4

Is there a Cisco command that would allow one to modify the default value of 1800 seconds (30 min) for the OSPF LSA refresh rate?

  • I have been building OSPF networks for over a decade, including sites with a hundred routers in area zero alone... I never found a need to adjust this timer... how did you conclude that changing this is either required or a good idea? – Mike Pennington Jun 1 '13 at 7:17
  • We are planning to execute a test that requires increased speed in the convergence process and I was thinking to force this by shortening the LSA refresh rate. – THE DOCTOR Jun 3 '13 at 21:42
9

You cannot change the LSRefreshTime because it's hard-coded as an "architectural constant" in the OSPF RFC.

1
timers lsa-group-pacing

From OSPF commands, (IOS 12 is linked)

I'm suspicious that the default (in that doc) is 240 though, maybe this isn't the right knob... :/


Doesn't seem you can change individually, from the CF Guide...

This problem is solved by configuring each LSA to have its own timer. To again use the example of refreshing, each LSA gets refreshed when it is 30 minutes old, independent of other LSAs. So the CPU is used only when necessary. However, LSAs being refreshed at frequent, random intervals would require many packets for the few refreshed LSAs the router must send out, which would be inefficient use of bandwidth.

Therefore, the router delays the LSA refresh function for an interval of time instead of performing it when the individual timers are reached. The accumulated LSAs constitute a group, which is then refreshed and sent out in one packet or more. Thus, the refresh packets are paced, as are the checksumming and aging. The pacing interval is configurable; it defaults to 4 minutes, which is randomized to further avoid synchronization.

  • 3
    It's not, pacing impacts the distribution and spreading of LSAs expiring at a similar time. Setting it to 240 means that LSAs expiring within 240 seconds of each other will be grouped together and spread out. The documentation often references the "default" of expiry being 1 hour but I've found no commands to adjust the expiry or the refresh. – Mark May 31 '13 at 17:46
  • ...and I now see others have the same Q: learningnetwork.cisco.com/thread/29872 – Craig Constantine May 31 '13 at 17:49
  • Doesn't seem you can change individually... editing above because of comment lenght restrictions. Hopefully someone else will swoop in and give you a definitive A. – Craig Constantine May 31 '13 at 17:56

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