From: Narbik Kocharians (narbikk@gmail.com)
Date: Wed Aug 22 2007 - 12:17:34 ART
The "OSPF Flooding Reduction" and the "demand circuit" works by reducing
unnecessary refreshing and flooding of already known and unchanged
information with a difference:
In OSPF demand circuit, hellos and the flooding of the LSAs are suppressed,
whereas, in flood reduction, the flooding of the LSAs are suppressed only
and NOT the hellos.
If you forget CCIE lab exam for a minute you will see that in real world
implementation, when it comes to dialup networks, you would want to suppress
the unnecessary refreshing AND the hellos, because you don't want either one
of them to bring up the link. But in dedicated connections you don't really
care about the hellos as much but you do not want the refreshing to occur
every 30 minutes. Therefore, for dialup connection you use demand circuit
and dedicated connections you would use flood reduction.
But in CCIE everything goes, because they are testing you based on your
experience and understanding, since we don't have a dialup connection in the
CCIE exam, how would they test to see if you know what you are talking
about? This is why you may see these used on dedicated circuits as well.
On 8/22/07, Scott Morris <smorris@ipexpert.com> wrote:
>
> Flood reduction on a demand circuit would be redundant. That's one of the
> features of demand circuit. (RFC 1793 if you're bored)
>
> Demand circuit is also used for hello suppression between two neighbors,
> to
> make things quieter.
>
> So both methods reduce the overall traffic flow on a link, just approach
> it
> differently based on the link-type. Knowing the details of both should
> help
> you make the correct decision if faced with it in the lab!
>
> HTH,
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
> #153, CISSP, et al.
> CCSI/JNCI-M/JNCI-J
> VP - Technical Training - IPexpert, Inc.
> IPexpert Sr. Technical Instructor
>
> A Cisco Learning Partner - We Accept Learning Credits!
>
> smorris@ipexpert.com
>
> Telephone: +1.810.326.1444
> Fax: +1.810.454.0130
> http://www.ipexpert.com
>
>
> _____
>
> From: Shamin [mailto:ccie.xpert@gmail.com]
> Sent: Wednesday, August 22, 2007 10:14 AM
> To: smorris@ipexpert.com
> Cc: subodh.rawat@wipro.com; reto_ccie@yahoo.com; ccielab@groupstudy.com
> Subject: Re: IP ospf demand-circuit V/S IP ospf flood reduction ???
>
>
> Scott,
>
> Thank you for your clarification.
>
> If you can clarify my original concern ,i will be grateful i.e when to use
> " ip ospf demand-circuit " v/s " ip ospf flood reduction".
> I know that, demand-circuit is used over p-t-p networks. But is the
> functionality of the two commands the same when it comes
> to reducing the LSA refresh. Furthermore, can " ip ospf flood reduction
> command " be used on a demand circuit,
>
> Thanks in advance
>
> Regards
> Shamin
>
>
> On 8/22/07, Scott Morris <smorris@ipexpert.com> wrote:
>
> Per Appendix B of RFC 2328:
>
> "LSRefreshTime
> The maximum time between distinct originations of any particular
> LSA. If the LS age field of one of the router's self-originated
> LSAs reaches the value LSRefreshTime, a new instance of the LSA
> is originated, even though the contents of the LSA (apart from
> the LSA header) will be the same. The value of LSRefreshTime is
> set to 30 minutes."
>
> "MaxAge
> The maximum age that an LSA can attain. When an LSA's LS age
> field reaches MaxAge, it is reflooded in an attempt to flush the
> LSA from the routing domain (See Section 14). LSAs of age MaxAge
> are not used in the routing table calculation. The value of
> MaxAge is set to 1 hour."
>
> The re-flooding occurs at half of maxage (30 minutes).
>
> HTH,
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
> #153, CISSP, et al.
> CCSI/JNCI-M/JNCI-J
> VP - Technical Training - IPexpert, Inc.
> IPexpert Sr. Technical Instructor
>
> A Cisco Learning Partner - We Accept Learning Credits!
>
> smorris@ipexpert.com <mailto:smorris@ipexpert.com>
>
> Telephone: +1.810.326.1444
> Fax: +1.810.454.0130
> http://www.ipexpert.com
>
>
> -----Original Message-----
> From: nobody@groupstudy.com <mailto:nobody@groupstudy.com>
> [mailto:nobody@groupstudy.com] On Behalf Of
> subodh.rawat@wipro.com
> Sent: Wednesday, August 22, 2007 4:39 AM
> To: reto_ccie@yahoo.com; ccie.xpert@gmail.com; ccielab@groupstudy.com
> Subject: RE: IP ospf demand-circuit V/S IP ospf flood reduction ???
>
> 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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-- Narbik Kocharians CCIE# 12410 (R&S, SP, Security) CCSI# 30832 www.Net-WorkBooks.com
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