in a simple or complex network, the router is the core of the connection of different equipment and different segment communication devices, in both public and private network are responsible for the data transmission of the key centers of the function.
this paper to explain the various hardware routers structure: the CPU, memory, interface, the console port and auxiliary port, and explains the router during the process of electric start.
router is a kind of connecting multiple network or segment of the network equipment, it can data between different networks or network segment information Translation "So that they can mutually Read "Understand each other's data, so as to form a larger network.The router is composed of hardware and software.Hardware mainly by the CPU, memory, interface and control port of the physical hardware and circuit;The software is mainly composed of a router IOS operating system.
today, we in the current widely used Cisco router, for example to introduce you to the router hardware and its working conditions.Let everyone at the same time of using them, for some idea of what they are made also.
as the central processor
and computer, the router also contains a central processing unit (CPU).Different series and types of routers, the CPU is not the same.Motorola 68030 commonly used Cisco router and Orion/R4600 two processors.The CPU
router is responsible for the router's configuration management and packet forwarding work, such as maintaining the router needs many kinds of form and routing algorithm, etc.Routers for packet processing speed greatly depends on the type of CPU and performance.
router memory adopted several different types of memory, each memory help router work in different ways.
1. Read only memory (ROM)
read-only memory (ROM) in the Cisco router function similar to computer the ROM, it is mainly used for system initialization, and other functions.ROM mainly include: (1)
system and electricity self-inspection code (POST), used to test the router in the hardware parts are in good condition;
(2) the system boot area code (the BootStrap), used to launch the router and into the IOS operating system;
(3) the backup of the IOS operating system, so that the original IOS operating system to be deleted or destroyed.Usually, this version of the IOS is now running IOS lower, but enough to make the router startup and work.
as the name implies, ROM is read only memory (ROM), deposit cannot modify the code.If you want to upgrade, to replace the ROM chip.
2. Flash memory (Flash)
Flash memory (Flash) can be read to write memory, the system can still save the data after restart or shutdown.In the Flash with the current use of IOS.In fact, if the Flash capacity is big enough, even can hold multiple operating systems, this is very useful when upgrading the IOS.When I do not know if the new IOS stable, but still keep the old version after the upgrade IOS, when problems can be quickly returned to the older operating system, so as to avoid long time of network failure.
3. The Nonvolatile RAM (NVRAM)
Nonvolatile RAM (Nonvolatile RAM) can be read to write memory, the system can still save the data after restart or shutdown.Because the NVRAM is only used to save the Startup configuration file (Startup - Config), so the capacity is small, usually on the router configuration only 32 KB to 128 KB NVRAM.At the same time, the NVRAM faster, the cost is high.
4. Random access memory (RAM)
RAM is readable writable memory, but the content of it is stored in the system will be cleared after restart or shutdown.And RAM in computer, RAM in the Cisco router is running operating system and the temporary storage of data during the period of memory, let the router can quickly access the information.RAM access speed is superior to the previously mentioned three kinds of memory access speed.During the running of
RAM contained in the routing table project, ARP cache, logging projects, and the queue waiting to send the packet.In addition, also including the Running configuration file (Running - config), the executing code, the IOS operating system program and some temporary data information.
router types, IOS code reading methods are also different.Such as Cisco 2500 series router only if there is a need to read in part from the Flash IOS;And the entire Cisco 4000 series router IOS all must first be loaded into RAM to run.Thus, the former is called Flash operation equipment (Run from Flash), the latter is called RAM operation equipment (Run from RAM).
routers, electric start-up process:
(1) the system hardware and electricity self-inspection.Running ROM the hardware test procedure, test components can work normally.After finishing the hardware detection, start software initialization.
(2) software initialization process.Run in the ROM BootStrap program, carries on the preliminary work boot.
(3) to find and load the IOS file system.IOS file can be stored in many place, as to which one the IOS, is through the command to set the specified.
(4) the IOS loading is completed, the system search stored in NVRAM Startup - Config files, system configuration.If NVRAM Startup - exist in the Config file, will be transferred to RAM the document and detailed execution.Otherwise, the system to enter the Setup mode, the initial configuration of router.
all routers have Interface (Interface), each Interface has its own name and number.A the full name of the interface formed by its type symbol and number, serial number starting from 0.
for fixed router interface (such as Cisco 2500 series) or modular interface of the router (e.g., Cisco 4700 series), in the full name of the interface, use only a number, and according to their physical order number in the router, such as Ethernet0 said the first Ethernet interface, Serial1 said second serial port.Support for the
Online insertion and deletion "Or physical interface configuration of a router to dynamically change, its interface is all in the name contains at least two Numbers, separated by slashes / "Segmentation.Among them, the first number represents slot number, the second number represents interface card in the port number.Such as Cisco 3600 router, representative serial3/0 1 in 3 slots on a serial port.Support for the
Universal interface processor (VIP) "Routers, its interface number form for Slot/port adapter/port ", such as Cisco 7500 series router, Ethernet4/0/1 refers to the slot number 4 first port adapter 2 Ethernet interfaces.
all routers have installed the console port, the user or administrator can use to communicate with terminals and routers, complete the router configuration.The port provides an asynchronous serial interface, the EIA/TIA - 232 used in local to the router is configured (configuration should be carried out through the console port) for the first time.
router model is different, and the console are connected by way of the concrete interface is different also, some use DB25 connector DB25F, some USES RJ45 connector.Usually, the smaller the router USES RJ45 connector, and the larger the router USES the DB25 connector.
most routers are equipped with an auxiliary port, it is similar to the console port, provides an asynchronous serial interface, the EIA/TIA - 232 commonly used to connect the Modem to the user or administrator right by remote control.