From: Larry Roberts (groupstudy@american-hero.com)
Date: Thu Jun 30 2005 - 10:01:58 GMT-3
I understand that Tunnels do in fact extend the backbone. I was under
the (false) impression that you couldn't stack or daisy-chain virtual
links because the virtual-link itself didn't truly extend the backbone.
Don't ask me where I got that impression though...
Schulz, Dave wrote:
> If you are addressing the interfaces at both ends of your tunnel and
> putting them in area 0, then you are not violating OSPF. You have to
> remember to do it on both ends of the tunnels (R2 and R7, R2 and R7, R2
> and R9). In this way, you are truly extending OSPF area 0. Hope this
> helps.
>
>
> Dave
>
> -----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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