Dynamic Port Vlan Membership; Vmps Database Configuration File - Cisco Catalyst 2950 Software Configuration Manual

Chapter 13 Configuring VLANs

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 VMPS server. The file contains VMPS information,
such as the domain name, the fallback VLAN name, and the MAC-address-to-VLAN mapping. The
Catalyst 2950 switch cannot act as the VMPS, but you can use a Catalyst 5000 or Catalyst 6000 series
switch as the VMPS.
You can configure a fallback VLAN name. If you connect a device with a MAC address that is not in the
database, the VMPS sends the fallback VLAN name to the client. If you do not configure a fallback
VLAN and the MAC address does not exist in the database, the VMPS sends an access-denied response.
If the VMPS is in secure mode, it sends a port-shutdown response.
Whenever port names are used in the VMPS database configuration file, the server must use the switch
convention for naming ports. For example, Fa0/4 is fixed Fast Ethernet port number 4. If the switch is a
cluster member, the command switch adds the name of the switch before the type. For example,
es3%Fa0/4 refers to fixed Fast Ethernet port 4 on member switch 3. When port names are required, these
naming conventions must be followed in the VMPS database configuration file when it is configured to
support a cluster.
This example shows a example of a VMPS database configuration file as it appears on a Catalyst 6000
series switch. The file has these characteristics:
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78-11380-04
The security mode is open.
The default is used for the fallback VLAN.
MAC address-to-VLAN name mappings—The MAC address of each host and the VLAN to which
each host belongs is defined.
Port groups are defined.
VLAN groups are defined.
VLAN port policies are defined for the ports associated with restricted VLANs.
Catalyst 2950 Desktop Switch Software Configuration Guide
Configuring VMPS
13-31