OSPF Flapping

[mazlan.alatif]

I have problem with my OSPF network. It seems that my OPSF network is not stable. It keep refreshing even there is no convergence/changing in our network. This happen let say after 2,3 minutes, but sometimes within 1 hour. Is also affected our static routes that we distributes to OSPF (E2). Why my E2 also affected?

[Harold Ritter]

Could you please elaborate on what you mean when you say that the E2 are affected.

Could you please do a "sh ip ospf stat" to see the frequency at which the spf is performed and the reason for the spf run.

Hope this helps,

[mazlan.alatif]

Hi, when i turn on debug ip ospf monitor, there is a meesage that keep appears and i realize that everytime this msgs appears my ospf will refresh. Maybe you could help me to translate this msg: What is the cause what why 0.0.0.0 ?

Jun 27 14:57:41.802: OSPF: Schedule SPF in area 0

Change in LS ID 0.0.0.0, LSA type X

Jun 27 14:57:42.002: OSPF: reset throttling to 5000ms

Jun 27 14:57:42.002: OSPF: schedule SPF: spf_time 16w3d wait_interval 5000msBKJ94-RTBH#

Jun 27 14:57:47.019: OSPF: Begin SPF at 9945778.880ms, process time 35350504ms

Jun 27 14:57:47.019: spf_time 16w3d, wait_interval 5000ms

Jun 27 14:57:47.207: OSPF: wait_interval 10000ms next wait_interval 10000ms

Jun 27 14:57:47.207: OSPF: End SPF at 9945779.068ms, Total elapsed time 188ms

Jun 27 14:57:47.207: Schedule time 16w3d, Next wait_interval 10000ms

Jun 27 14:57:47.207: Intra: 0ms, Inter: 0ms, External: 188ms

Jun 27 14:57:47.207: R: 0, N: 0, Stubs: 0

Jun 27 14:57:47.207: SN: 0, SA: 0, X5: 2316, X7: 0

Jun 27 14:57:47.207: SPF suspends: 0 intra, 0 total

[Harold Ritter]

It seems like the default route is the one causing the issue, at least in this particular case. Keep monitoring for a while and see if the default route is always the cause of the SPF recalculation. If so, verify why the default route keeps changing.

Hope this helps,

[mazlan.alatif]

Hi, I have monitor this for 2 hour and it keep appears after 2,3 minutes. I am not sure why the default route keep changing. When i show ip ospf database external, teh default route is advertised by 2 of my routers. I am not sure why this happen? and the msg appears on the advertised router is :

Jun 24 14:18:11.822: OSPF: reset throttling to 0ms

Jun 24 14:18:17.502: OSPF: reset throttling to 0ms

Jun 24 14:18:23.862: OSPF: reset throttling to 0ms

SPF recalculation happen quite regularly, and it effect our perfomance. May i know what can cause SPF recalculation other than network conergence? And why this defaut route keep changing.

[Harold Ritter]

start with the routers where the default routes are originated and see if the default gateway on these two routers are stable.

Any changes in the network can cause SPF calculation.

Hope this helps,

[mazlan.alatif]

Hi, I have monitor the gateway and it is stable, no down or anything. But i found this config in my ospf. Maybe this is the cause?

router ospf 1

default-information originate

What is the use of this cmd actly? What if i remove this cmd and what will be the impact?

[Harold Ritter]

Mazlan,

This command is actually what causes this router to generate the default route as an external LSA. Removing it would cause the default route to go away. This command requires a default route from a source other than OSPF to already be in the RIB. What is the source of the default route on this router? Can you provide us with a "show ip route 0.0.0.0" taken from this router. It would also be useful if you could post the entire ospf configuration from that same router.

Thanks,

[mazlan.alatif]

Hi Hritter,

Thank you for the explaination.

Below is the output of sh ip route 0.0.0.0 and the entire ospf config as requested:

#sh ip route 0.0.0.0

Routing entry for 0.0.0.0/0, supernet

Known via "static", distance 1, metric 0 (connected), candidate default path

Redistributing via ospf 1

Routing Descriptor Blocks:

* directly connected, via POS0/0/0

Route metric is 0, traffic share count is 1

#sh run | b ospf 1

router ospf 1

log-adjacency-changes

redistribute static subnets

passive-interface POS0/0/0

passive-interface Serial1/0/0

passive-interface Serial1/0/1

passive-interface Serial1/1/0:0

network 61.6.17.32 0.0.0.3 area 0

network 61.6.21.8 0.0.0.3 area 0

network 61.6.21.12 0.0.0.3 area 0

network 61.6.191.14 0.0.0.0 area 0

network 66.110.10.8 0.0.0.3 area 0

network 216.168.170.0 0.0.0.3 area 0

default-information originate

[Harold Ritter]

This configuration looks fine. What about the other router that is also injecting the default route. Could you please provide the same info for this other router.

Thanks,

[Harold Ritter]

The best way to get additional info about why the SPF is ran every 2 to 3 minutes would be to use "deb ip ospf spf" and see precisely what changes in the LSA cause the SPF to be executed.

Thanks,

[Harold Ritter]

You might want to run "deb ip ospf spf external" just to be safe.

Thanks,

[mazlan.alatif]

Hi Hritter, below is the config at my other router. I will post you all debug output aftger this:

Thank you in advanced

#sh ip route 0.0.0.0

Routing entry for 0.0.0.0/0, supernet

Known via "static", distance 1, metric 0 (connected), candidate default path

Redistributing via ospf 1

Routing Descriptor Blocks:

* directly connected, via POS0/0/0

Route metric is 0, traffic share count is 1

#sh run | b ospf 1

router ospf 1

log-adjacency-changes

redistribute static subnets

passive-interface POS0/0/0

network 61.6.2.48 0.0.0.3 area 0

network 61.6.21.8 0.0.0.3 area 0

network 61.6.191.15 0.0.0.0 area 0

network 64.86.173.136 0.0.0.3 area 0

default-information originate

[mazlan.alatif]

Hritter,

Below is the output of debug ip ospf external: Here i can attached only half of it, because it is too long:

Jun 29 15:01:42.046: Add better path to LSA ID 202.186.25.160, gateway 61.6.162.11, dist 20

Jun 29 15:01:42.046: Add path: next-hop 61.6.162.11, interface GigabitEthernet0/3

Jun 29 15:01:42.046: Add path: next-hop 61.6.162.90, interface GigabitEthernet0/3

Jun 29 15:01:42.046: Add path: next-hop 61.6.162.4, interface GigabitEthernet0/3

Jun 29 15:01:42.046: Add path: next-hop 61.6.162.3, interface GigabitEthernet0/3

Jun 29 15:01:42.046: OSPF: delete lsa id 202.186.25.160, type 5, adv rtr 61.6.191.59 from delete list

Jun 29 15:01:42.046: network update dest_addr 202.186.25.160 mask 255.255.255.240 gateway 61.6.162.3

Jun 29 15:01:42.046: Add External Route to 202.186.25.160. Metric: 20, Next Hop: 61.6.162.3

Jun 29 15:01:42.046: network update dest_addr 202.186.25.160 mask 255.255.255.240 gateway 61.6.162.4

Jun 29 15:01:42.046: Add External Route to 202.186.25.160. Metric: 20, Next Hop: 61.6.162.4

Jun 29 15:01:42.046: network update dest_addr 202.186.25.160 mask 255.255.255.240 gateway 61.6.162.90

[Harold Ritter]

Mazlan,

In this specific example, it is not the default route causing the SPF. Could you please send me the whole log to my email address hritter@cisco.com. Also send me the output of "show ip ospf stat"

Thanks,