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New Member

BGP - RIB updates / High CPU

Greetings All,

I have any issue wherein I'm having difficulty pinpointing the problem because from a birds eye view everything looks ok.

First, I have the following setup:

(internet) <> [ISP-A] <ebgp> [rtr1] <ibgp> [rtr2] <ebgp> [ISP-B] (internet)

NOTE: only getting partial routes with default from both ISP's

At first glance everything looks fine, because BGP sessions are stable. However, I noticed that the CPU or RTR2 was spiking every minute. Looking into it showed that the CPU spikes are caused by BGP/RIB updates. I am 80% sure that the updates originating from ISPA. The question is how do i verify this? and how do i lessen the impact of those updates.

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

Re: BGP - RIB updates / High CPU

Hi,

If the next-hop is known via BGP this can cause such issues with the BGP scanner timer.You have to make sure that all the BGP next hops are known by the IGP. Try configuring "next-hop-self" on the iBGP peering. Another solution is to make the iBGP AD higher than the IGP AD, making sure that the next hope is known via the IGP instead of iBGP.

HTH

Joe.

8 REPLIES
New Member

Re: BGP - RIB updates / High CPU

Few more questions. Is there a best practice incoming BGP update filter that anyone uses for Internet Edge routers?

Re: BGP - RIB updates / High CPU

Hi,

Need some more inputs from your RTR2 .

1- sh process cpu | exc 0.00

2- Your router memory

3- your BGP config from both router.

4- confirm if any path-mtu discovery configured  (or provide output of show ip bgp neighbors | include max data ).

5-

meanwhile if you can push only default route from Rtr1 to Rtr2 and see any improvement in cpu usage, also confirm have you changed default scantime

Regards

Mahesh

New Member

Re: BGP - RIB updates / High CPU

Hi,

As you had mentions in your post, if your network set up is having two different router connected to different isp and if you are running IBGP peer between your two routers. chances are there where your AS will act as the transit AS.

(internet) <> [ISP-A] [rtr1] [rtr2] [ISP-B] (internet)

you should make sure that routes learned via isp A should not advertised to ISP B. by default it will happen because you are running IBGP peer between your routers.

1. let us know your bgp configuration on two router

2. let us know how many routes your learning from each isp and how many is being advertised to each isp.

Regards,

Hariharan k

New Member

Re: BGP - RIB updates / High CPU

Hi Hariharan,

We have outbound BGP filters that only allows our prefix to be advertised to the ISP's. So we are not a transit network.

New Member

Re: BGP - RIB updates / High CPU

This is the output when the CPU spikes

CPU utilization for five seconds: 86%/0%; one minute: 40%; five minutes: 32%
PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
   6       29604      1583      18701  0.47%  0.41%  0.43%   0 Check heaps
  43        5824      6017        967  0.15%  0.10%  0.10%   0 Per-Second Jobs

160      799624      4303     185829 57.03% 20.20% 15.48%   0 IP RIB Update
163      160404      8217      19520 10.55%  3.23%  2.84%   0 XDR mcast
237      372096      4814      77294 13.43%  9.71%  7.47%   0 BGP Router
241      197864      1184     167114  4.23%  5.22%  4.06%   0 BGP Event

Memory 512Mb - using only 159Mb

show ip bgp summary
BGP router identifier x.x.x.x, local AS number xxxx
BGP table version is 12723897, main routing table version 12723897
132615 network entries using 16046415 bytes of memory
246291 path entries using 12807132 bytes of memory
24216/14485 BGP path/bestpath attribute entries using 3390240 bytes of memory
21091 BGP AS-PATH entries using 573986 bytes of memory
1 BGP community entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 32817797 total bytes of memory
89911 received paths for inbound soft reconfiguration
BGP activity 133809/1191 prefixes, 249017/2726 paths, scan interval 60 secs

Both configs are identical.

router bgp 1231
no synchronization
bgp log-neighbor-changes
redistribute eigrp 1 route-map ROUTEMAPNAME
neighbor x.x.x.x remote-as 1231 (iBGP)
neighbor x.x.x.x update-source Loopback1
neighbor x.x.x.x version 4
neighbor x.x.x.x soft-reconfiguration inbound
neighbor 1.1.1.1 remote-as 4567 (eBGP
neighbor  1.1.1.1 version 4
neighbor  1.1.1.1 timers 30 90
neighbor  1.1.1.1 send-community
neighbor  1.1.1.1 soft-reconfiguration inbound
neighbor  1.1.1.1 weight 1000
neighbor  1.1.1.1 prefix-list Filter-out out
no auto-summary

show ip bgp neighbors | inc max data
Datagrams (max data segment is 1440 bytes):
Datagrams (max data segment is 4410 bytes):

Re: BGP - RIB updates / High CPU

Hi,

BGP config and parameter seems to be ok . your main concern is ip rib update process which is caused by routes yet not installed in

RIB (i mean waiting to be processed by cpu).

can you confirm if ip cef is configured in this router. If not can you go for it.

Regards

Mahesh

New Member

Re: BGP - RIB updates / High CPU

Hi,

If the next-hop is known via BGP this can cause such issues with the BGP scanner timer.You have to make sure that all the BGP next hops are known by the IGP. Try configuring "next-hop-self" on the iBGP peering. Another solution is to make the iBGP AD higher than the IGP AD, making sure that the next hope is known via the IGP instead of iBGP.

HTH

Joe.

New Member

Re: BGP - RIB updates / High CPU

I had a call with TAC this is what caused the issue. Thanks for the response

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