ospf network

Unanswered Question
Feb 11th, 2007

hi,

im having 3 routers connected together in a triangle in three seperate areas Area1,Area2,Area3 and Area0 for interconnection in between.

ospf is configured on all of these point-to-point network .

Right now im having these three areaa ie:Area1,Area2,Area3 configured as nssa areas.

i need to know why it has been configured in such a manner when i dont have any more networks beyond this .

could ther be a more efficient way to utilise / configure.??

Thanks in advance

I have this problem too.
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royalblues Sun, 02/11/2007 - 07:40

Hi gaurav,

The idea of having areas is to reduce the routing information & the LSA database that needs to be carried by each router.

By configuring certain area types the amount of LSA propogation is reduces still allowing reachability to all destinations.

If a particular area has just a single exit out of that area through an ABR then the area is generally configured as stub.

Stub areas do not carry any type 5 LSA. Because of this this area cannot be redistribute external information. To overcome this limitation the areas are configured as NSSA (not so stubby area) which inherits most of the stub features but also allows an ASBR to exist in the network.

This could only be the reason why they are configured as NSSA.

Have a look at this link

http://www.cisco.com/warp/public/104/8.html

HTH, rate if it does

Narayan

gauravm Sun, 02/11/2007 - 09:24

thanks narayan,

i understand why the areas have been created ,to reduce LSA etc but my query is cant we have the network without these areas configured as nssa since we are not running any other routing protocol .

if yes, what implications it could ??

i hope im able to make it clear ??

thanks in advance

sundar.palaniappan Sun, 02/11/2007 - 09:41

Your situation doesn't warrant the need for NSSA. As explained by the previous poster, NSSA is configured to prevent type 5, aka. external, LSAs from coming into this area. Since, your exisiting setup doesn't have the presence of any external LSAs the configuration you have in there now isn't ideal setup. All 3 routers in your setup are ABRs and would learn only type 1 - 3 LSAs only. If you desire you can configure them all as standard OSPF areas.

HTH

Sundar

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