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1.5.6.3 Protocol-based VLAN
In order for an end station to send packets to different VLANs, it itself
has to be either capable of tagging packets it sends with VLAN tags or
attached to a VLAN-aware bridge that is capable of classifying and tag-
ging the packet with different VLAN ID based on not only default PVID
but also other information about the packet, such as the protocol. The
switch can support 802.1v compliant protocol-based VLAN classifica-
tion by means of both built-in knowledge of layer 2 packet formats used
by selected popular protocols, such as Novell IPX and AppleTalk`s
EtherTalk, and others. Required configuration:
•
Protocol setting for each VLAN group defined in 802.1Q VLAN mode
•
If more than two VLAN groups are configured with same protocol
value, make sure the member ports of those groups are not overlaping.
Any incoming untagged packet is checked and classified according the
Protocol vs. VLAN mapping settings. If an associated VLAN group is
found, the packet is calssified and is inserted with VID tag of the group
VLAN ID instead of input port PVID.
1.5.7 Spanning Tree Protocol
Spanning-Tree Protocol (STP) is a link management protocol that pro-
vides path redundancy while preventing undesirable loops in the net-
work. For an Ethernet network to function properly, only one active path
must exist between two stations. Multiple active paths between stations
cause loops in the network. If a loop exists in the network, you might
receive duplicate messages. When loops occur, some switches see sta-
tions on both sides of the switch. This condition confuses the forward-
ing algorithm and allows duplicate frames to be forwarded.
To provide path redundancy, Spanning-Tree Protocol defines a tree that
spans all switches in an extended network. Spanning-Tree Protocol forces
certain redundant data paths into a standby (blocked) state. If one net-
work segment in the Spanning-Tree Protocol becomes unreachable, or if
Spanning-Tree Protocol costs change, the spanning-tree algorithm
