VLAN Advanced Setup

There is detailed information about Distributed and Stand-alone VLANs, Domain Name and IP Links after the parameter explanations.

VLAN Mode
Valid input Stand-alone or Distributed. If you have inserted an ATM Module in your device, it is not possible to use distributed VLANs.
Default value Stand-alone.
VLAN Domain Name
Valid input 0 to 8 alphanumeric characters.
Default value None.
Server Priority
Valid input 1 to 65535
Default value 32768
Function Assigns a server priority to a particular device.
Comment By default the function of server is assigned to the device with the lowest MAC address. To make another device server, that device must be assigned a higher priority than the default server.
Server Expiry Timeout
Valid input 10 to 65535
Default value 50 seconds
Comment If contact is lost with the server after the time specified the device with the next highest priority becomes the server.
Main IP Link to SNMP Management VLAN
Valid input Enable, disable
Default value Enable
Function As you select a new VLAN to manage SNMP, the main IP link moves to this VLAN.
Comment If disabled, you may lose connectivity with the switch. The field is disabled if the switch is a desktop switch (no routing), or you have made changes elsewhere in the VLAN setup.

 

Distributed VLAN only

To use the VLAN feature in a set of switches, at least one of the switches must have a configured VLAN policy database. This switch forwards the global information to the other switches, ensuring the policy is identical on all the switches. This information is then sent on the links that connect the switches, these links are called switch VLAN links (SVL).

When receiving a packet on a non-SVL from a station which is not learned (for example, a packet with a source MAC address not present in the switch's filter memory), the VLAN learning process will match the packet against the configured policies. As a result of this match, the station will now participate in the VLANs and the packets from this station can be forwarded to members of the same VLAN(s) because the MAC address is placed in the switch's filter.

Auto-learning

 

If there is no match for the packet (for example, no membership of a VLAN) the station will still be regarded as unknown and will never be able to forward packets through the switch. To alter this, it is possible to auto-learn VLAN relationships (for example, IP addresses) by processing all ARP packets.

Example

If a station not belonging to any VLANs sends an ARP packet, it is discarded and the normal learning process is initiated. If the station belongs to one or more VLANs, the ARP packet is forwarded immediately (according to the normal procedure) and the packet is processed by the switch and a new VLAN membership will eventually be updated.

When the VLAN learning process is inserting a station in a VLAN, it is important that this information is distributed to the other switches, so they can update their VLAN knowledge (and filters). The information to be distributed is the MAC-VLAN mapping and must be identical on all the switches. This protocol distributes the MAC addresses and the VLAN to which they belong.

Packets with an unknown destination address

 

When a packet with an unknown destination address is observed on a non-SVL, the packet is flooded in the VLANs the source station belongs to. To avoid flooding to all the switches in the network, a protocol is developed, where each switch tells the neighboring switches which VLANs it has access to. In this way the switch has only to flood a packet to the switches which have access to the correct VLAN.

When you create a virtual LAN containing the management PC's IP address and IP learning is enabled, the switch follows the IP learning rules to learn the management PC's MAC address. So, when the PC sends an Address Resolution Protocol (ARP) request to the switch, the PC's MAC address is added to the VLAN.

Stand-alone VLAN only

If you try to create a virtual LAN with the Confirm connectivity option enabled and the management PC is removed from the virtual LAN, connectivity ends. The management PC's MAC address is removed from the VLAN and the switch cannot communicate with the management PC.

The switch restores the previous configuration that was valid before the changes. In the worst case, you may have to wait approximately 15 minutes for another ARP request to be sent; once the ARP entry has timed out, another ARP is sent from the management PC and the connectivity is restored.

A message appears if there is a chance of losing SNMP connectivity to the device.

If another management station is configuring a VLAN on this device, a message is displayed, and the Add, Delete, Routing and Policies buttons are unavailable.

Domain name

To ensure the VLAN only only on selected switches, it is given a domain name. The domain name is used as an authentication check in the inter-switch packets on the Switch VLAN Link (SVL).

The domain identifies the coverage of the VLAN configuration-both the VLAN mappings and configuration protocols. By giving the same domain name to all the switches, they will all follow the same policies.

 

More info about

VLAN FAQ


Procedures

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