OSPF LSA Throttling

Lessons Discussion
22

Hi,

Aside from the LSA throttling, I see there is also the flood pacing timer. How does it affect throttling? Could it delay flooding if other LSAs need sending first?

Also, just to clarify, if multiple instances of the same LSA are generated during the start/hold time, when it comes to flooding only the LSA that was most recently generated is used, not all of them, correct?

Regards,

Sam

23

Hello Samir

Where OSPF LSA throttling timers adjust the delay of the generation of LSAs during network instability, the pacing timers are used to adjust the rate at which OSPF LSA flood pacing, retransmission pacing, and group pacing updates occur. You can see these options in the following CLI context sensitive help:

R1(config-router)#timers pacing ?
  flood           OSPF flood pacing timer
  lsa-group       OSPF LSA group pacing timer
  retransmission  OSPF retransmission pacing timer

R1(config-router)#timers pacing
  • Flood pacing - Configuring OSPF flood pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF transmission queue. (Default 33 milliseconds)
  • Retransmission pacing - Configuring OSPF retransmission pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF retransmission queue. (Default 240 seconds)
  • Group pacing - Cisco IOS software groups the periodic refresh of LSAs to improve the LSA packing density for the refreshes in large topologies. The group timer controls the interval used for group LSA refreshment; however, this timer does not change the frequency that individual LSAs are refreshed which is every 30 minutes. (Default 66 milliseconds)

As stated in Cisco Documentation:

The default settings for OSPF packet pacing timers are suitable for the majority of OSPF deployments. You should change the default timers only as a last resort.

The Cisco command reference for these commands can be found at the following links:

I hope this has been helpful!

Laz