Categories R&S

OSPF – Optimize convergence and scalability – LSA and SPF throttling and pacing

Those timers control how often happens SPF calculation and LSA sending.

 

Theory:

OSPF throttle timers control the interval for SPF calculation.

OSPF pacing timers control the rate at which OSPF LSA flood pacing, retransmission pacing, and group pacing updates occur.

 

Please check the following post from INE, as this is the best explanation regarding OSPF throttling and pacing http://blog.ine.com/2009/12/31/tuning-ospf-performance/  .

 

Requirements:

Tune OSPF for routers in area 0 in order to improve convergence and performance.

 

Diagram:

OSPF LSA filtering

Configuration and verification:

Let’s first check the default throttling and pacing timers:

R1#sh ip ospf 10
 Routing Process "ospf 10" with ID 11.11.11.11
SNIP
 Initial SPF schedule delay 5000 msecs
 Minimum hold time between two consecutive SPFs 10000 msecs
 Maximum wait time between two consecutive SPFs 10000 msecs
 Incremental-SPF disabled
 Minimum LSA interval 5 secs
 Minimum LSA arrival 1000 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 Number of external LSA 3. Checksum Sum 0x01830F
 Number of opaque AS LSA 0. Checksum Sum 0x000000
 Number of DCbitless external and opaque AS LSA 0
 Number of DoNotAge external and opaque AS LSA 0

 

Now we will improve the throttling timers for network convergence:

R1(config)#router ospf 10
R1(config-router)#timers throttle spf ?
    Delay between receiving a change to SPF calculation in
              milliseconds
R1(config-router)#timers throttle spf 1000 ?
    Delay between first and second SPF calculation in milliseconds
R1(config-router)#timers throttle spf 1000 2000 ?
    Maximum wait time in milliseconds for SPF calculations
R1(config-router)#timers throttle spf 1000 2000 4000

R1(config-router)#timers throttle lsa ?
    Delay to generate first occurrence of LSA in milliseconds
R1(config-router)#timers throttle lsa 2 ?
    Minimum delay between originating the same LSA in milliseconds
R1(config-router)#timers throttle lsa 2 100 ?
    Maximum delay between originating the same LSA in milliseconds
R1(config-router)#timers throttle lsa 2 100 500 

 

Let’s verify the changes:

R1#sh ip ospf 10
 Routing Process "ospf 10" with ID 11.11.11.11
 SNIP
 Initial SPF schedule delay 1000 msecs
 Minimum hold time between two consecutive SPFs 2000 msecs
 Maximum wait time between two consecutive SPFs 4000 msecs
 Incremental-SPF disabled
 Initial LSA throttle delay 2 msecs
 Minimum hold time for LSA throttle 100 msecs
 Maximum wait time for LSA throttle 500 msecs
 Minimum LSA arrival 1000 msecs

 

Now we can change the pacing timers to improve OSPF performance:

R1(config)#router ospf 10
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 ?
    The minimum interval in msec to pace limit flooding on interface
R1(config-router)#timers pacing flood 20

R1(config-router)#timers pacing lsa-group ?
    Interval in sec between group of LSA being refreshed or maxaged
R1(config-router)#timers pacing lsa-group 100

R1(config-router)#timers pacing retransmission ?
    The minimum interval in msec between neighbor retransmissions
R1(config-router)#timers pacing retransmission 30

 

And verify the changes:

R1#sh ip ospf 10
 Routing Process "ospf 10" with ID 11.11.11.11
 SNIP
 LSA group pacing timer 100 secs
 Interface flood pacing timer 20 msecs
 Retransmission pacing timer 30 msecs

 

There is no real way test this configuration in my lab.

 

I would not recommend to modify those timers anyway in production unless you really need and know what you are doing.

 

 

Thank you for reading.

 

 

OSPF – Optimize convergence and scalability – LSA and SPF throttling and pacing