Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 8 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling
Configuring 802.1Q Tunneling
headers. The packets are encapsulated with the metro tag VLAN ID (set to the access VLAN of the
tunnel port) when they are sent through the service-provider network on an 802.1Q trunk port. The
priority field on the metro tag is set to match the CoS field of the inner tag (or customer tag) by default.
Configuring 802.1Q Tunneling
• Default 802.1Q Tunneling Configuration, page 8-4
• 802.1Q Tunneling Configuration Guidelines, page 8-4
• 802.1Q Tunneling and Other Features, page 8-6
• Configuring an 802.1Q Tunneling Port, page 8-6
Default 802.1Q Tunneling Configuration
By default, 802.1Q tunneling is disabled because the default switchport mode is access. Tagging of
802.1Q native VLAN packets on all 802.1Q trunk ports is also disabled. By default, VLANs on the
router are dot1q tunnel ports.
802.1Q Tunneling Configuration Guidelines
When you configure 802.1Q tunneling, you should always use an asymmetrical link between the
customer device and the edge switch, with the customer device port configured as an 802.1Q trunk port
and the edge switch port configured as a tunnel port.
Assign tunnel ports only to VLANs that are used for tunneling.
The following sections explain the configuration requirements for native VLANs and maximum
transmission units (MTUs).
Native VLANs
When configuring 802.1Q tunneling on an edge switch, you must use 802.1Q trunk ports for sending
packets into the service-provider network. However, packets going through the core of the
service-provider network can be carried through 802.1Q trunks or nontrunking links. When 802.1Q
trunks are used in these core switches, the native VLANs of the 802.1Q trunks must not match any native
VLAN of the nontrunking (tunneling) port on the same switch because traffic on the native VLAN would
not be tagged on the 802.1Q sending trunk port.
See Figure 8-3. VLAN 40 is configured as the native VLAN for the 802.1Q trunk port from Customer X
at the ingress edge switch in the service-provider network (Switch B). Switch A of Customer X sends a
tagged packet on VLAN 30 to the ingress tunnel port of Switch B in the service-provider network, which
belongs to access VLAN 40. Because the access VLAN of the tunnel port (VLAN 40) is the same as the
native VLAN of the edge-switch trunk port (VLAN 40), the metro tag is not added to tagged packets
received from the tunnel port. The packet carries only the VLAN 30 tag through the service-provider
network to the trunk port of the egress-edge switch (Switch C) and is misdirected through the egress
switch tunnel port to Customer Y.