Bgp Scanner

Unanswered Question
Oct 20th, 2009
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Does any one have any idea on the amout of CPU a BGP scanner process will take.

I have Internet router with 3L routes and only 1 neighbor IBGP .

The router is 7513 and it take 60%.



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Overall Rating: 3.5 (2 ratings)
francisco_1 Tue, 10/20/2009 - 04:06
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depends on router bgp routing table i believe! so a router carrying a large Internet routing table bgp scanner might use more cpu. Once a minute, BGP scanner walks the BGP RIB table and performs important maintenance tasks. These tasks include checking the next-hop referenced in the router's BGP table and verifying that the next-hop devices can be reached. Thus, a large BGP table takes an equivalently large amount of time to be walked and validated.

vishwancc Tue, 10/20/2009 - 04:37
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Hi Francisco,

Thanks for the reply.

I know about what the BGP process will do.I am more intreasted to know how much and will enabling or disabling CEF have any effect on this ?



Joseph W. Doherty Tue, 10/20/2009 - 04:54
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CEF and the BGP scanner process? In interaction as far as I know.

vishwancc Tue, 10/20/2009 - 05:08
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Hi Jose,

Why i asked this is since scanner procees check the next hop reachability along with other thing,so i wanted to know how it verifies the next HOP reachabitily,as far as i know it will just check the routing table for that,but jbust wanted to make sure there is no packet sen d using CEF.



Giuseppe Larosa Tue, 10/20/2009 - 05:29
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Hello Vishwa,

you cannot disable CEF on a C7600 or GSR you could do it on a C7513 but it not recommended and it wouldn't help.

BGP scanning is the process of verifying the BGP next-hop of each prefix.

You may have a single neighbor but quite a lot of prefixes ( a full internet table is in the order of 300,000 routes nowdays)

There can be some enhancements like BGP next-hop tracking that could provide some cpu resources savings in BGP scanner.

Also consider to use a lower frequency of BGP scanning operation that would spread over time cpu usage


Hope to help


vishwancc Tue, 10/20/2009 - 05:42
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Hello Giuseppe,

Its funny i have 7513 and CEF is disabled,the reason was when i enable it my process memory is getting chocked due to this CEF,so it is disabled.

The funny part is i have Interrupt using close to 40% of 97% CPU utilization and rest 50% is BGP scan process with no CEF,but after enabling CEF it was Interrup was 35% there was not much difference.



vishwancc Tue, 10/20/2009 - 20:47
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Thanks Giuseppe,

I have already checked this link it only tells that CPU will go high due to scanning but how much there is no information , and i dont know how Cisco is expecting me to run the debug when the CPU is already running high on the core internet router.I have googled a lot but did not find antthing which give any precise vlaue or point in some direction to troubleshoot , moreover i cannot increase the scantime also from 60 sec to see some difference.




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