Contemporary Control Systems Compact Managed Switches Software Manual for Console Access - Manual (Page 18)

TD020850-0MG
18
4.3.5.2 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.
4.3.5.3 Two Types of VLANs
The managed switch supports two types of VLANs, Port VLAN and 802.1Q VLAN. A
Port VLAN (Section 4.2.1.5.7) 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.
4.3.5.4 Core Switches and Edge Switches
A core switch is connected only to devices that are VLAN aware — thus, all frames
received by a core switch should already contain 802.1Q VLAN tags.
An
edge switch adds VLAN tags to frames sent by non-VLAN aware devices and it
removes VLAN tags from frames destined for non-VLAN aware devices.
To function in VLAN mode, the switch requires VLAN tags. When it performs as a
Port VLAN switch (connected only to non-VLAN aware devices that do not use
VLAN tags), a default tag will be applied to the untagged frames entering the switch.
When these frames leave the switch, the tags should be removed. Thus, the switch
can act as either a core switch or an edge switch — on a port-by-port basis. This
functionality allows the switch to isolate non-VLAN aware devices by tags and give
added security.