-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Petr
Lapukhov
Sent: Saturday, May 22, 2010 9:08 PM
To: Hussam EL Kebbi
Cc: joe_astorino_at_comcast.net; ccielab_at_groupstudy.com
Subject: Re: OSPF Performance
Hi,
In general, throttling timers should be tuned according to your goals.
Often, the primary goal is fast network convergence. In this case, you
should be mainly concerned with the *initial* delays for LSA/SPF throttling
timers, in addition to tuning timers related to link failure detection. The
initial delay for SPF run should be small enough to allow fast response but
long enough to allow LSA flooding before the SPF run, as OSPF has no special
knob (yet) to ensure fast LSA flooding, like ISIS has. As for other timers,
the interval between consecutive SPF runs should be no less than the time it
takes to run full SPF (from the output of "show ip ospf statistics" or "show
isis spf-log"). You may further space this delay to reduce CPU load for
unstable networks, e.g. if the max-wait=2xSPF_Runtime then your SPF
calculation will not take more than 50% of CPU at any moment. For LSA
throttling, the maximum delay should be no less than the time it takes
network to fully converge (progation delay + spf delay + RIB/FIB update
delay). However, finding these values accurately could be a problem (e.g.
it's hard to find RIB/FIB update delays for all platforms), so normally all
timers are found empirically. Per Cisco's experimentally validated design:
https://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/routed-ex.html
You may start by setting LSA/SPF throttling timers to 10 100 5000
milliseconds (start/hold/max). This configuration results in subsecond
convergence after a link failure, though the maximum delays could look a bit
high. Additionally, there are much more considerations behind fast
convergene than simply tuning the timers: e.g area sizing,
prefix-suppression, link redundancy and equal-cost multipathing, multicast
RPF throttling, additional OSPF timers tuning (LSA arrival delay, LSA
flooding delay). Lastly, it is important to notice that IS-IS has slightly
more "knobs" for fast performance tuning compared to OSPF (e.g. LSP
fast-flood or priority-driven prefix insertion - feature only supporeted by
OSPF in IOS-XR), but in general you may tune both protocols to achieve
practically the same convergence times.
In addition to the above document, I would recommend you reading the
following research paper:
http://inl.info.ucl.ac.be/publications/achieving-sub-second-igp-convergence-
As for IP Even Dampening timers, I made a short writeup on the timer
selection here http://blog.ine.com/2010/05/03/optimizing-ip-event-dampening/
. The use of IP Even Dampening overlaps with the LSA throttling feature for
ISIS/OSPF protocols, but it could be a very needful addition to EIGRP
networks. It does not hurt using IP Event dampening with any protocol, as
the default 30 second half-life value will suppress fast oscillation and
prevent additional work at OSPF/ISIS/EIGRP level, but stilll allows fast
convergence in response to the initial event.
HTH,
-- Petr Lapukhov, petr_at_INE.com CCIE #16379 (R&S/Security/SP/Voice) Internetwork Expert, Inc. http://www.INE.com Toll Free: 877-224-8987 Outside US: 775-826-4344 2010/5/22 Hussam EL Kebbi <hussamkibbi_at_hotmail.com>: > - How can I relate values needed from show ip ospf statistics to > values needed i throttle:? > output of show ip ospf statistic(where should I look at exactly) SPF > calculation timeDelta T Intra D-Intra Summ D-Summ Ext D-Ext Total > Reason00:10:10 0 0 0 0 0 0 0 R, 00:08:56 0 0 0 0 0 0 0 R, N, > > - if I used dampening only with no values, what the default it will take? > thanks > > > >> Date: Sat, 22 May 2010 09:52:02 +0000 >> From: joe_astorino_at_comcast.net >> To: hussamkibbi_at_hotmail.com >> CC: ccielab_at_groupstudy.com >> Subject: Re: OSPF Performance >> >> Well, you can use "show ip ospf statistics" to figure out how many >> times > things have flapped in some amount of time. The statistics you gather > from that effectively tell you the frequency of your flaps, which you > can then use to calculate things like the start, increment and max_wait. >> >> throttling SPF does ONLY that though -- it delays the running of SPF. > However, it has a similar IDEA as IP event dampening. The difference > is with throttling you are delaying the SPF from happening. With > dampening you are preventing instability by suppressing the > advertisements of LSAs when things are flapping. Both use the same > principal of how long to do that for (using exponential decay). >> >> So, to answer your second question it depends on what you want to do >> or what > you are told to do. Do you want to delay SPF calculations during > flaps, or do you want to prevent interfaces/networks from being > advertised at all during flaps, or both? >> >> HTH >> >> Regards, >> Joe Astorino, CCIE #24347 >> >> "He not busy being born is busy dying" -- Dylan >> >> ----- Original Message ----- >> From: "Hussam EL Kebbi" <hussamkibbi_at_hotmail.com> >> To: ccielab_at_groupstudy.com >> Sent: Saturday, May 22, 2010 5:26:14 AM GMT -05:00 US/Canada Eastern >> Subject: OSPF Performance >> >> Experts, >> According to ine bog: > http://blog.ine.com/2009/12/31/tuning-ospf-performance/ >> timers throttle spf start increment max_wait:is used when dynamic >> adaptation to unstable network topologies. >> 1 - How can we reflect the unstable network topologies timers (in >> throttle timers)?for example using: show ip ospf statistics? if so >> how can we relate output value to timers so we need to put in timers throttle? >> 2- It says also dampening would suppress events while throttling >> simply increases the response times: >> Do we need to use them together? >> Thanks >> >> >> >> _________________________________________________________________ >> Hotmail is redefining busy with tools for the New Busy. Get more from >> your inbox. >> > http://www.windowslive.com/campaign/thenewbusy?ocid=PID28326::T:WLMTAG > L:ON:WL >> :en-US:WM_HMP:042010_2 >> >> >> Blogs and organic groups at http://www.ccie.net >> >> _____________________________________________________________________ >> __ Subscription information may be found at: >> http://www.groupstudy.com/list/CCIELab.html >> >> >> Blogs and organic groups at http://www.ccie.net >> >> _____________________________________________________________________ >> __ Subscription information may be found at: >> http://www.groupstudy.com/list/CCIELab.html >> >> >> >> >> >> >> > > _________________________________________________________________ > Hotmail is redefining busy with tools for the New Busy. Get more from > your inbox. > http://www.windowslive.com/campaign/thenewbusy?ocid=PID28326::T:WLMTAG > L:ON:WL > :en-US:WM_HMP:042010_2 > > > Blogs and organic groups at http://www.ccie.net > > ______________________________________________________________________ > _ Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html Blogs and organic groups at http://www.ccie.netReceived on Sun May 23 2010 - 07:12:25 ART
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