Cisco 7604 Configuration Manual page 239

Chapter 17 Configuring IEEE 802.1Q Tunneling
• Spanning-tree BPDU filtering is enabled automatically on tunnel ports.
CDP is automatically disabled on tunnel ports.
•
VLAN Trunk Protocol (VTP) does not work between the following devices:
•
–
–
Note
To configure an EtherChannel as an asymmetrical link, all ports in the EtherChannel must have the
•
same tunneling configuration. Because the Layer 3 packet within the Layer 2 frame cannot be
identified, you must configure the EtherChannel to use MAC-address-based frame distribution.
The following configuration guidelines are required for your Layer 2 protocol tunneling configuration:
On all the service provider edge routers, PortFast BPDU filtering must be enabled on the 802.1Q
•
tunnel ports as follows:
Router(config-if)# spanning-tree bpdufilter enable
Router(config-if)# spanning-tree portfast
Note
At least one VLAN must be available for Native VLAN tagging (vlan dot1q tag native option). If
•
you use all the available VLANs and then try to enable the vlan dot1q tag native option, the option
will not be enabled.
On all the service provider core routers, tag native VLAN egress traffic and drop untagged native
•
VLAN ingress traffic by entering the following command:
Router(config)# vlan dot1q tag native
On all the customer routers, either enable or disable the global vlan dot1q tag native option.
•
Note
The following configuration guidelines are optional for your Layer 2 protocol tunneling configuration:
Because all the BPDUs are being dropped, spanning tree PortFast can be enabled on Layer 2
•
protocol tunnel ports as follows:
Router(config-if)# spanning-tree portfast trunk
If the service provider does not want the customer to see its routers, CDP should be disabled on the
•
802.1Q tunnel port as follows:
Router(config-if)# no cdp enable
OL-4266-08
Devices connected by an asymmetrical link
Devices communicating through a tunnel
VTP works between tunneled devices if Layer 2 protocol tunneling is enabled. See
Chapter 18, "Configuring Layer 2 Protocol Tunneling,"
Spanning-tree BPDU filtering is enabled automatically on tunnel ports.
If this option is enabled on one router and disabled on another router, all traffic is dropped;
all customer routers must have this option configured the same on each router.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
802.1Q Tunneling Configuration Guidelines and Restrictions
for configuration details.
17-5