From: Scott Morris (swm@emanon.com)
Date: Thu Jun 30 2005 - 03:11:14 GMT-3
A virtual link DOES indeed extend area 0 out. I'm not sure about it showing
up as an interface in "sh ip o i" but it will show up with "sh ip o v" just
fine and you'll see the authentication stuff happening as it needs to as
Area 0.
So with nested VL configurations, each time you use it, you'll be bringing
area 0 out further into your network one hop at a time.
HTH,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Larry Roberts
Sent: Thursday, June 30, 2005 12:28 AM
To: Gustavo Novais
Cc: ccielab@groupstudy.com
Subject: Re: OSPF Virtual Link and GRE tunnel.
Somebody please correct me if Im wrong on my understanding of Virtual-links,
but I believe the virtual link configuration mentioned below is invalid.
I was under the understanding that Virtual links require that one router be
an ABR to area 0 (R2). This virtual link provides backbone connectivity to
area 0 for the ABR (R5) but it doesn't *extend* the backbone to R5 ( R5
doesn't have an interface in Area 0). When you create your second virtual
link from R5 to R7, neither of these routers have an interface in Area 0.
If you do a "show ip ospf interface" on R5, you will see that none of the
interfaces are listed as in area 0. While this configuration seems to work
fine, It appears to me that it is in violation of OSPF configuration
guidelines.
Can anyone correct my understanding on this?
Gustavo Novais wrote:
> Apparently I had a dumb config problem on R7... Duhhh... It's working
> now.
> Either way, any way how to solve recursive routing situation I
> presented?
> Thanks
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Gustavo Novais
> Sent: quarta-feira, 29 de Junho de 2005 19:33
> To: ccielab@groupstudy.com
> Subject: OSPF Virtual Link and GRE tunnel.
>
> Hello group
>
> I have a topology like this.
>
> Area0--(R2)---Area25---(R5)---Area57----(R7)----Area78----(R9)
>
> It showed up on a exercise in order to test Virtual-links etc.
> I did it using vlink between R5 and R2 for area 57 reachability and a
> vlink between R7 and R5 for area 78 reachability.
>
> But I'd like to try the same topology using GRE tunnel between R7 and
> R2.
> If I extend Area 0 onto interface tunnel on R7, I get recursive
> routing and the tunnel goes down. (OSPF will prefer intra area routes
> vs extra area routes, so the preferred path to the tunnel destination
> is through the tunnel itself, which shuts it down.
>
> If I extend area 78 to R2 Tunnel, apparently all is well, but the
> problem is that R5 starts complaining that Received invalid packet:
> mismatch area ID, from backbone area must be virtual-link but not
> found from 150.50.57.7, Ethernet0/0, even now that area 78 is
> connected directly to area 0, and area 57 still has its vlink on R5 to
Area 0.
>
> Any ideas why is the router R5 showing this behaviour? Any suggestions
> how to correct it?
>
> Thanks
>
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