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Troubleshooting 802.1Q Troubleshooting 802.1Q
OmniSwitch Troubleshooting Guide September 2005 page 8-3
Default VLAN Traffic
If traffic that should be in the default VLAN is not passing properly, first verify that the default VLAN is
set correctly, as see above. Also note the switch can be configured to either accept or deny untagged pack-
ets.
When enabling a port on the OmniSwitch 7700/7800/8800 to accept tagged traffic, you can specify
whether only 802.1Q tagged traffic is allowed on the port (deny all bridged traffic), or whether the port
accepts both tagged and untagged traffic.
OmniSwitch 7700/7800/8800 has a feature that enables it to accept all data on a bridged VLAN or deny all
of the bridged traffic.
The vlan 802.1q frame type all CLI command allows all the bridged traffic to be accepted on a tagged
link. When using an OmniSwitch 7700/7800/8800 with an OmniSwitch or Omni Switch/Router where
default VLAN needs to be bridged, this command should be set to all so that the bridged traffic can be
accepted by the OmniSwitch 7700/7800/8800 in addition to the tagged traffic.
For devices that cannot bridge on the tagged link, e.g. an OmniCore, the OmniSwitch 7700/7800/8800 can
be configured to accept only tagged traffic and ignore all the bridged traffic using the command. If frame
type is set to tagged, all non tagged traffic will be dropped.
The vlan 802.1q frame type tagged CLI command will deny all of the bridged traffic. Bridged traffic is
classified as traffic without a VLAN Identification (VID). Any packet without VID will be discarded.
Only tagged traffic will be accepted.
To verify if the port will receive untagged frames use the show 802.1q CLI command as shown below.
Note the Acceptable Frame Type field, Any Frame Type indicates this port will receive untagged
frames as well as tagged frames.
-> show 802.1q 5/24
Acceptable Frame Type : Any Frame Type
Force Tag Internal : on
Tagged VLANS Internal Description
-------------+------------------------------------------+
30 TAG PORT 5/24 VLAN 30
40 TAG PORT 5/24 VLAN 40
50 TAG PORT 5/24 VLAN 50
Tagged Packet on an Untagged Port
If a tagged packet comes on an untagged or group mobility port (i.e., the vlan 802.1q CLI command has
not been used), then it can be classified in a VLAN other than the VLAN it currently belongs to. If this
classified VLAN (i.e., different then the packet tag) is now tagged on the egress side, then there are two
possible options.
One option is to carry the original tag of the packet and other option is to replace it with the classified
VLAN as the tag. If the force tag internal is disabled (on), then the tag is not replaced with the classified
VLAN. If the force tag internal is enabled (off), then the tag is replaced with the classified VLAN as the
tag.
Please note the above output of show 802.1Q CLI command shown in “Default VLAN Traffic” on
page 8-3.