From: Larry Roberts (groupstudy@american-hero.com)
Date: Thu Jun 30 2005 - 09:56:50 GMT-3
Thanks Scott!
I'm not sure why I was thinking the way I was, but the clarification is
appreciated.
As a side note, I continued playing around last night and discovered
that I would see the interface under a "show ip ospf". It was something
along the lines of "Interfaces in the backbone" I don't have access to
routers at the moment to give the exact message.
Scott Morris wrote:
> 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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