RE: IP ospf demand-circuit V/S IP ospf flood reduction ???

From: subodh.rawat@wipro.com
Date: Wed Aug 22 2007 - 08:21:40 ART

Shamim,

I read this in Cisco Press Book "Cisco IOS Cookbook, 2nd Edition".
Section "Recipe 8.18. Reducing OSPF Traffic in Stable Networks".

It reads like

"By default, OSPF will flood the area with all known LSAs every 3,600
seconds (1 hour). This is done as a sort of fail-safe to ensure that
whatever else might happen to the LSA database, it will be corrected at
least once an hour. In most networks this is unnecessary, as OSPF does a
good job of forwarding LSA messages whenever there is a change in the
network. But it is usually safe and may correct pathological conditions
where one or more LSAs have been dropped in the network, which is why
the designers of OSPF included the feature. However, if you are
concerned about the bandwidth overhead on your network, and if your
network is exceptionally stable, you can probably make do without this
fail-safe feature. "

I dont whom to trust; Cisco website or Cisco press book.

Regards
Subodh

________________________________

From: Shamin [mailto:ccie.xpert@gmail.com]
Sent: Wednesday, August 22, 2007 2:55 PM
To: Subodh Singh Rawat (WT01 - TELECOM SERVICE PROVIDER)
Cc: reto_ccie@yahoo.com; ccielab@groupstudy.com
Subject: Re: IP ospf demand-circuit V/S IP ospf flood reduction ???

Dear Subodh,

This is as per cisco website and as far as i know :

Each OSPF LSA has an age, which indicates whether the LSA is still
valid. Once the LSA reaches the maximum age (one hour), it is discarded.
During the aging process, the originating router sends a refresh packet
every 30 minutes to refresh the LSA. Refresh packets are sent to keep
the LSA from expiring, whether there has been a change in the network
topology or not. Checksumming is performed on all LSAs every 10 minutes.
The router keeps track of LSAs it generates and LSAs it receives from
other routers. The router refreshes LSAs it generated; it ages the LSAs
it received from other routers.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1826/products_feature_
guide09186a0080087d4d.html

But I will appreciate if you can clarify me as to the differences
between "ip ospf flood reduction " & " ip ospd demand -circuit"

Regards
Shamin

On 8/22/07, subodh.rawat@wipro.com < subodh.rawat@wipro.com
<mailto:subodh.rawat@wipro.com> > wrote:

        Just to correct you: This refreshment of LSA takes place after 1
hour
        not 30 minutes.

        Subodh

        -----Original Message-----
        From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf Of
        eicc tester
        Sent: Wednesday, August 22, 2007 4:38 AM
        To: Shamin; Cisco certification
        Subject: Re: IP ospf demand-circuit V/S IP ospf flood reduction
???

        Hi

          "ip ospf flood reduction" just avoid the refreshement of LSA
every 30
        minutes.

          "ip ospf demand circuit" mean that a link which is under an
OSPF area
        , don,t send OSPF hello packet all the time. This avoid the fact
of
        bring the circuit (probaly and dial or isdn) just for sent hello
packet
        periodically, the neigbhor relations is still maintaned.

        Shamin <ccie.xpert@gmail.com> wrote:
          Hi All,

        Can any one tell me , when the commands "ip ospf flood
reduction" is
        used over " ip ospf demand circuit" .
        I know that, "Ip ospf demand circuit is used in point to point
        connections.
        Does that mean, ip ospf flood reduction"
        is used in Broadcast and NBMA OSPF networks. I am bit confused
as to
        which command to apply in a particular scenario, mainly if the
question
        asks to reduce the "paranoid updates" in ospf that occurs every
30mins.

        Thanks in advance.

        Regards
        Shamin

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