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New Member

OSPF area 0 on ISDN Link ?

Hi All,

Can I define my OSPF area 0 on ISDN link ?

What's the effect to others area ?

Would you please some one try it on the lab ?

I am looking forward to hear from you.





Re: OSPF area 0 on ISDN Link ?


You can define area 0 on a ISDN link. There isn't a limitation or anything preventing this.

A possible issue is if you have several other routers in area 0 without ISDN lets say that are stable (no link flaps, etc). The OSPF SPF process after it is initially ran is relatively quiet. ISDN links may go down and come up often, etc. Each time ISDN link flaps this will cause OSPF to run SPF again for area 0. You'll lose routes during the reconvergence and router CPU will spike up during this time a little bit. This all depends on how many routes and OSPF interfaces are in area 0.

Placing the ISDN links in their own area will help keep the backbone area more stable. Theres also a feature called demand-circuit which keeps OSPF traffic at a minimim on ISDN/dial circuits.

Hope this helps. This all really depends on you're network design (area placement, etc).


New Member

Re: OSPF area 0 on ISDN Link ?

Hi Erick,

Thanks for your response.

So in other words, area 0 on a ISDN link is not recommended for good/better OSPF design, is it?

I've plan to separate the ISDN router for that branch from the router for other branches that using F/R, then Ethernet connection between the ISDN router and the other router become the Area 0, what's your opinion about it ?



Re: OSPF area 0 on ISDN Link ?