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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 16 Configuring VLANs
Configuring VMPS
In response to a request, the VMPS takes one of these actions:
• If the assigned VLAN is restricted to a group of ports, the VMPS verifies the requesting port against
this group and responds as follows:
–
If the VLAN is allowed on the port, the VMPS sends the VLAN name to the client in response.
–
If the VLAN is not allowed on the port and the VMPS is not in secure mode, the VMPS sends
an access-denied response.
–
If the VLAN is not allowed on the port and the VMPS is in secure mode, the VMPS sends a
port-shutdown response.
• If the VLAN in the database does not match the current VLAN on the port and active hosts exist on
the port, the VMPS sends an access-denied or a port-shutdown response, depending on the secure
mode of the VMPS.
If the switch receives an access-denied response from the VMPS, it continues to block traffic from the
MAC address to or from the port. The switch continues to monitor the packets directed to the port and
sends a query to the VMPS when it identifies a new address. If the switch receives a port-shutdown
response from the VMPS, it disables the port. The port must be manually re-enabled by using the device
manager, CLI, , or SNMP.
You can also use an explicit entry in the configuration table to deny access to specific MAC addresses
for security reasons. If you enter the none keyword for the VLAN name, the VMPS sends an
access-denied or port-shutdown response, depending on the VMPS secure mode setting.
Dynamic Port VLAN Membership
A dynamic (nontrunking) port on the switch can belong to only one VLAN, with a VLAN ID from 1 to
1005. When the link comes up, the switch does not forward traffic to or from this port until the VMPS
provides the VLAN assignment. The VMPS receives the source MAC address from the first packet of a
new host connected to the dynamic port and attempts to match the MAC address to a VLAN in the VMPS
database.
If there is a match, the VMPS sends the VLAN number for that port. If the client switch was not
previously configured, it uses the domain name from the first VTP packet it receives on its trunk port
from the VMPS. If the client switch was previously configured, it includes its domain name in the query
packet to the VMPS to obtain its VLAN number. The VMPS verifies that the domain name in the packet
matches its own domain name before accepting the request and responds to the client with the assigned
VLAN number for the client. If there is no match, the VMPS either denies the request or shuts down the
port (depending on the VMPS secure mode setting).
Multiple hosts (MAC addresses) can be active on a dynamic port if they are all in the same VLAN;
however, the VMPS shuts down a dynamic port if more than 20 hosts are active on the port.
If the link goes down on a dynamic port, the port returns to an isolated state and does not belong to a
VLAN. Any hosts that come online through the port are checked again through the VQP with the VMPS
before the port is assigned to a VLAN.
VMPS Database Configuration File
The VMPS contains a database configuration file that you create. This ASCII text file is stored on a
switch-accessible TFTP server that functions as a server for VMPS. The file contains VMPS
information, such as the domain name, the fallback VLAN name, and the MAC-address-to-VLAN
mapping. The switch cannot act as the VMPS, but you can use a Catalyst 5000 or Catalyst 6000 series
switch as the VMPS.