Here is the topology.
VLAN 10 in a Customer Site in California (SW1) needs to be extended to a Customer Site in Illinois (SW4).
First we need to configure the customer equipment to put the interface facing the service provider on VLAN 10.
SW1#sh run int fa1/1 interface FastEthernet1/1 description SW1 to SP1 switchport access vlan 10 end SW1#sh run int vlan 10 interface vlan10 ip address 10.10.10.1 255.255.255.0 end
Next we need to get SP1 interface facing the customer in a q-in-q mode and assign a metro-tag. In this case I assigned metro-tag 510.
SP1#sh run int fa1/1 interface FastEthernet1/1 description SW1 to SW4 dot1q switchport access vlan 510 !!VLAN 510 above is commonly referred to as metro-tag or customer tag. switchport mode dot1q-tunnel !!Notice that we also tunnel cdp, stp, and vtp as well. !!Normally they would not be by default l2protocol-tunnel cdp l2protocol-tunnel stp l2protocol-tunnel vtp no cdp enable end
Now we need to configure the interfaces between the Service Providers which is just a basic trunk.
SP1#sh run int fa1/2 interface FastEthernet1/2 description connected to SP2 switchport trunk encapsulation dot1q switchport mode trunk end
SP2#sh run int fa1/2 interface FastEthernet1/1 description connected to SP1 switchport trunk encapsulation dot1q switchport mode trunk end
The interface on SP2 facing the customer side is assigned the same metro-tag of 510.
SP2#sh run int fa1/3 interface FastEthernet1/3 description SW4 to SW1 dot1q switchport access vlan 510 switchport mode dot1q-tunnel l2protocol-tunnel cdp l2protocol-tunnel stp l2protocol-tunnel vtp no cdp enable end
We need to configure the customer equipment to put the interface facing the service provider on VLAN 10.
SW4#sh run int fa1/3 interface FastEthernet1/3 description connected to SP2 switchport access vlan 10 end SW#sh run int vlan 10 interface vlan10 ip add 10.10.10.4 255.255.255.0 end
Let's see what happens when we ping from SW1 to SW4.
SW1#ping 10.10.10.4 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.10.4, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/10/12 ms SW1#
Let's see what CDP shows.
SW1#show cdp neighbors Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone Device ID Local Intrfce Holdtme Capability Platform Port ID SW4 Fas 1/1 142 R 3550 Fas 1/3 SW1#
As you can see it appears as though SW4 is connected directly to SW1. What is really happening is that VLAN 10 traffic is double tagged with VLAN 510. In other words VLAN 10 is encapsulated in VLAN 510 and sent across to SP2 hence the q-in-q tunneling.
Side note -- You will have to set the system mtu greater than 1500 on the SP1 and SP2 switches which does require a reboot to take effect. In the Cisco 3750s that I used the command to increase the system mtu is "system mtu 1546".
Many more articles to come so stay tuned.
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