adding OSPF NSSA totally stub area

[shartley]

Basically, will adding a new area (in this case, NSSA totally stub) cause a reconvergance in Area 0? I don't believe so but was asked to check by adding a new discussion. More details:

1) The links to the new area will be defined as Pt-to-Pt

2) The stub area is to originate a smaller subnet of a network I am already advertising via Area 0

3) I was going to add these statements to the ABR(s):

     area 1 nssa default-information originate

     area 1 nssa no-summary

[Peter Paluch]

Hello,

will adding a new area (in this case, NSSA totally stub) cause a reconvergance in Area 0?

This depends on what you understand under reconvergence. Adding the new area should not cause any transient connectivity outages in the backbone area. It will nevertheless cause something IS-IS would call "Partial Route Calculation" - a less intensive reconvergence which is based on the fact that the prefixes from  the new NSSA-TS area will be imported into the backbone as LSA-3/LSA-4/LSA-5 and routers will need to update their routing tables.

2) The stub area is to originate a smaller subnet of a network I am already advertising via Area 0

I do not entirely understand this one. Can you provide an example please?

3) I was going to add these statements to the ABR(s):
     area 1 nssa default-information originate
     area 1 nssa no-summary

If "area 1 nssa no-summary" is used then the "default-information-originate" shall not be used. The default route will be injected into the NSSA-TS area automatically. The "area 1 nssa default-information-originate" is used only if the area is a pure NSSA, not NSSA-TS.

Best regards,

Peter

[shartley]

Thanks for replying so quickly! Regarding your request for an example of the network to be advertised via the NSSA: In area 0 we are currently advertising a /20 and in area 1 (NSSA) we are planning to advertise a /24 from that larger subnet. Does this break the rule of advertising the same subnet from two areas?