Digisol DG-GS1550, Management Manual

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Introduction
1-4
1
Store-and-Forward Switching – The switch copies each frame into its memory
before forwarding them to another port. This ensures that all frames are a standard
Ethernet size and have been verified for accuracy with the cyclic redundancy check
(CRC). This prevents bad frames from entering the network and wasting bandwidth.
To avoid dropping frames on congested ports, the switch provides 4 Mbits for frame
buffering. This buffer can queue packets awaiting transmission on congested
networks.
Spanning Tree Algorithm – The switch supports these spanning tree protocols:
Spanning Tree Protocol (STP, IEEE 802.1D) – This protocol provides loop detection
and recovery by allowing two or more redundant connections to be created between
a pair of LAN segments. When there are multiple physical paths between segments,
this protocol will choose a single path and disable all others to ensure that only one
route exists between any two stations on the network. This prevents the creation of
network loops. However, if the chosen path should fail for any reason, an alternate
path will be activated to maintain the connection.
Rapid Spanning Tree Protocol (RSTP, IEEE 802.1D-2004) – This protocol reduces
the convergence time for network topology changes to 3 to 5 seconds, compared to
30 seconds or more for the older IEEE 802.1D STP standard. It is intended as a
complete replacement for STP, but can still interoperate with switches running the
older standard by automatically reconfiguring ports to STP-compliant mode if they
detect STP protocol messages from attached devices.
Multiple Spanning Tree Protocol (MSTP, IEEE 802.1D-2004) – This protocol is a
direct extension of RSTP. It can provide an independent spanning tree for different
VLANs. It simplifies network management, provides for even faster convergence
than RSTP by limiting the size of each region, and prevents VLAN members from
being segmented from the rest of the group (as sometimes occurs with IEEE 802.1D
STP).
Virtual LANs – The switch supports up to 256 VLANs. A Virtual LAN is a collection
of network nodes that share the same collision domain regardless of their physical
location or connection point in the network. The switch supports tagged VLANs
based on the IEEE 802.1Q standard. Members of VLAN groups can be dynamically
learned via GVRP, or ports can be manually assigned to a specific set of VLANs.
This allows the switch to restrict traffic to the VLAN groups to which a user has been
assigned. By segmenting your network into VLANs, you can:
• Eliminate broadcast storms which severely degrade performance in a flat network.
• Simplify network management for node changes/moves by remotely configuring
VLAN membership for any port, rather than having to manually change the network
connection.
• Provide data security by restricting all traffic to the originating VLAN.
• Use private VLANs to restrict traffic to pass only between data ports and the uplink
ports, thereby isolating adjacent ports within the same VLAN, and allowing you to
limit the total number of VLANs that need to be configured.
• Use protocol VLANs to restrict traffic to specified interfaces based on protocol type.