Troubleshooting guide

3. Troubleshooting Functional Failures During Operation
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3.6 Layer 2 network communication failures
3.6.1 Layer 2 communication by VLANs is not possible
If Layer 2 communication is not possible when VLANs are used, isolate the cause of the problem
according to the failure analysis method described in the table below.
(1) Checking the VLAN status
Execute the
show vlan command or the show vlan command with the detail parameter to check
the status of the VLAN. The following describes the items that must be checked for each VLAN
type.
(a) Items checked in common for all VLAN types
 Check whether the VLAN is configured correctly on the port.
 Check whether the correct mode is set for the port. If the expected port does not belong to the
default VLAN (VLAN ID 1), check whether:
• A port VLAN other than VLAN ID 1 is specified for the access VLAN or native VLAN.
• The default VLAN is set in
allowed vlan for trunk ports.
• The port is specified as a mirror port.
 Check whether IEEE 802.1X VLAN-based authentication (static), Web authentication (fixed
VLAN mode), or MAC-based authentication is set only for some of the VLANs configured
for trunk ports.
(b) For protocol VLANs
When you are using a protocol VLAN, execute the
show vlan command and make sure the
protocol has been configured correctly.
# show vlan
:
VLAN ID:100 Type:Protocol based Status:Up
Protocol VLAN Information Name:ipv4
EtherType:0800,0806 LLC: Snap-EtherType:
Learning:On Uplink-VLAN: Uplink-Block: Tag-Translation:
:
(c) For MAC VLANs
 When you are using a MAC VLAN, execute the show vlan mac-vlan command and make
sure the MAC addresses allowed for communication that uses the VLAN have been set
correctly. In the example below, the value enclosed in parentheses indicates the functionality
used to register the MAC address.
[Functionality]
static: The MAC address is set in the configuration.
dot1x: The MAC address is set by the IEEE 802.1X functionality.
wa: The MAC address is set by Web authentication.
vaa: The MAC address is set by an authentication VLAN.
# show vlan mac-vlan
:
VLAN ID:100 MAC Counts:4
0012.e200.0001 (static) 0012.e200.00:02 (static)
0012.e200.0003 (static) 0012.e200.00:04 (dot1x)