Re: /24 loopback

Hi,

This is true for loopbacks from the same /24 subnet. Just as a clarification
if you use different subnets than there are no restrictions to use the /24
mask on loopbacks used for sham-links.

Regards

Piotr

On Wed, Jun 9, 2010 at 7:22 AM, <ccie_at_reid.it> wrote:

> 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?
> >>
> >>
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Received on Wed Jun 09 2010 - 18:03:39 ART