04/14/2008 - 01:05
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There should be much of a difference in the delay for the tunnel ip and the real IP.

CPU utilization of 99% is very high. it will certainly lead to slowness in applications as well as increase the delay

Check for the processes that is consuming more CPU. Sometimes it could be just due to a bug in the IOS


frances.lau Mon, 04/14/2008 - 19:13
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I have checked the processes that is comsuming the CPU is "SSH", but i found there is only only two SSH sessions. Besides, IOS has been checked as well, and there is no related bug for it.

shiva_ial Mon, 04/14/2008 - 04:31
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hi frances,

your tunnel end router may defragment the packets which is fragmented when tunnel getting created so check whether any fragmentation is eating up your router cpu ?

rgds /shiva

frances.lau Mon, 04/14/2008 - 19:08
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hi shiva,

how to check if the fragmentation is eating up the router cpu?



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