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Re: Choosing among multiple intra-area ASBR routers posted 02/07/2002
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Hi, Sherry.

I know what you are talking about.
I've had the same confusion for this, but it's still very foggy.
A while ago, I myself posted this question but there were no satisfactory replies.

http://www.groupstudy.com/archives/ccielab/200105/msg01134.html

There was a posting for this in "OSPF" mailing list. It sure is a very confusing subject!
You can find the clear explanation from John Moy.

Question: http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0107&L=OSPF&P=R5138
John's answer: http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0107&L=OSPF&P=R6333&m=2564

Well, I have concluded from my own short lab sessions that in a default configuration, Cisco's implementation doesn't conform to RFC2328 when it comes to the path selection over multiple intra-area paths to ASBR.
That means there's no preference for non-backbone intra-area path to ASBR over backbone intra-area paths to ASBR.

But there's a mysterious command which seems to be a knob to make a Cisco box conform to RFC2328, I suspect.
That's "no compatible rfc1583" command under the router configuration. ("compatible rfc1583" is default)

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r/iprprt2/1rdospf.htm#xtocid79699

I think it's worth doing some lab with this command, "no compatible rfc1583".
Sorry I can't do it myself because of the lack of equipments, :(
If you find anything about this command's  behavior, please let me know it.

Jaeheon,

----- Original Message ----- 
From: "sherry huies" <cholscurry@xxxxxxxxxxx>
To: <ccielab@xxxxxxxxxxxxxx>
Sent: Thursday, February 07, 2002 10:43 PM
Subject: Choosing among multiple intra-area ASBR routers 


> 
> Hi, all
> According to rfc2328. p.175, when we have multiple
> intra-area paths to ASBR,
> a intra-area path using non-backbone area should be
> chosen over one using
> backbone area.
> But I always have opposite result. doesn't Cisco's
> implementation yet
> conform to rfc2328 in this respect?
> 
> Here's from my cisco 2501 router.
> 
> r2#sh ip ospf data
> -------------------------------------------------omitted
>                Type-5 AS External Link States
> 
> Link ID         ADV Router      Age         Seq#      
> Checksum Tag
> 131.108.0.0     192.168.40.3    324         0x80000003
> 0xE930   0
> r2#
> r2#sh ip ospf border
> 
> OSPF Process 10 internal Routing Table
> 
> Codes: i - Intra-area route, I - Inter-area route
> 
> i 192.168.40.3 [74] via 172.16.2.2, Serial0, ABR/ASBR,
> Area 0, SPF 7
> i 192.168.40.3 [1562] via 172.16.30.33, Serial1,
> ABR/ASBR, Area 6, SPF 5
> 
> r2#sh ip route
> -----------------omitted
> O E2 131.108.0.0/16 [110/20] via 172.16.2.2, 00:03:38,
> Serial0
> r2#
> 
> Could somebody explain this to me?
> Thanks in advance.
> 
> 
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