Troubleshooting

Unusual Network Activity

VLAN-Related Problems

Monitor Port. When using the monitor port in a multiple VLAN environ- ment, it can be useful to know how broadcast, multicast, and unicast traffic is tagged. The following table describes the tagging to expect.

 

Within Same

Within Same

Outside of

Outside of

 

Tagged VLAN

Untagged VLAN

Tagged Monitor

Untagged Monitor

 

as Monitor Port

as Monitor Port

Port VLAN

Port VLAN

 

 

 

 

 

Broadcast

Tagged

Untagged

Untagged

Untagged

Multicast

Tagged

Untagged

Untagged

Untagged

Unicast Flood

Tagged

Untagged

Untagged

Untagged

Unicast Not

Untagged

Untagged

Untagged

Untagged

to Monitor

 

 

 

 

Port

 

 

 

 

Unicast to

Tagged

Untagged

N/A—Dropped

N/A—Dropped

Monitor Port

 

 

 

 

 

 

 

 

 

None of the devices assigned to one or more VLANs on an 802.1Q-

compliant switch are being recognized. If multiple VLANs are being used on ports connecting 802.1Q-compliant devices, inconsistent VLAN IDs may have been assigned to one or more VLANs. For a given VLAN, the same VLAN ID must be used on all connected 802.1Q-compliant devices.

Link Configured for Multiple VLANs Does Not Support Traffic for One

or More VLANs. One or more VLANs may not be properly configured as “Tagged” or “Untagged”. A VLAN assigned to a port connecting two 802.1Q- compliant devices must be configured the same on both ports. For example, VLAN_1 and VLAN_2 use the same link between switch “X” and switch “Y”.

 

 

 

 

Link supporting VLAN_1

 

 

 

 

 

Switch “X”

 

and VLAN_2

 

Switch “Y”

 

 

 

 

 

 

 

 

 

 

 

 

Port X-3

 

 

 

Port Y- 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VLAN Port Assignment

 

VLAN Port Assignment

Port

VLAN_1 VLAN_2

 

Port

VLAN_1

VLAN_2

X-3

Untagged Tagged

 

Y-7

Untagged

Tagged

Figure 11-1. Example of Correct VLAN Port Assignments on a Link

Troubleshooting

11-9