LAN Switches: A Trend Worth Following…

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Aswitch is a special type of hub that forwards packets to the appropriate port based on the packet’s address, automatically learns network addresses, and gives each sender-receiver pair the full bandwidth of the network. A switch segments networks into different subnets, thus keeping the network from being overloaded with traffic.

Typically, a switch can either be unmanaged or managed. A managed switch can either be a stackable switch or a chassis switch.

Layer 5 Switches Gain Popularity

The layer 5 (L5) switch aims to use session level information in addition to layer 2-3-4 information to route traffic in the network. The L5 system consists of a switch core to which a number of custom- built intelligent port controllers are attached. In addition, it is equipped with a processor complex. The job of the port controllers is to identify the packets that require layer 5 processing and forward them to the processor. The port controllers process the rest of the packets. As the CPU processes only a very small fraction of the packets, it achieves very high speeds while delivering useful layer 5 functionality. In fact application level proxies, which are functionally equivalent to the L5 switch, have been around for years. L5 combines the functionalities of an application layer proxy and the data handling capabilities of a switch into a single system. Though it can be used anywhere in the network the L5 switch is most useful as a front-end to a server cluster. It makes it possible to partition the URL space among the server nodes thus improving the performance of the server cluster.

n Unmanaged Switches: The unmanaged standalone switches are gradually replacing hubs in most networks. These switches allow simultaneous transmission of multiple packets via an internal high-speed data channel. The learning function in the switch stores the address and corresponding port number of each incoming and outgoing packet in a routing table. This information is subsequently used to filter packets whose destination address is on the same segment as the source address.

A typical unmanaged switch comes with the following features:

Automatic detection of MDI-X and MDI crossover
Conformation to IEEE 802.3 10BASE-T and IEEE 802.3u 100 BASE-TX specifications
Store-and-forward scheme to forward packets
Frame filtering and forwarding for each port
Automatic MAC address learning and aging
Automatic local traffic filtering
Auto-negotiation on duplex mode

n Stackable Switches: The stackable switches are those where different standalone switches are combined to perform the function of a single large switch.

A typical stackable switch comes with the following features:

Fault tolerance so that if one switch fails, the other switches in the stack can continue to operate
Port redundancy so that if one port fails, a backup port can be automatically substituted
Hardware/software to let the user manage the switches using the Simple Network Management Protocol

n Chassis Switches: These are much larger with several chassis/line cards, each having several ports.

In addition, switches are also classified by the functionalities of the layers of the OSI model of networking.

n Layer 2 switches: These are manageable switches that enable an administrator to monitor the traffic passing through each port and to configure each port in the switch. Besides, a typical layer 2 switch comes with the following features:

IEEE 802.1D Spanning Tree support
GVRP (GARP VLAN Registration Protocol) support for VLAN membership management
IGMP snooping, to prevent broadcast traffic from flooding to all the ports within the switch.
Link aggregation to improve the uplink traffic performance and provide link redundancy.
IEEE 802.1Q/p support for VLAN and priority

Main Vendors

l	Cisco Systems
l	D-Link
l	Nortel Networks
l	Enterasys Networks
l	3Com

n Multiple Layer Switches: Switches support multiple layers (2, 3, and 4) protocols to protect against obsolescence and to add new services such as traffic classification, protocol filtering, and multicast to handle and prioritize different types of traffic.

A typical multilayer switch has the following features:

Supports RIP v1, v2 and OSPF routing functions.
Supports multi-netting assigning multiple IP protocol interfaces to the same physical port
Supports classless inter-domain routing (CIDR) to enable the efficient allocation of the IP address space
Serves as DHCP server or client or relay
Serves as DNS server or proxy
Access control list for enhancing security purpose
Bandwidth management for better usage

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