NSSA Default-Information-Originate

jskfan
jskfan used Ask the Experts™
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NSSA Default-Information-Originate

I would like to know  the OSPF area type where we use  the command NSS Default-Information-Originate

---On Stub area : we configure all routers inside the are with : Area X  Stub
--- On Totally Stub : we configure all routers inside the area with :Area X Stub, and the ABR with Area X Stub Non-Summary
---On NSSA area  : We configure all routers inside the are with : Area X NSSA
--- On Totally NSSA: We configure all router inside the are with : Area X NSSA and the ABR with Area X NSSA Non-Summary

However I am not sure how we call the area type where we configure :NSS Default-Information-Originate


Thank you
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Distinguished Expert 2018

Commented:
stub area, totally stubby area and totally  NSSA - default route is added automatically by ABR (default option)

 NSSA ASBRs - default-Information originate is added, but ASBR needs to have default route in routing table to be able to advertise default route
 NSSA - ABR need command to advertise default route into NSSA (area X nssa default-information-originate)

I am not sure that all cases are covered here.

Author

Commented:
how do you call the Stuby Area where  this commane is used   :
area X nssa default-information-originate

is it NSSA ot Totally NSSA  or it has another name ?
Distinguished Expert 2018

Commented:
It is NSSA.
area X nssa
Totally NSSA is configure with:
area X nssa no-summary
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Author

Commented:
Because there is another area where you configure all its  routers with only : Area X NSSA

I mean you do not configure the ABR with Area X NSSA Deafult-Information-Orginate

Author

Commented:
So there is :
1 - Area X NSSA  
Not So Stubby Area

2 - Area X NSSA No-Summary
Totally Not So Stubby Area

3 - Area X NSSA Default-Information-Originates

Not Sure ???
Distinguished Expert 2018
Commented:
3 - not so stubby area + ABR advertises default route into nssa (1 may not advertise default route into nssa by itself, that's why default-information-originate is part of the command - to specify "advertise summary route (summary default route) into nssa")
Ibrahim KasabriInfrastructure admin

Commented:
DEAR,

To understand why we use this command when we configure NSSA in ABR on OSPF configuration " area X nssa default-information originate"
you have to know the types of link state advertisement (LSA) that generated by OSPF routers and exchanged between them to update, the optimum path to the destination.

A quick example

1234.gif
R1 is NSSA ABR  
R3 is  NSSA ASBR connected to IGRP

Now the IGRP routes will be redistributed to OSPF area 1, then readvertise them with default route  Via R3 to all routers in area 1 as LSA type 7 which is called  NSSA external and it appears on R3 route table as EX
when the LSA type 7  reached the ABR, R1 will not allow it to pass through by using this command on OSPF process " NSSA default information originated"  translates LSA Type 7 into an LSA Type 5 and floods it into the OSPF network and can be seen in the routeing table as OE1 or OE2.


for more information about OSPF LSA see the link below
http://www.firewall.cx/networking-topics/routing/ospf-routing-protocol/1178-ospf-lsa-types-explained.html
 or
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/6208-nssa.html

Author

Commented:
Thank you Guys

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