From: ALL From_NJ (all.from.nj@gmail.com)
Date: Wed Feb 18 2009 - 14:32:12 ARST
Here is the link to the ospf demand circuit docs (watch the ugly word wrap)
http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_ospf_cfg_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1054646
W/ demand circuits your link may still come up to exchange needed routing
updates ... no worries there this is required for OSPF to maintain a
consistent database.
Here is a copy as paste from the link above:
With this feature, periodic hellos are suppressed and the periodic refreshes
of LSAs are not flooded over the demand circuit. These packets bring up the
link only when they are exchanged for the first time, or when a change
occurs in the information they contain. This operation allows the underlying
data link layer to be closed when the network topology is stable.
This feature is useful when you want to connect telecommuters or branch
offices to an OSPF backbone at a central site. In this case, OSPF for
on-demand circuits allows the benefits of OSPF over the entire domain,
without excess connection costs. Periodic refreshes of hello updates, LSA
updates, and other protocol overhead are prevented from enabling the
on-demand circuit when there is no "real" data to send.
Overhead protocols such as hellos and LSAs are transferred over the
on-demand circuit only upon initial setup and when they reflect a change in
the topology. This means that critical changes to the topology that require
new SPF calculations are sent in order to maintain network topology
integrity. Periodic refreshes that do not include changes, however, are not
sent across the link.
I am not sure I fully understand your last statement about only needing the
link to come up when the primary goes down.
Configuring the ISDN as a backup or fail over link is not necessarily
related to OSPF. What I mean is, you can have this backup functionality
without OSPF running over the link. OSPF demand circuit is needed when you
want to exchange OSPF routing info, and you do not want OSPF to keep the
ISDN link up.
Configure it as a demand cirtuit, and all is quiet ... unless ofcourse there
are changes to the topolog.
HTH,
Andrew Lee Lissitz
On Wed, Feb 18, 2009 at 5:23 AM, Fahad Khan <fahad.khan@gmail.com> wrote:
> Dear experts,
>
> Hope you all are doing fine.
>
> In ospf demand circuit (ISDN dial backup), I have seen that although
> routing
> updates are reduced but the periodic LSAs are still being sent in evern
> 20-30 minutes. And my isdn interface is bound to dial after every 20-30
> minutes even my primary link is up.
>
> My requirement is to make my isdn (backup) link to dial only when my
> primary
> link (DXX) fails.
>
> The link type is point-to-point.
>
> Is this RFC based?? I mean the the routing updates are reduced due to
> demand circuit or fully eliminated???
>
> waiting for the responce
>
> thanks and regards,
>
> --
> Muhammad Fahad Khan
> IT Specialist
> Global Technology Services, IBM
> +92-321-2370510
> +92-301-8247638
> http://fahad-internetworker.blogspot.com
>
>
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-- Andrew Lee Lissitz all.from.nj@gmail.comBlogs and organic groups at http://www.ccie.net
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