From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Sun May 16 2004 - 23:26:10 GMT-3
>Hi Howard,
>
>Howard,
>
>First let me thank you for the prompt reply.
>
>I understand that these commands are more effective when used in large
>environments. As you have mentioned in your reply,
>with the ospf demand circuit we can suppress ospf hellos and reflooding of
>aged out SLAs. My understanding is that routers with a demand circuit will
>not age out all LSA that the router received over the demand circuit and
>will not resend locally generated and other LSAs over that circuit. If this
>router has a another normal(non demand cuircuit) connection, then all LSAs
>will be flooded over that connection. Pls correct me if I am wrong. I am
>just trying to understand what router does in this situation.
>Please could you tell me what router is actually doing when there is
>interface with ip ospf database-filter, cisco doc says it
>stops LSA flooding on that interface. Does that mean the router treat the
>interface as a demand circuit by only blocking LSA floods and sending OSPF
>hellos? and what happen if it stops sending LSA to the neighbour. will the
>Neighbour loose all lsa info from that client?
It is my understanding this is effectively doing what demand circuit
does, and just documents a functionality. IIRC, it sets the Do Not
Age bit on all LSAs, so it doesn't ever age them out, the receiver
doesn't age them out, etc.
>What it does with locally
>generated LSAs? are they also suppressed on this interface?
>I can understand that Ip ospf flood-reduction simply increase LSA age out
>time and therefore reduce floods to others.
It doesn't increase the aging time. It disables aging completely.
The wording could be much more clear. I'm trying to remember a
conversation with a developer a while back, and may have to send out
some emails during the week to people with code access.
>
>I appreciate your advice on this.
>
>Thanks
>
>Emil
>
>
>
>
>
>
>
>-----Original Message-----
>From: Howard C. Berkowitz [mailto:hcb@gettcomm.com]
>Sent: Monday, 17 May 2004 10:49 AM
>To: ccielab@groupstudy.com
>Subject: Re: OSPF LSA filtering
>
>
>At 7:59 AM +1000 5/17/04, Fernando, Emil wrote:
>>Hi Group,)
>>
>>In OSPF there are two interface commands ( ip ospf database-filter and
>ip
>>ospf flood-reduction ) that we can use to improve bandwidth usage.
>>Can someone help me to understand when I should use these commands and
>which
>>command is more effective than the other one. What OSPF does when these
>>commands ara enabled ? Can I use these commands on a tail site to improve
>>the routing performance of the tail site ?
>>
>
>Before trying to use these features, first, how have you determined
>there is a bandwidth problem that needs to be fixed, or how would you
>approach it? Second, if there is a bandwidth problem, there may be
>better ways to fix it than tuning OSPF at the protocol level.
>
>Still within OSPF, one reason you may have a bandwidth problem is
>that your areas are too large, or have too many inter-area/external
>routes injected into them. Due to such sizing, there may be too many
>LSAs to transfer, and they may not, in any case, be useful to tail
>routers.
>
>Flooding reduction is intented for large, stable networks, as often
>found in ISPs or some well-run enterprise networks. You can think of
>it as a means of applying the logic in the demand circuit extension
>to general OSPF, which stops reflooding LSAs simply because they have
>aged out, and only refloods when a significant topological event
>occurs. The desire to minimize updates in large, stable networks is
>one reason many ISPs use ISIS as their IGPs, because ISIS has always
>had good facilities for minimizing updates in what can be single
>areas of over 1000 routers. See
>http://www.cisco.com/en/US/products/sw/iosswrel/ps1834/products_feature_guid
>e09186a008008011e.html
>--
>============================================================================
>===
>"What Problem are you trying to solve?"
>***send Cisco questions to the list, so all can benefit -- not
>directly to me***
>****************************************************************************
>****
>Howard C. Berkowitz
> presentation downloads by anonymous ftp from www.netcases.net.
>
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