Lecture Series on IP network design (4): Lan design (1)

This is the last part of the IP network design series. This article will discuss some problems encountered in the design of campus LAN. The advantages of Ethernet switches over the traditional hub environment will be described first. The motivation for applying a virtual LAN has been studied together with the problems encountered in planning and configuring a virtual LAN. This article will also discuss some technologies that ensure the design of campus networks is scalable and elastic. This article will also discuss the Spanning Tree Protocol and how to optimize it in a large exchange network. Finally, the conclusions in this article will involve the design issues related to the launch of IP phones.

Benefits of Ethernet Switching

The traditional shared Ethernet is a baseband medium. This means that only one site can send data to the media at any time. Multiple signals cannot become multiplexing signals as in the broadband network media. In a shared Ethernet Hub, each site checks whether other sites are sending data by listening to a pair of lines received by children. In this way, access conflicts are solved. The Ethernet Switching application replaces the shared Ethernet, resulting in the following improved operation functions:

Dedicated conflict domains

Each port of a vswitch is in its own conflict domain. Therefore, a site connects to the LAN through the port of a vswitch, rather than through the port of a hub. In this way, the site does not need to compete for access to the line by listening for conflicts before sending data. This will increase the effective bandwidth of the LAN.

Communication filtering and forwarding

A vswitch works like a multi-port bridge and monitors live communication to know the location of the MAC address of each site. For each frame exchanged by the switch, the switch only forwards the communication to the port of the destination MAC address. The switch is said to be used to filter frames on all other ports. This will significantly reduce unnecessary communications in the LAN and improve bandwidth utilization. However, broadcast frames will flow to all ports. In this way, a vswitch is said to have created multiple conflicting domains, but all ports are still in the same broadcast domain. This is usually an ideal way of working, because broadcasting is necessary, usually an effective means of communication in the LAN. This is somewhat different from the WAN. Microsoft uses NetBios, which is heavily reliant on broadcast, for Windows. Another example is the IP Address Resolution Protocol (ARP ). According to the Address Resolution Protocol, An Address Resolution Protocol broadcast must reach each site of the IP subnet to resolve the IP address of a destination to a MAC address.

Full-duplex transmission

Traditional shared Ethernet works in half duplex mode. In other words, each site cannot send and receive data at the same time. Due to the nature of the Ethernet baseband, only one site can access the media and send data at any time. Each site on a shared Ethernet medium solves communication conflicts through listening conflicts. Full duplex transmission means that all sites can send and receive data simultaneously. In Ethernet, this is not achieved by monitoring conflicts. If the site is attached to its own dedicated switch port, it only legally disables the conflict detection function. This means that there are only two sites in the conflicted domain: the site itself and the port of this switch. Then, each site can send and receive data from each other without listening for conflicts. This method is called point-to-point Ethernet. Like many network terms, full duplex has been abused and some claims are untrue. The marketing war between switch manufacturers prompted them to claim that full-duplex jobs can double the data throughput. Full-duplex jobs can indeed significantly improve data throughput, but it cannot be said that the data throughput is doubled, because it is impossible for a site to send and receive applications simultaneously at a wire speed.

Understanding client-server communication flow

When implementing an exchange LAN design, obtaining a detailed understanding of the client-server communication stream is probably the biggest challenge. A network is being redesigned to transform a shared LAN environment into an exchange LAN to meet increasing bandwidth requirements. In this case, it is possible to collect a large amount of detailed information about the communication status. It is not easy to collect this information before a new network is launched. However, there is no strict analysis of the number of communication conditions, and a reasonable quality analysis of the communication conditions should also be achieved. Reasonable prediction of the following information is very important: who is talking to what server, how long is the call time, and how much bandwidth is consumed now, what is the bandwidth consumed in the future? What are the physical and logical locations of all clients and servers. In other words, you must have a clear understanding of the data channels between the client and the server of each application. What is the communication level between servers? Again, this is consistent with the need to understand all major communication flows of the entire network. If you do not fully understand these communication flows, the role of LAN switches is limited. To give an extreme example, assume that a server is far away and must be accessed through a 56 K Wan line. In this case, a LAN switch cannot significantly improve performance because the bottleneck is in the WAN rather than in the LAN.

High-speed Kernel

Some proprietary methods and the 802.3ad standard allow the integration of multiple connections into a logical high-speed connection. Multiple physical connections between two vswitches must be treated as one logical connection. Otherwise, the spanning tree blocks redundant connections. This function can be used to provide high-speed connections between core switches and high-speed connections to high-bandwidth servers. Even before applying 10-ge Ethernet, a maximum of eight Ethernet ports can be integrated to provide the High-Speed campus trunk line function.