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In which scenario we are using Stub area,totally stub area,not so stubby area..

Please let me know in which network scenario we are using Stub area,totally stub area,not so stubby area..          It will be great if you come with easy examples....

Regards,

Sumit

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Beginner

In which scenario we are using Stub area,totally stub area,not s

http://simplecisco.wordpress.com/2012/12/21/ospf-stub-totally-stubby-areas/

In the diagram above you have (area 1) connecting to the backbone (area 0) via ABR R2.

Assume R1 in (area 0) is an ASBR injecting external routes via redistribution into the area. These routes will be injected as Type 5.

To reduce LSA advertisments in (area 1), router R2 may not inject these type 5 LSAs into (area 1).

Instead (area 1) routers will rely on a default route to (area 0) to reach external destinations.

Therefore, ABR R2 does not need to send Type 4 LSA to (area 1). When a Type 5 is not advertised an Type 4 is not needed. This configuration makes (area 1) as Stub Area.

Further, you can block Type 3 LSAs on (area 1) and rely on a single Type 3 LSA representing a default route.

This default will send traffic originating in (area 1) and destined to a different area or an external destination towards the backbone (area 0).

This configuration makes your (area 1) a Totally-Stubby Area reducing your LSA advdertisments and hence your OSPF database size in the area.

Now imagine your design goal changes, and you want to advertise external routes via an ASBR that belongs to (area 1).

Since ASBR's typically advertise a Type 5 and your (area 1) is configured to block type 5 LSAs, you can configure (area 1) as a Not-so-Stubby Area.


This allows the ASBR to advertise external destinations as Type 7 instead of Type 5 into (Area 1) and to the rest of the OSPF domain if you wish.

Hope this helps.

kind regards, Eehab

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Highlighted
Beginner

In which scenario we are using Stub area,totally stub area,not s

http://simplecisco.wordpress.com/2012/12/21/ospf-stub-totally-stubby-areas/

In the diagram above you have (area 1) connecting to the backbone (area 0) via ABR R2.

Assume R1 in (area 0) is an ASBR injecting external routes via redistribution into the area. These routes will be injected as Type 5.

To reduce LSA advertisments in (area 1), router R2 may not inject these type 5 LSAs into (area 1).

Instead (area 1) routers will rely on a default route to (area 0) to reach external destinations.

Therefore, ABR R2 does not need to send Type 4 LSA to (area 1). When a Type 5 is not advertised an Type 4 is not needed. This configuration makes (area 1) as Stub Area.

Further, you can block Type 3 LSAs on (area 1) and rely on a single Type 3 LSA representing a default route.

This default will send traffic originating in (area 1) and destined to a different area or an external destination towards the backbone (area 0).

This configuration makes your (area 1) a Totally-Stubby Area reducing your LSA advdertisments and hence your OSPF database size in the area.

Now imagine your design goal changes, and you want to advertise external routes via an ASBR that belongs to (area 1).

Since ASBR's typically advertise a Type 5 and your (area 1) is configured to block type 5 LSAs, you can configure (area 1) as a Not-so-Stubby Area.


This allows the ASBR to advertise external destinations as Type 7 instead of Type 5 into (Area 1) and to the rest of the OSPF domain if you wish.

Hope this helps.

kind regards, Eehab

Beginner

Re:In which scenario we are using Stub area,totally stub area,no

Stub area : In any ospf area when we dont want to receive any type4 & type5 lsa then that area is configd as stud area .
Totally stub area : In any ospf area if we dont want to receive type3 , 4 & 5 lsa then that area is configd as a totally stub area .
NSSA : When asbr is used in stud/total stub area then not to void stud areas concept NSSA is used . In NSSA all type5 lsa are created as type7 lsa which further gets conveted to type5 lsa at asbrs .


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Engager

Re: In which scenario we are using Stub area,totally stub area,n

Hi Sumit,

the other postings already describe most of the technical issues, I'd like to add some design considerations because you've ask for scenarios.

The original purpose of stub areas was to save router resources, especially memory. Although hardware capabilities have improved considerably since the 90s, this still applies to today's networks.

Imaginge the redistribution of a large amount of BGP routes into your OSPF Backbone Area.

If you had to interconnect a small site with only a few low-end routers, you possibly couldn't enable OSPF here until you replace the routers with more powerful ones.

If you have an area (e.g. the small site mentioned in the example above) which has only one single exit point, that's like leaving a dead-end street: You don't need to have detailed information about all the possible destinations at this point, knowning the direction to leave it is sufficient. This scenario correspondes to a totally stub area: A default route will be injected replacing the detailed information about the outside world and that's it. Minimal consumption of router memory, CPU and bandwidth.

If you have more than one exit point, the use of a totally stub area could lead to suboptimal or undesired forwarding paths. By using a "normal" stub area instead you can achieve a better path selection at least for inter area destinations, external destinations will still be replaced by default routes. Of course this consumes some more resources but you're still rid of all the external prefixes.

A NSSA adds the possibilty of distributing the prefixes of a small external routing domain (e.g. a RIP cloud or some static routes) into the rest of the OSPF domain.

Also form a design perspective the injection of a default route by stub areas can be something very welcome, e.g. when you're using static default-routes in the backbone area but can't inject them into OSPF for some reason.

If you need to use an area for a virtual link, you can't configure it as a stub area.

Hope that helps

Rolf

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