Specifications

Chapter 3: Layer 2 Features
Extreme Networks EAS 100-24t Switch Software Manual
48
Priority tags are given values from 0 to 7 with 0 being assigned to the lowest priority data and 7
assigned to the highest. The highest priority tag 7 is generally only used for data associated with video
or audio applications, which are sensitive to even slight delays, or for data from specified end users
whose data transmissions warrant special consideration.
The Switch allows you to further tailor how priority tagged data packets are handled on your network.
Using queues to manage priority tagged data allows you to specify its relative priority to suit the needs
of your network. There may be circumstances where it would be advantageous to group two or more
differently tagged packets into the same queue. Generally, however, it is recommended that the highest
priority queue, Queue 7, be reserved for data packets with a priority value of 7. Packets that have not
been given any priority value are placed in Queue 0 and thus given the lowest priority for delivery.
Strict mode and weighted round robin system are employed on the Switch to determine the rate at
which the queues are emptied of packets. The ratio used for clearing the queues is 4:1. This means that
the highest priority queue, Queue 7, will clear 4 packets for every 1 packet cleared from Queue 0.
Remember, the priority queue settings on the Switch are for all ports, and all devices connected to the
Switch will be affected. This priority queuing system will be especially beneficial if your network
employs switches with the capability of assigning priority tags.
VLAN Description
A Virtual Local Area Network (VLAN) is a network topology configured according to a logical scheme
rather than the physical layout. VLANs can be used to combine any collection of LAN segments into an
autonomous user group that appears as a single LAN. VLANs also logically segment the network into
different broadcast domains so that packets are forwarded only between ports within the VLAN.
Typically, a VLAN corresponds to a particular subnet, although not necessarily.
VLANs can enhance performance by conserving bandwidth, and improve security by limiting traffic to
specific domains.
A VLAN is a collection of end nodes grouped by logic instead of physical location. End nodes that
frequently communicate with each other are assigned to the same VLAN, regardless of where they are
physically on the network. Logically, a VLAN can be equated to a broadcast domain, because broadcast
packets are forwarded to only members of the VLAN on which the broadcast was initiated.
Notes About VLANs
No matter what basis is used to uniquely identify end nodes and assign these nodes VLAN
membership, packets cannot cross VLANs without a network device performing a routing function
between the VLANs.
The Switch supports IEEE 802.1Q VLANs and Port-Based VLANs. The port untagging function can be
used to remove the 802.1Q tag from packet headers to maintain compatibility with devices that are tag-
unaware.
The Switch's default is to assign all ports to a single 802.1Q VLAN named "default."
The "default" VLAN has a VID = 1.
The member ports of Port-based VLANs may overlap, if desired.
IEEE 802.1Q VLANs
Some relevant terms:
● Ta gg in g - The act of putting 802.1Q VLAN information into the header of a packet.