What is a router?

A router is the most common device in a network, used to implement WAN and LAN connections, provide the best path for datagrams, and forward data. A router consists of a CPU, RAM (Random Access Memory), ROM (Read Only Memory), and an operating system. Among them, the CPU is used to execute the instructions of the operating system; the RAM can run the operating system, run the configuration file and save the IP routing table, and the content stored in the RAM will be lost when the power is turned off; ROM can save the power-on self-test software, and store the router’s boot program, etc.

Routers are used to connect different networks. Therefore, routers support multiple types of physical interfaces. The interfaces are generally on independent interface modules, and a few interfaces are also on the motherboard. Interfaces are mainly divided into three categories: management interface, local area network interface and wide area network interface. Router management interfaces include console terminals and auxiliary ports. During initial installation, the router is configured locally using the console terminal; if the router is remotely located, a connection to the modem through the auxiliary port is required to configure the router. The local area network interface is used to realize the access of the local area network, and the WAN interface is used to connect the external network, and the router is connected to each different network through these physical interfaces. At present, the typical interfaces of routers include Ethernet interface (10M/100M/1000Mbps), serial port, CPOS port and E1 port.

1. Equipment introduction

Take H3C MSR3600-28 as an example, which is a multi-service router. It can be used as an egress router for small and medium-sized enterprises, as a branch access router for governments or enterprises, and as a business gateway for enterprise network VPN, NAT, and IPSec. The height of the router is one rack height (1RU). For indoor use, the MSR3600-28 adopts the cooling method of left air inlet and right air outlet. The air inlet and air outlet of the router cannot be blocked and there must be enough space. The router can be placed on the desktop. At this time, glue pads must be attached to the four corners of the bottom of the router, and the glue pads must be in firm contact with the desktop. The more common installation method is to install the router in the rack through the mounting ears, as shown in Figure 1.

What is a router?
Figure 1 – Router mounted in rack with mounting ears

MSR3600-28 has abundant interfaces, the front panel has 24 LAN Ethernet interfaces, 3 WAN Ethernet interfaces, and 1 Console/AUX port. The LAN Ethernet interface is used to connect with the local area network equipment, and the WAN Ethernet interface is used to connect with the WAN equipment. The Console/AUX port is the management port. The MSR3600-28 rear panel has 4 SIC slots. The SIC slot supports various types of SIC interface modules, such as serial interface module, voice module, Ethernet interface module and E1 interface module. When installing the SIC interface module, first remove the dummy panel, and then insert the SIC interface module. It should be noted that the SIC interface module does not support hot swapping, and the router must be powered off before installing the interface module. The MSR3600-28 supports -48~-60V DC power modules, or 100~240V AC power modules.

2. Introduction to the interface module

The powerful multi-service capability of the router comes from its rich interface modules. The following introduces several typical interface modules, including Fast Ethernet module SIC-4FSW, Gigabit Optical Ethernet interface module SIC-1GEC, E1 interface module SIC-2E1-F and serial interface module SIC-8AS.

The SIC-4FSW interface module is a 4-port 10M/100M Ethernet SIC module, as shown in Figure 2(a), which can be directly inserted into the SIC slot. This module mainly realizes the Layer 2 switching function of 4-way Ethernet, and can also realize the Layer 3 switching function. It can provide 4 10/100Base-Tx Ethernet ports on the router, which is suitable for switching/routing integrated equipment in the small enterprise network, and can directly connect the PC and network equipment in the enterprise. When the user adopts Category 5 twisted pair, the transmission distance is 100m. Any Ethernet interface on the module can work at two speeds of 100Mbit/s or 10Mbit/s, with full-duplex and half-duplex working modes.

SIC-1GEC is a 1-port Gigabit Optical Ethernet interface module, as shown in Figure 2(b). The module can be directly inserted into the SIC slot, providing an Ethernet interface with a rate of 1000Mbit/s. The interface type can be an electrical interface or an optical interface. When used as an optical interface, an SFP module needs to be configured separately. The SIC-1GEC module is a COMBO interface, and cannot support both optical and electrical interfaces. The default is the electrical interface when powered on. If the optical interface is to be used, it needs to be configured with commands.

What is a router?
Figure 2 – SIC-4FSW and SIC-1GEC interface module panel

SIC-2E1-F is a 2-port E1 interface module, as shown in Figure 3(a). The module can be directly inserted into the SIC slot. The module needs to be equipped with a special cable, which can be converted into two 75Ω E1 interfaces through the cable.

SIC-8AS is an 8-port asynchronous serial interface module, as shown in Figure 3(b). The module can be directly inserted into the SIC slot. The module needs to be equipped with a special cable, which can be converted into 8 asynchronous serial ports through the cable. The main function of the SIC-8AS interface module is to complete the sending, receiving and processing of asynchronous data streams. The maximum rate of each asynchronous serial port reaches 115.2Kbit/s; it can support terminal access services and asynchronous private lines. When the asynchronous serial port is used for dialing, it can be used as a dial-up access server for small and medium-sized ISPs.

What is a router?
Figure 3 – SIC-2E1-F and SIC-8AS interface module panel