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New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi all,

I  have OSPF running on 2691 Router and it has 2 interfaces that connect to each 3550 switch.

2691Router#$                                                sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.30.2      1   FULL/BDR        00:00:35    192.168.6.2     FastEthernet1/0
3.3.3.3           1   FULL/BDR        00:00:35    192.168.5.2     FastEthernet0/1


2691Router#  sh ip ospf  int
FastEthernet1/0 is up, line protocol is up
  Internet Address 192.168.6.3/31, Area 0
  Process ID 1, Router ID 192.168.6.3, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 192.168.6.3, Interface address 192.168.6.3
  Backup Designated router (ID) 192.168.30.2, Interface address 192.168.6.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:04
  Supports Link-local Signaling (LLS)
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 3
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 192.168.30.2  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)


FastEthernet0/1 is up, line protocol is up
  Internet Address 192.168.5.3/31, Area 0
  Process ID 1, Router ID 192.168.6.3, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 192.168.6.3, Interface address 192.168.5.3
  Backup Designated router (ID) 3.3.3.3, Interface address 192.168.5.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:09
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 4
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 3.3.3.3  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)
2691Router#

2691Router#sh ip int brief

Interface                  IP-Address      OK? Method Status                Protocol

FastEthernet0/0            70.71.73.110    YES DHCP   up                    up

FastEthernet0/1            192.168.5.3     YES NVRAM  up                    up

FastEthernet1/0            192.168.6.3     YES NVRAM  up                    up

Here in  this case interface fa1/0 is DR  to both the 3550 Switches.

When i have 2 PC runnning on LAN  and are accessing the internet then

sh pro cpu on 2691 Router touches 99%

       5           1                       9   9

    57892532212225804442656649532222222222295544

100                                        *

90                                        *   *

80                                        *   *

70                                        *   *

60    *                                   *   *

50    *                                   *   *

40    *                                   *   *

30    *                                   *   *

20    *                                   *   *

10 **** *       ***    **** **            *** *

   0....5....1....1....2....2....3....3....4....4....5....5....6....6....7..

             0    5    0    5    0    5    0    5    0    5    0    5    0

What should i do to fix the high cpu utilization on Router?

i read that

The usage of ip ospf priority is recommended to avoid to have the same router acting as DR

in multiple LAN segments that will increase its CPU load.

Should i make the 2691 Router as DR  for int fa0/1  and make 3550 switch DR  for interface connecting to the router?

Many thanks

MAhesh

13 REPLIES
New Member

Re: OSPF DR Router on two Lan segments causes high CPU load

Are you running secondary addresses on your Eth ports? You say that you have PCs on the LAN segments yet it shows a 31 bit mask?

Sent from Cisco Technical Support iPad App

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi Craig,

each 3550 switch is running HSRP.

gateway of pc is 192.168.20.3  HSRP  active.

Router and Switch are connected by /31 address

Thanks

OSPF DR Router on two Lan segments causes high CPU load

Hi Mahesh,

How can you be so sure that the 99% spike is caused by the ospf protocol? I mean did  you check sh proc cpu sorted and see its actually ospf causing this issue or anyother wireshark or something that could show this. You are right when you say that to be a DR the HW should have better specs etc.but if its only for a bunch of LSA's I dont think it should be a big issue ( I am assuming your network is not that large) to have the router DR for two LAN segments.

when your users connect to the internet how much BW are they using? Remember its also about the throughput of the router that culd cause CPU spiking. A ciso 2691 can handle upto 35.84Mbps of CEF switching. This also includes the traffic between the interfaces as well and not just internet..

Hope this gives some indicators

Regards

Kishore

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi Kishore

Thanks for reply.

when i do sh process cpu what should i look for that would indicate that OSPF protocol is causing spike?

This step is for my home Network.where 2691 connects to the Cable modem.

How can i check throughput on the router?

Thanks

MAhesh

OSPF DR Router on two Lan segments causes high CPU load

Hi mahesh,

check the interface traffic going across both the interfaces. also change the load interval on the interfaces to 30 seconds which will give u a good indicaion of how much traffic is going acrosss..

Also, when you do sho proc cpu sorted | ex 0.00% do you see lot of interrupts? if yes then below link should help you

http://www.cisco.com/en/US/products/hw/routers/ps359/products_tech_note09186a00801c2af0.shtml

if you are fully assured that the high CPU is caused by ospf then please look at the lnk below and see if that helps

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t4/feature/guide/ftospfct.html

Regards,

Kishore

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi,

Thanks for reply

here is output

2691Router#$                               sho proc cpu sorted | ex 0.00%

CPU utilization for five seconds: 2%/1%; one minute: 1%; five minutes: 0%

PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process

  81        5232     22710        230  0.81%  0.38%  0.12%  67 Virtual Exec

  17      374284   4172540         89  0.16%  0.15%  0.16%   0 ARP Input

  61        5348     20231        264  0.08%  0.06%  0.02%  66 Virtual Exec

129          88   1715848          0  0.08%  0.04%  0.06%   0 RBSCP Background

  77       31228    157208        198  0.08%  0.07%  0.02%   0 IP Input


which interrupts i should look for?

VIP Super Bronze

OSPF DR Router on two Lan segments causes high CPU load

Hi Mahesh,

Theses numbers are ok.  The CPU utilization is only at 1 or 2% which is good. Is OSPF enabled with these numbers?

HTH

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi Reza,

Thanks for reply.

Yes ospf is enabled right now.

VIP Super Bronze

OSPF DR Router on two Lan segments causes high CPU load

Mahesh,

These numbers are good.  Try sho proc cpu sorted every 5 a few times during busy times, if they are still the same then I don't see an issue.

HTH

Reza

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi Reza,

Thanks for reply i will try that and will let you know.

Mahesh

Bronze

OSPF DR Router on two Lan segments causes high CPU load

Hi Mahesh,

Why are you using /31 bit mask ??

what is the exact design plan of your setup ??

I never used /31 and dont know much about it, can you try changing the ip subnets to /30 or /24 and see some changes ???

New Member

Re: OSPF DR Router on two Lan segments causes high CPU load

Yes that confused me as well. Only ever seen /31 on serial pt links never on an Ethernet. I think you need a diagram to see the infrastructure..

Sent from Cisco Technical Support iPad App

New Member

OSPF DR Router on two Lan segments causes high CPU load

Hi.

Thanks for reply.

/31  does not cause any issues.

I have question about choosing DR  or BDR  in OSPF.

I have 2 3550 switches running HSRP  and they both connect to WAN  router.

Right now Active HSRP  switch 3550 A   is DR  for all the vlans.

Standy HSRP switch 3550 B  is BDR  for the all the vlans

WAN  router is DR   for both the interfaces that connect to each 3550 switch.

Is this topology ok  fo DR and BDR?

thanks

mahesh

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