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New Member

ip ospf demand-circuit of dialer watch-list?

Hi all,

when config ospf link redundancy using isdn for backup is the command "ip ospf demand-circuit" can make it or use "dialer watch-list" ? Thank you!

Best Regards

Teru Lei

4 REPLIES

Re: ip ospf demand-circuit of dialer watch-list?

Demand Circuit should do. No need for watch-list.

Demand circuit, forces a hello exchange initially to form neighbor relationship between adjacent routers. Once a hello is exchanged, each router will have the other neighbor with a dead time = "-" (see this in show ip ospf neighbor)

The dead time is not incremented for this neighbor, to prevent removal of the neighbor from the neighbor table, after every 40 sec.

Once the primary link goes down, ospf dials the ISDN link automatically and the network would converge over the ISDN link.

Hope that helps

New Member

Re: ip ospf demand-circuit of dialer watch-list?

You can use either (but not both together). OSPF Demand Circuit is the "official" way to do this, but has its drawbacks as it requires careful OSPF area design for optimal use of the dialer link. Dialer Watch, however, works very simply but has the drawback that the dialer goes up and stays up as long as there is no other route to the watched networks.

Hope this helps.

Cisco Employee

Re: ip ospf demand-circuit of dialer watch-list?

I would prefer a dialer watch-list as the backup line can be activated once the watched route is flushed from the routing table.

New Member

Re: ip ospf demand-circuit of dialer watch-list?

Hi,

Thank You for your answer. I also think I should do so. But if the primary is frame-relay (and that's a very common in CCbootCamp), And I found the answer of CCbootCamp is to use "ip ospf demand-circuit", And somebody said that the reason is if you use watch-list and the frame-relay circuit number is mis-config in the frame-relay switch, the isdn link will not go up (because in that case the connected interface is still up). So do you have any further comment? Thank You!

Best Regards

Teru Lei

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