From: Scott Vermillion (scott_ccie_list@it-ag.com)
Date: Mon Oct 29 2007 - 16:54:04 ART
Hey Narbik,
Don't educate me too much before your upcoming bootcamp! But I couldn't
really decipher the context of this:
"OSPF area capability transit is enabled by default, allowing the OSPF Area
Border Router to install better-cost routes to the backbone area through the
transit area instead of the virtual links. If you want to retain a traffic
pattern through the virtual-link path, you can disable capability transit by
entering the no capability transit command. If paths through the transit
area are discovered, they are most likely to be more optimal paths, or at
least equal to, the virtual-link path. To reenable capability transit, enter
the capability transit command."
Have I ever mentioned that virtual links are my least favorite aspect of
OSPF?!
I just happen to have an active OSPF component in the lab I'm currently
working if anyone has suggestions as to how to see this in action (and come
to understand how it applies to the discussion at hand - I'm near 100% sure
Narbik is suggesting I'm incorrect in my below statement, but it's not
exactly jumping out at me).
Regards,
Scott
From: Narbik Kocharians [mailto:narbikk@gmail.com]
Sent: Monday, October 29, 2007 1:38 PM
To: Scott Vermillion
Cc: CCIEin2006; Cisco certification
Subject: Re: Why must all areas connect to Area 0?
Look at the "capability transit" command
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hirp_r
/rte_osph.htm#wp999437
On 10/29/07, Scott Vermillion <scott_ccie_list@it-ag.com> wrote:
It must flow to Area 0. You cannot build a virtual link directly between
Areas 1 and 2; all virtual links either connect two pieces of Area0 or they
connect a non-0 area to Area 0. In other words, all virtual links involve
Area 0!
-----Original Message-----
From: nobody@groupstudy.com [mailto: nobody@groupstudy.com
<mailto:nobody@groupstudy.com> ] On Behalf Of
CCIEin2006
Sent: Monday, October 29, 2007 12:42 PM
To: Cisco certification
Subject: Re: Why must all areas connect to Area 0?
So in this scenario
Area1-Area2
\ /
Area0
Area 1 and 2 are directly connected. Would the data need to flow to area0 or
can the traffic flow directly?
What if we configured a virtual link between them?
On 10/29/07, CCIEin2006 < ciscocciein2006@gmail.com> wrote:
>
> Hi folks,
>
> I was reading over Jeff Doyle's blog and came across his favorite
> interview question:
> Why does OSPF require all traffic between non-backbone areas to pass
> through a backbone area (area 0)?
>
> Answer:
> Because inter-area OSPF is distance vector, it is vulnerable to routing
> loops. It avoids loops by mandating a loop-free inter-area topology, in
> which traffic from one area can only reach another area through area 0.
>
> Can someone elaborate on that answer a little bit? Exactly how does having
> a connection to Area0 prevent routing loops? Is it similar to spanning
tree
> in the area 0 is the root of the spanning tree?
>
> Also this answer does not take into consideration redistribution from
> another routing protocol right?
>
> Thank You
>
> Here is the article:
> http://www.networkworld.com/community/node/19293
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