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Catalyst 3750 MetroSwitch Software Configuration Guide
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Chapter 10 Configuring VLANs
Configuring VMPS
Dynamic-Access Port VLAN Membership
A dynamic-access port can belong to only one VLAN with an ID from 1 to 4094. 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-access 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-access port if they are all in the same
VLAN; however, the VMPS shuts down a dynamic-access port if more than 20 hosts are active on the
port.
If the link goes down on a dynamic-access 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.
Dynamic-access ports can be used for direct host connections, or they can connect to a network. A
maximum of 20 MAC addresses are allowed per port on the switch. A dynamic-access port can belong
to only one VLAN at a time, but the VLAN can change over time, depending on the MAC addresses seen.
Default VMPS Client Configuration
Table 10-7 shows the default VMPS and dynamic-access port configuration on client switches.
VMPS Configuration Guidelines
These guidelines and restrictions apply to dynamic-access port VLAN membership:
• You should configure the VMPS before you configure ports as dynamic-access ports.
• When you configure a port as a dynamic-access port, the spanning-tree Port Fast feature is
automatically enabled for that port. The Port Fast mode accelerates the process of bringing the port
into the forwarding state.
• 802.1x ports cannot be configured as dynamic-access ports. If you try to enable 802.1x on a
dynamic-access (VQP) port, an error message appears, and 802.1x is not enabled. If you try to
change an 802.1x-enabled port to dynamic VLAN assignment, an error message appears, and the
VLAN configuration is not changed.
Table 10-7 Default VMPS Client and Dynamic-Access Port Configuration
Feature Default Setting
VMPS domain server None
VMPS reconfirm interval 60 minutes
VMPS server retry count 3
Dynamic-access ports None configured
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