Re: /24 loopback

Hi Garth,

Yes, I had exactly the same thought myself this morning.
Sham-links are useful to solve backdoor issues across an MPLS VPN, just
have a look at both INE and IPExpert blogs. There is an excellent write up
on both of them. I do not believe there is anyway you can use a /24
network in a sham-link for the following reasons: the network has to exist
in a VRF (assuming an MPLS VPN network and PE routers), the network can
NOT be advised in the IGP used across the VRF, and lastly the network must
be advertised with the /32 mask in the vrf address-family. If you look at
the route within the VRF on the other PE you will see a /32 network learnt
via BGP (with either a metric of 200 or 20 depending if the PE's are in
the same BGP AS or not). This is then reachable and a sham-link can be
built using these addresses (/32) as endpoints. If a /24 network is
assigned for the endpoints, then only the /24 network appears as connected
in the local VRF routing table (connected wins by admin distance over bgp
learnt routes). So there is never going to be any connectivity and the
sham-link will not come up.

Tunnels, on the other hand, are more approriate for providing OSPF
connectivity across non-OSPF domains. They have nothing to do with
sham-links

I will be labbing a tunnel scenario tonight for fun :)

regards Andy

> Just off the top of my head, if you wanted to do this couldn't you just
> use
> a GRE tunnel to achieve this?
>
> I'll try lab this up when I have some time later this week.
>
> Cheers,
>
> Garth
>
> On Mon, Jun 7, 2010 at 6:18 PM, Joe Astorino
> <joe_astorino_at_comcast.net>wrote:
>
>> Not according to the documentation. I have tried this myself, and have
>> never got it to come up with a /24
>>
>> Regards,
>> Joe Astorino, CCIE #24347
>>
>> "He not busy being born is busy dying" -- Dylan
>>
>> ----- Original Message -----
>> From: "Abiola Jewoola" <biola_y2k_at_yahoo.com>
>> To: ccielab_at_groupstudy.com
>> Sent: Monday, June 7, 2010 2:22:27 AM GMT -05:00 US/Canada Eastern
>> Subject: /24 loopback
>>
>> Hello GS,
>>
>> Is it possible to configure a Sham-Link with a /24 Loopback address?
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Wed Jun 09 2010 - 13:22:23 ART