From: Ronnie Royston (RonnieR@xxxxxxxxxxxxxxxxx)
Date: Thu Feb 15 2001 - 20:16:58 GMT-3
1. Shortest path to area 0
2. Shortest path across area 0 w/out going through non-zero area
3. Shortest path to destination w/out going through area 0
i.e., packet sent to area 0 first, then packet sent through area 0, then
packet sent to destination without going back through area 0.
-----Original Message-----
From: Damien [mailto:damien@clara.co.uk]
Sent: Thursday, February 15, 2001 8:09 AM
To: ccielab@groupstudy.com
Subject: OSPF Guru's
Just thought I would drop this in as I have not had time to try it in =
the Lab........
If you have your typical Virtual Link set up....for a disconnected Area =
i.e.......using another non Backbone Area as a Transit to the Area =
0..........
| |
| |
Area 2 | Area 1 | Area 0
| |
so you have a virtual link between Area 2 & 1's ABR and Area 1&0's ABR.
If traffic from Area 2 is destined to Area 1 what path will the packet =
take. From what I understand in RFC 2328 Moy, the Virtual link enables =
Transit Traffic to be forwarded through Area 1, but the actual path the =
transit data traffic takes does not follow the virtual link. In other =
words, virtual links allow transit traffic to be forwarded through an =
area, but do not dictate the precise path that the traffic will take.
If you read Section 16.3 of the RFC, it seems to indicate that the =
Traffic, based on the way the SPF is calculated will go straight from =
Area 2 into Area 1. The common misconception being you have to Traverse =
through Area 1 and then to the Virtual link next hop i.e. Area 0 before =
you get to the Inter-Area route, when it appears this is not the =
case.....
Can anyone who has confirmed this let me know, or knows of any other =
Document that details this other than the RFC .....from all the people =
(CCIE's) I have have asked some have confirmed......although with =
reservation that they think this is the case.....?
Damien
CCIE#6634
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