From: Scott Morris (swm@emanon.com)
Date: Sun Apr 23 2006 - 17:10:14 GMT-3
I did the same thing you did... Went "wow, never thought about that!", and
also perused the RFC briefly (short enough not to be put to sleep).
I would agree with your assessment on this, in that a virtual link is not
designed to transit traffic per se, but designed as a method of moving
traffic through a "transit area". Interfaces that move traffic have
bandwidth and costs associated with them. A virtual link is not such an
interface.
But that was a rather good question, and definitely one that made me think!
;)
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Reinhold Fischer
Sent: Sunday, April 23, 2006 5:59 AM
To: Victor Cappuccio
Cc: ccIE LAB
Subject: Re: OSPF Virtual Link Cost
Hi Victor,
this is really an interesting question that i never thought about.
The following is just my understanding and i could be wrong:
The virtual link is not like a tunnel where packets are forwarded through.
It is just a definition, that (simplified) says that two not directly
connected routers should exchange ospf information by means of ip unicast
packets. That packets follow a certain way through the transit area
according to the ospf metrics of the links in that transit area. The metric
that you see on the virtual link and that is visible to the backbone area is
the metric of this best way through the transit area.
The separate link metrics and details of the transit area are not known to
the backbone area.
I think there is no reason to be able to change the cost of the VL directly.
The VL is just a simplified representation of the cost to go through the
transit area used by the SPF calculation of the backbone area.
Anyone with a better explanation? I've read rfc2328 and Routing TCPIP
Vol1 but found no good explanation. Eventually the John Moy OSPF book has a
better information, but i do not have this book...
regards
reinhold
On Sat, Apr 22, 2006 at 04:52:15PM -0400, Victor Cappuccio wrote:
> Hello All,
>
> Does anyone know how to modify the OSPF Virtual Link Cost?
> I been searching in cisco/google/router but with no luck (seems to me
> logic to modify a Cost to a Virtual Link), and yes we can lower the
> cost of other interfaces, but why not with the VL?
>
> Thanks
> Victor.
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