Subject: Re: NSSA Test Case

From: Acee Lindem <[email-masked]>
Date: Thu, 6 Jan 2005 12:28:33 -0500

Mike Cleary wrote:

> Hello,
> I am trying to set up a test case where two routers advertise static 
> routes to the same network 3.3.3.0/24 with the same forwarding 
> address. I need one of the routers to be running in the backbone on 
> network 10.10.10.0/24 and both of the routers to be running in area 1 
> (nssa) on network 10.10.11.0/24.  I tried giving the routers a 
> forwarding address of 10.10.10.141 however one of them does not use 
> this as the forwarding address since it is not running on network 
> 10.10.10.0/24.

I guess if the P bit is clear there is no harm advertising a type 7 with 
an address
outside the NSSA. I don't believe this case is covered explicitly in RFC 
3101.

> I also tried advertising a forwarding address of 10.10.11.141 since 
> they will both be able to advertize this.  However the problem is that 
> I have a third router also running on network 1 and it installs the 
> route through 10.10.11.141 instead of chosing one of the two routers.

This is what it should do.

>   Does anyone know of a way to force the third router to chose one of 
> the two others to install the route through?  I have attached a 
> diagram that might be helpful.
> Thanks,
> ~Mike
>    
>
> ------------------------------------------------------------------------
>

---

From: Mike Cleary <[email-masked]>
Date: Thu, 6 Jan 2005 12:51:35 -0500

Hello Acee,
I was referring to this quote from RFC 3101 Section 2.4:

If an NSSA's border router originates a
   Type-5 LSA with a forwarding address from the NSSA, it should also
   originate a Type-7 LSA into the NSSA.  If two NSSA routers, both
   reachable from one another over the NSSA, originate functionally
   equivalent Type-7 LSAs (i.e., same destination, cost and non-zero
   forwarding address), then the router having the least preferred LSA
   should flush its LSA.  (See [OSPF] Section 12.4.4.1.)  Preference
   between two Type-7 LSAs is determined by the following tie breaker
   rules:

      1. An LSA with the P-bit set is preferred over one with the P-bit
         clear.

      2. If the P-bit settings are the same, the LSA with the higher
         router ID is preferred.

This leads me to believe that if two routers should be able to originate 
functionally equivalent Type-7 LSAs with a different P-bit setting and 
and third NSSA router should prefer one of them then there should be a 
way to check which is prefered.  The method I was using was checking in 
the routing table of the third router to see which of the other two 
routers it lists as the gateway.  Do you know of another way to observe 
which of the two routers the third chooses as a gateway for the route?
Thanks,
~Mike

Acee Lindem wrote:

> I guess if the P bit is clear there is no harm advertising a type 7 
> with an address
> outside the NSSA. I don't believe this case is covered explicitly in 
> RFC 3101.
>
>> they will both be able to advertize this.  However the problem is 
>> that I have a third router also running on network 1 and it installs 
>> the route through 10.10.11.141 instead of chosing one of the two 
>> routers.
>
>

-- 
*********************************************
Michael Cleary     Email: [email-masked]
IPv4 Consortium      UNH InterOperability Lab
121 Technology Dr., Suite 2, Durham, NH 03824
Phone: 603-862-3941    http://www.iol.unh.edu
*********************************************

---

From: Don Goodspeed <[email-masked]>
Date: Thu, 6 Jan 2005 11:16:35 -0800

Mike,

What if both the ABR/ASBR router and the NSSA ASBR router
both had another shared network in the nssa area 1 (say
10.10.12.0/24) that was OSPF enabled with the next-hop
residing on that network?

That should cause both ASBR to advertise the same fwding
address but the ABR will have the P-bit cleared.  Then
the DUT should choose a unique next-hop for the route
in question.

-don

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Mike Cleary
Sent: Thursday, January 06, 2005 9:52 AM
To: Mailing List
Cc: Acee Lindem
Subject: Re: NSSA Test Case

Hello Acee,