IEEE 802.1Q Tunneling and Incompatibilities
AlthoughIEEE 802.1Q tunneling works well for Layer 2packet switching, there are incompatibilities between
someLayer 2 features and Layer 3 switching.
•Atunnel port cannot be a routed port.
•IProuting is not supported on a VLAN that includes IEEE 802.1Q ports. Packets received from a tunnel
portare forwarded based only on Layer 2 information. If routing is enabled on a switch virtual interface
(SVI)that includes tunnel ports, untagged IP packets received from the tunnel port are recognized and
routedby the switch. Customers can access the Internet through its native VLAN. If this access is not
needed,you should not configure SVIs on VLANs that include tunnel ports.
•Fallbackbridging is not supported on tunnel ports. Because all IEEE 802.1Q-tagged packets received
froma tunnel port are treated as non-IP packets, if fallback bridging is enabled on VLANs that have
tunnelports configured, IP packets would be improperly bridged across VLANs. Therefore, you must
notenable fallback bridging on VLANs with tunnel ports.
•Tunnelports do not support IP access control lists (ACLs).
•Layer3 quality of service (QoS) ACLs and other QoS features related to Layer 3 information are not
supportedon tunnel ports. MAC-based QoS is supported on tunnel ports.
•EtherChannelport groups are compatible with tunnel ports as long as the IEEE 802.1Q configuration
isconsistent within an EtherChannel port group.
•PortAggregation Protocol (PAgP), Link Aggregation Control Protocol (LACP), and UniDirectional
LinkDetection (UDLD) are supported on IEEE 802.1Q tunnel ports.
•DynamicTrunking Protocol (DTP) is not compatible with IEEE 802.1Q tunneling because you must
manuallyconfigure asymmetric links with tunnel ports and trunk ports.
•VLANTrunking Protocol (VTP) does not work between devices that are connected by an asymmetrical
linkor devices that communicate through a tunnel.
•Loopbackdetection is supported on IEEE 802.1Q tunnel ports.
•Whena port is configured as an IEEE 802.1Q tunnel port, spanning-tree bridge protocol data unit (BPDU)
filteringis automatically enabled on the interface. Cisco Discovery Protocol (CDP) and the Layer Link
DiscoveryProtocol (LLDP) are automatically disabled on the interface.
Related Topics
Configuringan IEEE 802.1Q Tunneling Port, on page 133
Example:Configuring an IEEE 802.1Q Tunneling Port, on page 143
Layer 2 Protocol Tunneling
Thefollowing are configuration guidelines and operating characteristics of Layer 2 protocol tunneling:
•Theswitch supports tunneling of CDP, STP, including multiple STP (MSTP), and VTP.Protocol
tunnelingis disabled by default but can be enabled for the individual protocols on IEEE 802.1Q tunnel
portsor access ports.
Catalyst 2960-XR Switch VLAN Configuration Guide, Cisco IOS Release 15.0(2)EX1
122 OL-29440-01
Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
IEEE 802.1Q Tunneling and Incompatibilities