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OSPF and nssa area

[ Edited ]
‎10-31-2019 07:16 AM

Hi There,

I need to connect legacy networks with new device therefore i do not want to modify too much the legacy configuration.

Topology: very easy

- 2 ASBR, named R1-ASBR and R2-ASBR

- 2 Internal Router, named R1-Internal R2-Internal

- Ospf area: area 0.0.0.0 and area 0.0.1.6 (plus many others area)

- Of course: R1-ASBR and R2-ASBR  are connected to area 0.0.0.0 and area 0.0.1.6 plus they have eBGP connections with other routers

- R1-ASBR and R2-ASBR, R1-Internal R2-Internal, belong to area 0.0.1.6 and they have connected networks (vrrp)

- area 0.0.1.6 is an nssa area (I can not modify it. It must be an nssa)

- There are more area connected to the 2 ASBR but they all have the same topology: 2 internal routers connected to these 2 ASBR.

Target:

I want to configure the area area 0.0.1.6 as the following:

- Prevents the ASBR/ABR from advertising summary routes into the NSSA.: no LSA-3 (Inter-area summary routes), no LSA-7 (external routes)

- ASBR/ABR inject a default-route

- The area allow only routes internal to the area

 

Reference: https://www.juniper.net/documentation/en_US/junos/topics/example/ospf-not-so-stubby-area-configuring...

However i found the above reference a bit confused.

I like to run the following config in the ASBR (I am just focus on nssa area so no interface  or general ospf cponfig are listed)

 

set protocols ospf area 0.0.1.106 nssa default-lsa type-7
set protocols ospf area 0.0.1.106 nssa default-lsa default-metric 10
set protocols ospf area 0.0.1.106 nssa no-summaries

 

Why this?

no-summaries—"Prevents the ABR from advertising summary routes into the NSSA" -> I am assuming LSA-3??? or LSA-7??

default-metric statement - "If configured in combination with the default-metric statement, the NSSA only allows routes internal to the area and advertises the default route into the area. External routes and destinations to other areas are no longer summarized or allowed into the NSSA."  -> I am assuming no LSA-7 and LSA-3 basically. Do you agree?

So far so good.

 

Problem is with the following command

default-lsa type-7

Explanation from the above link:

type-7—(Optional) Floods Type 7 default LSAs into the NSSA if the no-summaries statement is configured. By default, when the no-summaries statement is configured, a Type 3 LSA is injected into NSSAs for Junos OS release 5.0 and later. To support backward compatibility with earlier Junos OS releases, include the type-7 statement.

 

My concerns:

  • "By default, when the no-summaries statement is configured, a Type 3 LSA is injected into NSSAs for Junos OS release 5.0 and later."  ->  statement no-summaries block LSA-7 but not LSA-3 ????
  • If i add default-lsa type-7 I am going to block also LSA-7 ???

Is this correct?

If yes than basically  i have a Totally Stubby Area + default-route.

So is really unclear the effect of the below

 

set protocols ospf area 0.0.1.106 nssa default-lsa type-7
set protocols ospf area 0.0.1.106 nssa default-lsa default-metric 10
set protocols ospf area 0.0.1.106 nssa no-summaries

 

Again I need to work with nssa just for configuration reason.

 

Thanks.

 

 

 

3 REPLIES 3
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Routing

Re: OSPF and nssa area

[ Edited ]
‎10-31-2019 07:34 PM

When you configure an ABR connected to an NSSA, there are 3 options: 

 

1) If you configure the ABR with:

 

           set area 0.0.0.0 nssa default-lsa default-metric 10

 

the ABR will inject:

  • a default route as a type-7 LSA AND
  • LSAs type 3 (for prefixes in other areas) 

2) If you configure the ABR with:

 

set area 0.0.0.0 nssa default-lsa default-metric 10 AND

set area 0.0.0.0 nssa no-summaries

 

the ABR will inject:

  • a default route as a type-3 LSA   
  • NO other LSAs type 3 (for prefixes in other areas) 

3) If you configure the ABR with:

 

set area 0.0.0.0 nssa default-lsa default-metric 10 AND

set area 0.0.0.0 nssa default-lsa type-7 AND

set area 0.0.0.0 nssa no-summaries

 

the ABR will inject:

  • a default route as a type-7 LSA   
  • NO LSAs type 3 (for prefixes in other areas) 

 

 

OSPF.png

 

HTH,

Yasmin Lara - Juniper Ambassador #QuadE - JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
JNCIS-CLOUD, JNCDS-DC, JNCIA-DevOps
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Re: OSPF and nssa area

‎11-05-2019 07:49 AM

Thank you so much for this summary.

I like your solution

 

set area 0.0.0.0 nssa default-lsa default-metric 10 AND

set area 0.0.0.0 nssa default-lsa type-7 AND

set area 0.0.0.0 nssa no-summaries

 

the ABR will inject:

  • a default route as a type-7 LSA   
  • NO LSAs type 3 (for prefixes in other areas) 

 

But what about the external prefixes that ASBR is earning from BGP? I do not want that ASBR will inject them inot the nssa. Thanks.

Routing

Re: OSPF and nssa area

‎11-06-2019 06:26 PM

I thought I had replied, but seems like I didn't.  From what I am understanding you want to do, I think configuring no-asbr-abr under protocols OSPF on your ASBR/ABR router should work.  

 

HTH,

Yasmin Lara - Juniper Ambassador #QuadE - JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
JNCIS-CLOUD, JNCDS-DC, JNCIA-DevOps
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