Allied Telesis AT-9724TS Port-based VLANs, Vlan Segmentation, Vlan and Trunk Groups, Switch Ports

An example is presented below:
	VLAN Name	VID	Switch Ports
	System (default)	1	5, 6, 7, 8, 21, 22, 23, 24
	Engineering	2	9, 10, 11, 12
	Marketing	3	13, 14, 15, 16
	Finance	4	17, 18, 19, 20
	Sales	5	1, 2, 3, 4

Table 6- 3.VLAN Example – Assigned Ports

Port-based VLANs

Port-based VLANs limit traffic that flows into and out of switch ports.Thus, all devices connected to a port are members of the VLAN(s) the port belongs to, whether there is a single computer directly connected to a switch, or an entire department.

On port-based VLANs, NICs do not need to be able to identify 802.1Q tags in packet headers. NICs send and receive normal Ethernet packets. If the packet's destination lies on the same segment, communications take place using normal Ethernet protocols. Even though this is always the case, when the destination for a packet lies on another switch port,VLAN considerations come into play to decide if the packet gets dropped by the Switch or delivered.

VLAN Segmentation

Take for example a packet that is transmitted by a machine on Port 1 that is a member of VLAN 2. If the destination lies on another port (found through a normal forwarding table lookup), the Switch then looks to see if the other port (Port 10) is a member of VLAN 2 (and can therefore receive VLAN 2 packets). If Port 10 is not a member of VLAN 2, then the packet will be dropped by the Switch and will not reach its destination. If Port 10 is a member of VLAN 2, the packet will go through.This selective forwarding feature based on VLAN criteria is how VLANs segment networks.The key point being that Port 1 will only transmit on VLAN 2.

Network resources such as printers and servers however, can be shared across VLANs.This is achieved by setting up overlapping VLANs.That is ports can belong to more than one VLAN group. For example, setting VLAN 1 members to ports 1, 2, 3, and 4 and VLAN 2 members to ports 1, 5, 6, and 7. Port 1 belongs to two VLAN groups. Ports 8, 9, and 10 are not configured to any VLAN group.This means ports 8, 9, and 10 are in the same VLAN group.

VLAN and Trunk Groups

The members of a trunk group have the same VLAN setting.Any VLAN setting on the members of a trunk group will apply to the other member ports.

Note: In order to use VLAN segmentation in conjunction with port trunk groups, you can first set the port trunk group(s), and then you may configure VLAN settings. If you wish to change the port trunk grouping with VLANs already in place, you will not need to reconfigure the VLAN settings after changing the port trunk group settings.VLAN settings will automatically change in conjunction with the change of the port trunk group settings.

Protocol VLANs

The AT-9724TS incorporates the idea of protocol-based VLANs.This standard, defined by the IEEE 802.1v standard maps packets to protocol-defined VLANs by examining the type octet within the packet header to discover the type of protocol associated with it.After assessing the protocol, the Switch will forward the packets to all ports within the protocol-assigned VLAN.This feature will benefit the administrator by better balancing load sharing and enhancing traffic classification.The Switch supports fifteen (15) pre-defined protocols for configuration.The user may also choose a protocol that is not one of the fifteen defined protocols by properly configuring the userDefined protocol VLAN.The supported protocols for the protocol VLAN function on this switch include IP, IPX, DEC, DEC LAT, SNAP, NetBIOS,AppleTalk, XNS, SNA, IPv6, RARP and VINES.

The following is a list of type headers for each protocol listed for VLAN configuration.

Allied Telesyn AT-9724TS High-Density Layer 3 Stackable Gigabit Ethernet Switch 58