From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Sun Jul 06 2008 - 01:29:34 ART
The best practice would probably not to rely on ISIS timers to increase
convergence speed ;) Optimally, you would like to use physical layer
mechanics to detect a link failure quickly and reliably (e.g. use POS
interfaces). However, if you are unlucky enough to run ethernet links (sigh)
as we usually do in enterprise networks, you may consider the followin
options:
1) Use point-to-point links (e.g. L3 interfaces, not switchports/SVIs) for
ethernet and set "carrier-delay 0" to maximize link failure response. Also
seting ISIS nework-type "point-to-point" would somewhat minimize LSP
database size, though this is not a big issue.
2) Use interface-level IP event dampening to prevent a flapping link from
affecting the entire topology
3) Use ISIS fast-hellos for sub-second detection of link failure OR
4) Use BFD for even better link failure detection. BFD is data-plane
feature, and thus allows for optimized implementation in line cards thereby
allowing to reduce load on RSP. Additonally, BFD may provide faster
detection times than fast-hellos and is L3 protocol agnostic.
All those recommendations optimize link failure detection time.
Additionally, you may want to tune global ISIS timers, such as SPF/PRC
calculations and LSP generation timers to enforce ISIS perform updates in
more expedite manner (resulting in additional CPU penalties). For instance,
you may set "spf-inteval" and "prc-interval" to minimal values e.g.
"spf-interval 1 1 10".
Last but not least - make your network design is scalable and allow
effective summarization, for this reduces LSP database sizes and increases
stability. You may end up with summarization not possible due to MPLS
deployment scenario, but there are workarounds (such as inter-area TE or use
of BGP for label distribution). Also they work on a standard (currently
there are exist a couple of drafts) which allows for summarization to work
with MPLS/LDP/IGP deployments.
-- Petr Lapukhov, CCIE #16379 (R&S/Security/SP/Voice) petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com
2008/7/5 Jim Scheller (jschelle) <jschelle@cisco.com>:
> Is there a "best practice" on ISIS timers for quick > recovery/convergence? > -Jim > > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Mon Aug 04 2008 - 06:11:53 ART