I. How to identify the performance of a switch
1. Functionality is the most direct indicator.
Application-level QoS guarantees are essential for providing greater flexibility to users in practical applications. Switch QoS policies must support multi-level packet prioritization settings, allowing for individual prioritization based on MAC address, VLAN, IP address, and port. Simultaneously, switches must possess robust congestion control and traffic limiting capabilities, supporting Diffserv differentiated services to intelligently distinguish different application flows based on source/destination MAC/IP addresses, meeting the demands of real-time multimedia applications. Currently, some switches on the market claim to offer QoS guarantees, but in reality, they only support single-level priority settings, causing significant inconvenience for users.
2. VLAN support
VLAN, or Virtual Local Area Network, enhances network management and security by dividing a local area network (LAN) into virtual VLAN segments. It controls unnecessary data broadcasting, and allows workgroups within the network to overcome geographical limitations within a shared network by dividing subnets based on management functions. Different switch manufacturers support VLANs to varying degrees, and the number of VLANs they can support also differs.
3. Network management functions
The network management function allows you to manage and configure switches using management software, such as via a web browser, Telnet, SNMP, and RMON. Typically, switch manufacturers provide management software or third-party management software for remote switch management. General switches support SNMP/MIBI/MIBII statistical management functions and support policies for configuration management, quality of service management, and alarm management. More complex gigabit switches may add built-in RMON groups (mini-RMON) to support active RMON monitoring.
4. Link Aggregation
Link aggregation allows for excellent scalability of link bandwidth between switches and between switches and servers. For example, two, three, or four gigabit links can be bundled together, multiplying the link bandwidth. In a network, redundant links are configured, and the Spanning Tree Protocol (STP) is used to block backup links, logically preventing loops. In case of a failure, the backup link is activated.
II. Why use a Layer 3 switch?
1. A network backbone cannot function without Layer 3 switching.
It's no exaggeration to describe the role of Layer 3 switches in many network devices as that of a "pillar of strength." In campus networks and metropolitan area networks, Layer 3 switches are used at the backbone, metropolitan area network backbone, and aggregation layers. In particular, the core backbone network absolutely requires Layer 3 switches; otherwise, with thousands of computers on a single subnet, there would be no security whatsoever, and broadcast storms would be impossible to isolate due to the inability to segment broadcast domains.
While traditional routers can isolate broadcasts, their performance is not guaranteed. Layer 3 switches, on the other hand, offer very high performance, combining the functionality of Layer 3 routing with the network speed of Layer 2 switching. Layer 2 switching is based on MAC addressing, while Layer 3 switching forwards traffic flows based on Layer 3 addresses. Except for the necessary routing decisions, most data forwarding is handled by Layer 2 switching, significantly improving packet forwarding efficiency.
Layer 3 switches implement IP routing functionality through hardware switching mechanisms, and their optimized routing software improves routing efficiency, solving the speed problem of traditional router software routing. Therefore, it can be said that Layer 3 switches have "the functions of a router and the performance of a switch".
2. Layer 3 switching is essential for connecting subnets.
If the number of computers on the same network exceeds a certain threshold (usually around 200, depending on the communication protocol), network transmission efficiency may suffer due to excessive broadcasting. To avoid broadcast storms caused by broadcasting on large switches, the network can be further divided into multiple virtual networks (VLANs). However, this introduces a problem: communication between VLANs must be handled by routers. Traditional routers, however, are ill-suited for handling inter-VLAN communication tasks because their routing capabilities are too limited compared to the network traffic of a local area network (LAN).
Furthermore, gigabit routers are very expensive. Using gigabit or 100Mbps ports on a Layer 3 switch to connect different subnets or VLANs economically solves the problem of subnets needing to rely on routers for communication after subnetting, while maintaining performance. Therefore, Layer 3 switches are ideal devices for connecting subnets.
