DES-7000/DES-7100 Layer 2 Switch User
’
s Guide
Switch Management
35
Filtering done by the Spanning Tree Protocol, which can filter packets based on topology, making sure
that signal loops don't occur.
Filtering done for VLAN integrity. Packets from a member of a VLAN (VLAN 2, for example) destined
for a device on another VLAN (VLAN 3) will be filtered.
Some filtering requires the manual entry of information into a filtering table:
MAC address filtering - the manual entry of specific MAC addresses to be filtered from the network.
Packets sent from one manually entered MAC address can be filtered from the network. The entry
may be specified as a source, a destination, or both.
A listing of CLI commands for filter MAC addresses and related settings can be found in the CLI
Reference Manual in the chapter titled, Layer 2 FDB Commands. Use the menus contained in the
Forwarding and Filtering folder of the web manager to make entries into the Unicast and Multicast
forwarding tables (see page 65).
Spanning Tree Protocol
The IEEE 802.1D Spanning Tree Protocol (STP) allows for the blocking of links between switches that
form loops within the network. When multiple links between switches are detected, a primary link is
established. Duplicated links are blocked from use and become standby links. The protocol allows the
duplicate links to be used in case of a failure of the primary link. Once the Spanning Tree Protocol is
configured and enabled, primary links are established and duplicated links are blocked automatically.
The reactivation of the blocked links (at the time of a primary link failure) is also accomplished
automatically - without operator intervention.
This automatic network reconfiguration provides maximum uptime to network users. However, the
concepts of the Spanning Tree Algorithm and protocol are a complicated and complex subject and
must be fully researched and understood. It is possible to cause serious degradation of the
performance of the network if the Spanning Tree is incorrectly configured. Please carefully read
understand this section before making any changes from the default values.
The Switch allows two levels of spanning trees to be configured. The first level constructs a spanning
tree among all links between network switches. This first level is referred to as the Switch or Global
level. The second level is based on port groups. Groups of ports are configured as being members of
a spanning tree and the algorithm and protocol are applied to the group of ports. This is referred to as
the Port or VLAN level.
Spanning Tree on the Switch performs the following functions:
•
Creates a single spanning tree from any combination of switching or bridging elements.
•
Creates multiple spanning trees - from any combination of ports contained within a single
switch, in user-specified groups (usually VLANs).
•
Automatically reconfigures the spanning tree to compensate for the failure, addition, or
removal of any element in the tree.
•
Reconfigures the spanning tree without operator intervention.
Spanning is disabled system-wide by default and must be enabled in order to function switch-wide
and on a per port basis. Use the CLI command
enable stp
or use the web manager menu STP
Switch Settings (see page 63) to enable STP. To disable any individual port, use the STP Port
Settings menu (see page 64).
STP Operation Levels
STP operates on two levels: the switch level and the port or VLAN level. The switch level forms a
spanning tree consisting of links between one or more switches. The port level constructs a spanning
tree consisting of groups of one or more ports. The STP operates in much the same way for both
levels.
On the switch level, STP calculates the bridge identifier for each switch and then sets the root bridge
and the designated bridges.
On the port level, STP sets the root port and designated ports.
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