L2 over GRE on Catalyst Switches

Andres Franco · ‎06-29-2015

Hi Community,

Suppose the following scenario:

(SVI Vlan X )--- 3750----------L3 link ------6509--------L3 link-------6513------(L2 only Vlan X)

¿Can I use L2 over GRE in order to tunnel VlanX so that I can have one SVI on one end and layer 2 Vlan on the other? What other solution is possible? I have read about L2TP (pseudowire) but for some reason xconnect command is not available on 3750 switch. Thanks in advance for your help.

Joseph W. Doherty · ‎06-30-2015

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Posting

To my knowledge, GRE will not support L2. For a tunneling protocol, you need something like L2TPv3, but as you've discovered, basic LAN switches, like the 3750 don't support it (or course, they don't support GRE tunnel end points either).

From what you've posted, you can extend your VLAN by trunking across the L3 switches. The existing L3 links can still support a logical p2p on a dedicated VLAN across the trunk.

Andres Franco · ‎06-30-2015

Hi Joseph!

Thanks for your reply.

How could that be?. I´ve never mixed a layer 2 trunk over a SVI. Could you please give an example o refer me to a link?

Regards,

Joseph W. Doherty · ‎07-01-2015

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

Your 3750 has something like:

interface GigabitEthernet1/1/1
no switchport
ip address 192.168.1.2 255.255.255.254

Your 6509 something like:

interface GigabitEthernet1/1
ip address 192.168.1.3 255.255.255.254
interface GigabitEthernet1/2
ip address 192.168.1.4 255.255.255.254

Your 6513 something like:

interface GigabitEthernet1/1
ip address 192.168.1.5 255.255.255.254

You convert the above ports to trunk ports and move the IP address to a new VLAN/SVI.

Assuming the VLAN you wish to extend is 10, e.g.

Your 3750:

vlan 901
name p2p_1st_hop
interface GigabitEthernet1/1/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 10,901
interface vlan 901
ip address 192.168.1.2 255.255.255.254

Your 6509:

vlan 901
name p2p_1st_hop
vlan 902
name p2p_2nd_hop
interface GigabitEthernet1/1
switchport
switchport mode trunk
switchport trunk allowed vlan 10,901
interface GigabitEthernet1/2
switchport
switchport mode trunk
switchport trunk allowed vlan 10,902
interface vlan 901
ip address 192.168.1.3 255.255.255.254
interface vlan 902
ip address 192.168.1.4 255.255.255.254

Your 6513:

vlan 902
name p2p_2nd_hop
interface GigabitEthernet1/1
switchport
switchport mode trunk
switchport trunk allowed vlan 10,902
interface vlan 902
ip address 192.168.1.5 255.255.255.254