Cisco Systems 3560 Manual De Usuario
16-5
Catalyst 3560 Switch Software Configuration Guide
OL-8553-06
Chapter 16 Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
Configuring IEEE 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 IEEE 802.1Q trunks, we recommend using ISL trunks
for connecting switches in the core layer.
interfaces connected to edge switches must be IEEE 802.1Q trunks, we recommend using ISL trunks
for connecting switches in the core layer.
•
Use the vlan dot1q tag native global configuration command to configure the edge switch so that
all packets going out an IEEE 802.1Q trunk, including the native VLAN, are tagged. If the switch
is configured to tag native VLAN packets on all IEEE 802.1Q trunks, the switch accepts untagged
packets, but sends only tagged packets.
all packets going out an IEEE 802.1Q trunk, including the native VLAN, are tagged. If the switch
is configured to tag native VLAN packets on all IEEE 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.
range. For example, if the trunk port carries traffic of VLANs 100 to 200, assign the native VLAN
a number outside that range.
Figure 16-3
Potential Problem with IEEE 802.1Q Tunneling and Native VLANs
System MTU
The default system MTU for traffic on the switch is 1500 bytes. You can configure Fast Ethernet ports
to support frames larger than 1500 bytes by using the system mtu global configuration command. You
can configure Gigabit Ethernet ports to support frames larger than 1500 bytes by using the system mtu
jumbo global configuration command. Because the IEEE 802.1Q tunneling feature increases the frame
size by 4 bytes when the metro tag is added, you must configure all switches in the service-provider
network to be able to process maximum frames by increasing the switch system MTU size to at least
1504 bytes. The maximum allowable system MTU for Gigabit Ethernet interfaces is 9000 bytes; the
maximum system MTU for Fast Ethernet interfaces is 1998 bytes.
to support frames larger than 1500 bytes by using the system mtu global configuration command. You
can configure Gigabit Ethernet ports to support frames larger than 1500 bytes by using the system mtu
jumbo global configuration command. Because the IEEE 802.1Q tunneling feature increases the frame
size by 4 bytes when the metro tag is added, you must configure all switches in the service-provider
network to be able to process maximum frames by increasing the switch system MTU size to at least
1504 bytes. The maximum allowable system MTU for Gigabit Ethernet interfaces is 9000 bytes; the
maximum system MTU for Fast Ethernet interfaces is 1998 bytes.
802.1Q
trunk port
VLANs 30-40
Native VLAN 40
trunk port
VLANs 30-40
Native VLAN 40
Tunnel port
Access VLAN 30
Tunnel port
Service
provider
Tag not added
for VLAN 40
Tag
removed
VLANs 5-50
Switch D
Customer X
VLANs 30-40
Native VLAN 40
Switch B
Switch C
Q
Q
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
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
Access VLAN 40
Packet tagged
for VLAN 30
VLAN 40