Contemporary-control-systems Compact Managed Switches Software Manual for Web B Uživatelský manuál stáhnout pdf (Strana 22)

TD020851-0MG

4.4.4.2 VLAN Tags and VLAN Identifiers (VIDs)

Each VLAN frame contains an 802.1Q VLAN tag having a VID (VLAN Identifier)

indicating to which VLAN this message belongs. The switch can be configured to allow

frames with specific VIDs to be received on specific ports within a VLAN.

VID values can range from 1 to 4094 — but only within one contiguous block of 512

values. The allowable VID blocks (ranges) are:

1–511

512–1023

1024–1535

1536–2047

2048–2559

2560–3071

3072–3583

3584–4094

Packets having VID values outside of the one defined block will be dropped.

4.4.4.3 Two Types of VLANs

The managed switch supports two types of VLANs, Port VLAN and 802.1Q VLAN. A

Port VLAN is normally used to interconnect VLAN-unaware devices (such as desktop

computers) which do not use VLAN tags. But 802.1Q VLANs require 802.1Q tags in

the frames passing through the switch.

4.4.4.4 VLANS and Trunking

A problem can occur if all of the ports in a trunk do not share the same VLAN. If two

trunk ports were in different VLANs and one port suffered a link failure, frames would

then pass through the other port. As a result, the frames would be discarded. If more

than two ports support a trunk, the problem is not quite the same because when a path

fails, the alternate path is not user selectable — thus, the alternate port might or might

not be in the same VLAN unless all of the ports in the trunk were in the same VLAN.

Therefore, the rule when using trunking and VLANs is for all ports in the trunk to be in

the same VLAN and have the same default VID number — and every port in potential

use should have a VLAN defined for it.

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