03-03-2010 07:38 PM - edited 03-04-2019 07:41 AM
Hi Chaps,
A question, i have Router A connects to Router B with 2 links, 1Gbps and 100Mbps WAN circuit. Both are running OSPF. Base on cost calculation, traffic vice-versa will traverse through 1Gb link and when it fails, it goes to 100Mbps link.
Will the traffic goes back to 1Gb link when the WAN circuit recover? I have an impression that OSPF will select a path with longer uptime with more stability.. (correct me if im wrong)
Thanks
03-03-2010 07:51 PM
Hi,
When your 1GB WAN circuit recovers, type 1 LSA will be generated which will trigger a full SPF calculation. This will result in installing the best path into routing tale which obviously will be your 1 GB link.
HTH,
Nagendra
03-03-2010 08:17 PM
If the Gb links flap. The spf calculation will keep occuring. How to improve on that?
Best Regards,
Charles
03-03-2010 09:35 PM
Hi,
To avoid such a scenario and to make SPF calculation to be stablee we can use SPF Throttaling concept.
timers throttle spf spf-start spf-hold spf-max-wait
spf-start : Initial delay to schedule an SFP calculation after a change, in milliseconds. Range is from 1 to 600000.
spf-hold : Minimum hold time between two consecutive SPF calculations, in milliseconds. Range is from 1 to 600000.
spf-max-wait : Maximum wait time between two consecutive SPF calculations, in milliseconds. Range is 1 to 600000.
This example shows a router configured with the start, hold, and maximum interval values for the timers throttle spf command set at 5, 1,000, and 90,000 milliseconds, respectively.
router ospf 1
router-id 10.10.10.2
log-adjacency-changes
timers throttle spf 5 1000 90000
redistribute static subnets
network 21.21.21.0 0.0.0.255 area 0
network 22.22.22.0 0.0.0.255 area 00
for more info just go through the below URL
http://www.cisco.com/en/US/docs/ios/iproute_ospf/configuration/guide/iro_short_path_ps6441_TSD_Products_Configuration_Guide_Chapter.html
Regards
Karuppu
03-03-2010 11:05 PM
Thanks. I realize my company best practice is 50/100/5000
Best Regards,
Charles Koh
03-03-2010 11:09 PM
Hi,
Thats great.If you find the post is helpful for you,then just give rating to it.
Regards
Karuppu
03-04-2010 05:18 AM
Hello Charles,
>> I have an impression that OSPF will select a path with longer uptime with more stability.. (correct me if im wrong)
only eBGP prefers oldest path in case of a tie
this is wrong, as explained by colleagues 1GB link recover will trigger a new SPF calculation
link instability and flapping are a different question that you can deal with different tools SPF throttling, BFD and so on.
Hope to help
Giuseppe
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