Notable issues in switch applications

1. Bottleneck problems in switch networks

The processing speed of the switch itself can reach very high, and the users often believe in the Gbps-class high-speed backplanes advertised by the manufacturers. In fact, this is a misunderstanding. The network used by workstations or servers connected to the Internet is a large network. It follows CSMA/CD media access rules. In the current client/server model network, multiple workstations access the server at the same time, so it is very easy to form a server bottleneck. Some manufacturers have taken this into consideration and designed one or more high-speed ports in the switch (such as 3COM's Linkswitch1000 can be configured with one or two 100Mbps ports) to facilitate users to connect to servers or high-speed backbone networks. Users can also eliminate bottlenecks by designing multiple servers (for business division) or adding multiple network cards. The switch also supports a spanning tree algorithm to facilitate user-tolerant redundant connections.

2. Broadcast frames in the network

Currently widely used network operating systems are Netware, Windows NT, etc., and the LanServer server provides services to clients by sending network broadcast frames. The existence of broadcast packets in such local area networks will greatly reduce the efficiency of the switch. At this time, the virtual network function of the switch (not every switch supports virtual networks) can be used to limit broadcast packets to a certain extent.

Each port of the switch supports a certain number of MAC addresses. In this way, the switch can “remember” the status of a group of connected sites on the port. The number of MAC addresses supported by vendors for different locations of the switch ports is not the same, and the user must use it. Note the number of connection endpoints for switch ports. If the number of MAC addresses given by the manufacturer is exceeded, when the switch receives a network frame, only the MAC address of its destination station does not exist in the MAC address table of the switch port. Then the frame is broadcasted to each port of the switch. .

3. The division of virtual networks

The virtual network is an important function of the switch. Generally, there are three types of virtual network implementations:

(1) Static port allocation

The division of a static virtual network is usually the use of network management software by the network administrator or the port of the switch is set directly to make it directly subordinate to a virtual network. These ports always maintain these slaves unless the network administrator resets them. Although this method is more troublesome, it is safer, easier to configure and maintain.

(2) Dynamic virtual network

Ports that support dynamic virtual networks can use intelligent management software to automatically determine their subordinates. The port determines the subordination of the virtual network by means of the MAC address, logical address or protocol type of the network packet. When a network node is just connected to the network, the switch port has not been allocated, so the switch dynamically assigns the port to a virtual network by reading the MAC address of the network node. In this way, once the network administrator is configured, the user's computer can flexibly change the switch port without changing the user's virtual network's dependencies, and if an undefined MAC address appears in the network, it can alert the network administrator.

(3) Multi-virtual network port configuration

This configuration allows one user or one port to access multiple virtual networks at the same time. In this way, a network server can be configured as multiple service departments (each service is set as a virtual network) can be accessed at the same time, or multiple virtual network resources can be accessed at the same time, and the connection between multiple virtual networks can only be Need a routing port to complete. However, this will bring security risks. The industry specifications for virtual networks are being developed, and the products of various companies are still not interoperable. Cisco has developed the Inter-SwitchLink (ISL) virtual network protocol, which supports virtual networks across backbone networks (ATM, FDDI, FastEthernet). However, the agreement was accused of lack of security considerations. Traditional computer networks use a large number of shared hubs, and flexible access to computer ports can also achieve good results.

4. Application of high-speed LAN technology

Although Fast Ethernet technology maintains good compatibility with traditional networks in some respects, 100BASE-TX, 100BASAE-T4, and 100BASE-FX all have relatively large restrictions on transmission distance and cascade connection. These limitations can be overcome with a 100Mbps switch. At the same time, only switch ports can support duplex high-speed transmission.

At present, CDDI/FDDI switching technology has also emerged. In addition, the CDDI/FDDI port prices have also shown a downward trend. At the same time, they have a relatively large advantage in transmission distance and security. Therefore, it is a relatively good backbone network backbone. select.