DOT1Q Tunnelling

This feature allows a user trunk to be encapsulated in a tagged vlan across a service provider cloud. The switchport configuration is fairly straightforward.

1) Select a vlan that will be used to encapsulated and trunk the user traffic
2) Set up the service provider edge switch ports as dot1q tunnel ports



R4 --------- SW3 ----------------- SW4 ---------- R5


SW3
vlan 500

interface fastethernet 0/23
switchport access vlan 500
switchport mode dot1q-tunnel
l2protocol-tunnel cdp
no cdp enable


SW4
vlan 500

interface fastethernet 0/23
switchport access vlan 500
switchport mode dot1q-tunnel
l2protocol-tunnel cdp
no cdp enable

The user router ports are set as trunk ports e.g.

R4#s run begin interface Fast
interface FastEthernet0/0
no ip address
duplex full
!
interface FastEthernet0/0.4
encapsulation dot1Q 4
ip address 191.1.4.4 255.255.255.0
!
interface FastEthernet0/0.40
encapsulation dot1Q 40
ip address 191.1.40.4 255.255.255.0
!
interface FastEthernet0/0.45
encapsulation dot1Q 45
ip address 191.1.45.4 255.255.255.0
!
interface FastEthernet0/0.49
encapsulation dot1Q 49
ip address 191.1.49.4 255.255.255.0


R5#s run beg interface Fas
interface FastEthernet0/0
duplex full
!
interface FastEthernet0/0.45
encapsulation dot1Q 45
ip address 191.1.45.5 255.255.255.0
!
interface FastEthernet0/0.50
encapsulation dot1Q 50
ip address 191.1.50.5 255.255.255.0
!
interface FastEthernet0/0.59
encapsulation dot1Q 59
ip address 191.1.59.5 255.255.255.0!

N.B. 2 desirable commands when implementing a dot1q tunnel...
system mtu 1504 - ensures the exra 4 byte dot1q header is accomodated
vlan dot1q tag native - ensures there is no chance of confusion between customer and service provider untagged vlans.

N.B.B Having now revisited this blog some 5 months later i realise one assumption made here!! Of course VLAN 500 must be trunked between the SP switches!!