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
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.
Note The Cisco MWR 2941 router 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.
• Ensure that the native VLAN ID on the edge-switch trunk port is not within the customer VLAN
range. For example, if the trunk port carries traffic of VLANs 100 to 200, assign the native VLAN
a number outside that range.
Figure 8-3 Potential Problem with 802.1Q Tunneling and Native VLANs
System MTU
The default MTU size for Gigabit Ethernet ports is 9216 bytes and is a fixed value. Release 15.1(1)MR
does not support the system mtu or system mtu jumbo command.
802.1Q
trunk port
VLANs 30-40
Native VLAN 40
Tunnel port
Access VLAN 30
Tunnel port
Service
provider
Tag not added
for VLAN 40
Ta g
removed
VLANs 5-50
Switch D
Customer X
VLANs 30-40
Native VLAN 40
Switch B Switch C
QQ
Switch E
Customer Y
Switch A
Customer X
Native
VLAN 40
101820
Trunk
Asymmetric link
Correct path for traffic
Incorrect path for traffic due to
misconfiguration of native VLAN
by sending port on Switch B
Q = 802.1Q trunk ports
Tunnel port
Access VLAN 40
Packet tagged
for VLAN 30
VLAN 40