Cisco ME 3400 Series, Software Configuration Manual

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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 13 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling
Configuring 802.1Q Tunneling
Configuring 802.1Q Tunneling
• Default 802.1Q Tunneling Configuration, page 13-4
•
802.1Q Tunneling Configuration Guidelines, page 13-4
• 802.1Q Tunneling and Other Features, page 13-5
•
Configuring an 802.1Q Tunneling Port, page 13-6
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
switch are UNI-ENI isolated VLANs.
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.
Configuration requirements for native VLANs and for and maximum transmission units (MTUs) are
explained in these next sections.
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, ISL 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 13-3 . 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.
These are some ways to solve this problem:
•
Use ISL trunks between core switches in the service-provider network. Although customer
interfaces connected to edge switches must be 802.1Q trunks, we recommend using ISL trunks for
connecting switches in the core layer. The Cisco ME switch does not support ISL trunks.
• Use the vlan dot1q tag native global configuration command to configure the edge switch so that
all packets going out an 802.1Q trunk, including the native VLAN, are tagged. If the switch is
configured to tag native VLAN packets on all 802.1Q trunks, the switch accepts untagged packets,
but sends only tagged packets.