Chapter 69 Switch Operation; Address Table; Learning; Forwarding & Filtering - Planet XGS3-42000R User Manual

Chapter 69 SWITCH OPERATION

69.1 Address Table

The S witch is implemented with an address table. This address table composed of many entries. Each entry
is used to store the address information of some node in net work, including MAC address, port no, etc. This
in-formation comes from the learning process of Ethernet Switch.

69.2 Learning

When one packet comes in from any port, the Switch will record the source address, port no. And the other
related information in address table. This information will be used to decide either forwarding or filtering for
future packets.
69.3 Forwarding & Filtering
When one packet comes from some port of t he Ethernet Switching, it will also check the destination address
besides the source address learning. The Ethernet Switching will look up the address-table for the destination
address. If not found, this packet will be forwarded to all the other ports except the port, which this packet
comes in. And these ports will transmit this packet to the network it connected. If found, and the destination
address is located at different port from this packet comes in, the Ethernet Switching will forward this packet to
the port where this destination address is located according t o the information from address table. But, if the
destination address is located at the same port with this packet comes in, then this packet will be filtered.
Thereby increasing the net work throughput and availability

69.4 Store-and-Forward

Store-and-Forward is one type of packet-forwarding techniques. A Store-and-Forward Ethernet Switching
stores the incoming frame in an internal buffer, do the complete error checking before transmission. Therefore,
no error packets occurrence, it is the best choice when a network needs efficiency and stability.
The Ethernet Switch scans the destination address from the packet-header, searches the routing table
pro-vided for the incoming port and forwards the packet, only if required. The fast forwarding makes the
switch attractive for connecting servers directly to the net work, thereby increasing throughput and availability.
How-ever, the s witch is most commonly used to segment existence hubs, which nearly always improves
overall performance. An Ethernet Switching can be easily configured in any Ethernet network environment to
signifi-cantly boost bandwidth using conventional cabling and adapters.
Due t o the learning function of the Ethernet switching, the source address and corres ponding port number of
each incoming and outgoing packet are stored in a routing table. This information is subsequently used to
filter packets whose destination address is on the same segment as the source address. This confines
network traffic to its respective domain and reduce the overall load on the net work.
The Switch performs "Store and forward" therefore, no error packets occur. More reliably, it reduces the
re-transmission rate. No packet loss will occur.
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