Cisco WS-C2960S-24PD-L Software Guide - Page 258

How the VMPS Works Chapter 8 Configuring VLANs How the VMPS Works A switch running this software release acts as a client to the VLAN Membership Policy Server (VMPS) and communicates with it through the VLAN Query Protocol (VQP). When the VMPS receives a VQP request from a client switch, it searches its database for a MAC-address-to-VLAN mapping. The server response is based on this mapping and whether or not the server is in secure mode. Secure mode determines whether the server shuts down the port when a VLAN is not allowed on it or just denies the port access to the VLAN. 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 reenabled by using the CLI, Cluster Management software, 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. Dynamic Port VLAN Membership A dynamic (nontrunking) port on the switch can belong to only one VLAN. 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). For more information on possible VMPS responses, see the "How the VMPS Works" section on page 8-36. 8-36 Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide 78-6511-08