HIGH CPU UTILISATION ON GGSN

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Apr 6th, 2010
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please am having high cpu utilisation of over 80% on my GGSN cisco 7600 vxr and 7200.am doing GPRS-GTP on the software loopback interface.please how do i manage this issue.


thanks alot

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Giuseppe Larosa Tue, 04/06/2010 - 12:57
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Hello Olankule,


take sh proc cpu sorted


sh proc cpu sorted 1min


from affected devices in order to understand what processes use more resources and how much cpu is used by SW interrupts


To be noted this could be caused by  an increase in traffic volume and number of GTP sessions


Hope to help

Giuseppe

olakunle06 Wed, 04/07/2010 - 00:51
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thanks for the help.


after issuing the command i noted IP INPUT process consuming most memory.so how can i sove the problem.thanks for anticipated response

Giuseppe Larosa Wed, 04/07/2010 - 01:41
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Hello Olankule,


so IP input uses a lot of cpu resources this probably means that the router is process switching a lot of packets.


Can this increase in cpu usage be caused simply by an increase in traffic?


can you compare current traffic levels on router interfaces with that of previuos time periods?


What was the cpu usage before?

My guess is it could be relatively high also before because to encapsulate IP packets into GTP tunnels is cpu intensive.


Have you performed any configuration change or change of IOS image recently?


Examing sh log on router do you see any message related to cpu usage or to cpu processes taking too much cpu time?


Hope to help

Giuseppe

Giuseppe Larosa Wed, 04/07/2010 - 06:21
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Hello Olankule,

first of all sorry for the basic note:

but you don'have debug ip pack detail all the time I hope otherwise this can cause the issue you see (debug causes very high cpu usage)


looking at the debug lines I see that there are some fragmented GTP packets


-More--         Apr  3 21:58:00.282: IP: s=10.105.5.41 (FastEthernet1/1), d=41.203.65.114, len 76, rcvd 4
--More--         Apr  3 21:58:00.282:     UDP src=2152, dst=2152
--More--         Apr  3 21:58:00.282: IP: tableid=0, s=41.203.64.44 (FastEthernet1/1), d=41.203.65.114 (Loopback6), routed via RIB
--More--         Apr  3 21:58:00.282: IP: s=41.203.64.44 (FastEthernet1/1), d=41.203.65.114, len 88, rcvd 4
--More--         Apr  3 21:58:00.282:     UDP src=10651, dst=2152
--More--         Apr  3 21:58:00.282: IP: tableid=0, s=41.203.65.97 (FastEthernet1/0), d=41.203.65.114 (Loopback6), routed via RIB
--More--         Apr  3 21:58:00.282: IP: s=41.203.65.97 (FastEthernet1/0), d=41.203.65.114, len 1500, rcvd 4
--More--         Apr  3 21:58:00.282:     IP Fragment, Ident = 1910, fragment offset = 0
--More--         Apr  3 21:58:00.282:     UDP src=10651, dst=2152


this can cause an increase of cpu usage, original packets can be of normal size but then there is the GTP overhead and  this leads to the need of fragmentation


Note:

My is only a guess that GTP can cause high cpu usage based on the fact that packets needs to be inspected deeply to be placed in the correct session within the GTP tunnel it is wise to open a TAC SR if this is impacting or it is going to impact service


Hope to help

Giuseppe

olakunle06 Wed, 04/07/2010 - 06:35
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THANKS FOR KIND SUPPORT AND EXPLANATION. WOULD CONTACT TAC ASP.

I must really appreciate your contributions on this forum,your responses are very useful

and precise.

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