Can I use a GRE tunnel to solve my problem?

[procopius1980]

Please see the attached file for a topology of the relevant portions of this network.

All but three of the APs at Building B are plugged into Cisco 3650 switches that are also acting as the WLCs.  This allows for local switching of WiFi client traffic.  The WiFi clients are tagged with VLAN 20 and the PCs at Building B are tagged with VLAN 10.  Inter-VLAN routing occurs at the 3560 in Building B.  This is important so that iPads on the WiFi network are switched locally with the PCs in the classroom. I then turn on the mDNS feature on the 3650/WLC so that we can use our PCs as "Apple TVs" via a program called Air Server.  This allows the teacher to project the iPad onto the PC, which is then projected to the SMART Board.

My problem is with the 3 classrooms whose APs plug into a 2960-PS.  These APs are managed by the dedicated WLC-5760 located at Building A.  This means that the teacher PC is using the 3560 in Building B as the default gateway while the wireless traffic is being handled by the 3750 in Building A.  The last time I checked, the WLC 5700 series controllers did not have Flex Connect as a feature.  

Here's my question:  Is there any type of IP tunneling solution I could use to tunnel a particular client or VLAN so that it can be routed at Building A?  I've only played with tunneling from an IPv4/IPv6 standpoint.  Thank you for your time!

[Joseph W. Doherty]

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Posting

It sounds like you're looking to tunnel L2, if so GRE won't help, although something like L2TPv3 might.  Unfortunately it's probably not supported on your devices.

However, as you're working with L2 and L3 switches, you should be able to extend a VLAN to where ever you would like.

[procopius1980]

I did some research and L2TPv3 is only available on high end routers.

Would you be willing to flesh out the other option in more detail?  My understanding is that you cannot extend a VLAN beyond a Layer 3 boundary. Thanks!

[procopius1980]

Ok - looks like there is now what is called Converged Mode within the 5700 and 3850/3650 series controllers.  I am going to try posting this scenario with the wireless group, although please feel free to share any more information regarding your other suggestion.

[Jon Marshall · Accepted solution]

What is the connection between the switches in Building A and B ?

If it is a trunk then simply move the SVI for the specific vlan to the Building A switch.

If it is a routed link using ports with IP addresses configured on them then you could -

1) convert the link to a trunk

2) create a new dedicated vlan with no end hosts in it and have an SVI for that vlan on both switches. This vlan in effect emulates your previous P2P link and you route all traffic except the vlan you want to extend.

You would allow only the new dedicated vlan and the vlan you are extending on that trunk link, no other vlans.

3) move the SVI for the vlan you are extending to the Building A switch

This should work fine but it does mean if you are currently running a routed connection STP between those switches so you would need to take that into account.

Might be an option for you if the Wireless people don't come up with anything.

Jon

[procopius1980]

Jon and Joseph,

I apologize for not making it clear that I knew I could fix the problem by converting the link to a trunk.  I was looking for a unique solution because I want to avoid doing this if possible.  I like having the two buildings broken up from a design standpoint, but my network is certainly small enough to let the 3750 at Building A handle inter-VLAN-routing for both campuses.  

I am going to check out the wireless forum and see if they have an alternative solution.  Thank you both a great deal for taking the time to look over this with me.

[Joseph W. Doherty · Accepted solution]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

You're correct, you cannot extend L2 across L3 unless you use some kind of encapsulation technology, for example, the already mentioned L2TPv3 or pseudo-wire over MPLS, etc.

However, what I have in mind for extending a VLAN means converting a routed p2p link to a L2 trunk link (I'm assuming the equipment, e.g. L3 switches, can support this). Across the trunk, you can extend your VLAN(s).  For the routers, you can dedicate a new VLAN, across just the trunk, that takes the place of the former p2p.  I.e. so you can do both L2 and L3 across the same physical link.

[edit]

I didn't see Jon's post until after I posted above, but he's explaining, in more detail, what I had in mind.