What is Router? Router is a device which makes communication between two or more networks present in different geographical locations. Routers are data forwarding devices which work at Layer 3. Routers forward data based on logical addresses (IP, IPX, Appletalk). Companies that manufacture Routers: - Cisco- Juniper - Nortel- Multicom - Cyclades- Dlink - Linksys- 3Com

Cisco's Hierarchical Design Model Cisco defined the Router into 3 Layers Access Layer Router Distribution Layer Router Core Layer Router

Access Layer Router Routers which are used by small organisations. Used for end user connectivity. Router Series: 800, 1600, 1700, 2500, 2600

Distribution Layer Router Router which are used by the ISPs. Used for policy based routing and access control. Router Series: 2600, 3200, 3600, 3700.

Core Layer Router Routers which are used by the Global ISPs. Used for fastest switching across internet. Router Series: 6400, 7200, 7300, 7400, 7500, 7600, 10000, 12000

Modular Router

Cisco 2501

Attachment Unit Interface It is used for connecting LAN to the Router. It is known as Ethernet Port or LAN port. AUI has 15-pin female connector (DB-15). Transceiver is used to connect RJ-45 to DB-15.

Attachment Unit Interface An IP address is to be assigned to this interface and it should be in the same network as of the LAN.

Attachment Unit Interface A cross-cable is used to connect AUI of the Router to PC-NIC

Crimping of Twisted Pair Cable Straight Cable Cross Cable

Crimping of Twisted Pair Cable Uses:

Crimping of Twisted Pair Cable Roll Over Cable Used for connecting Router Console Port to PC COM Port or Serial Port.

Serial port Serial interface has DB60 connector (60 pins) in fixed routers. Small Serial interface has DB26 connector in modular routers. It is known as WAN Port. It is used for connecting Remote Locations using V.35 cable, which has 60-pins (male connector) at one end and 18-pins (male connector) on the other end.

Serial port

Console Port It is known as Local Administrative Port. It is used for Initial Configuration. Password Recovery.

Console Connectivity Connect one end of the rollover cable to the router's console port (RJ- 45 connector) and the other end of the cable to DB-9 converter. Attach the female DB-9 converter to a PC Serial Port. Use Terminal Emulation software like HyperTerminal, Putty, TeraTerm and so forth. Open minicom -s (when using a Linux OS)

Auxiliary Port It is known as Remote Administrative Port. Used for remote administration.

Other Ports BRI Port Basic Rate Interface used to connect ISDN. It is available on 2503 and 2520 model routers. Used for connecting LAN to the Router. It is available on 2520 model router. 10BaseT Port

2601 Model Router

Brief Overview WAN Interfaces Serial Interfaces (S0,S1) ISDN Interfaces (BRI0) LAN Interfaces - (Ethernet) AUI (Attachment Unit Interface) (E0) 10baseT Fast Ethernet - fa0 Administrative Interfaces Console port Auxiliary port

Internal Components ROM – Read Only Memory A bootstrap program is located here. It contains POST routines. Internetwork Operating System (IOS) is stored here. IOS is Command Line Interface (CLI). Flash RXboot mode (mini IOS), ROM monitor mode are also located here

Internal Components NVRAM - Non Volatile RAM The Startup Configuration of the router is stored permanently when it is saved here. It is temporary storage memory where Running Configuration is stored. RAM - Random Access Memory The size of RAM is greater than NVRAM. Motorola Processor 30 MHz, RISC (Reduced Instruction Set Computer) based processor Processor

Internal Components

Boot Sequence

Router Boot sequence: – a series of steps a Cisco router performs when booting up – to test the hardware and load the necessary software.

Boot Sequence router performs a POST (Power On Self Test) It tests the hardware to verify that all components of the device are operational and present. POST is stored in and run from ROM. E.g. POST checks for the different interfaces on the router

Boot Sequence The bootstrap program checks the Configuration Register value to find where to load the IOS. The bootstrap is a program in ROM that is used to execute programs. The default value of configuration register is 0x2102. This value indicates that the router should load CISCO IOS software image from flash memory. Flash memory is the default location

Boot Sequence Another possible location of IOS Image is a TFTP server. Trivial File Transfer Protocol. typically used by network administrator to copy configuration file, log file and firmware to/from networking devices. small, simple and easy to implement UDP, port 69

Boot Sequence If the Bootstrap program is not able to find a valid IOS image, it will act as ROM Monitor ROM monitor is capable of performing certain configuration tasks : – Download IOS image using TFTP – Recovering a lost password. – Changing configuration register values.

Boot Sequence The IOS software looks for a valid configuraion file stored in NVRAM. The file is called startup-config. If the startup configuration file is present in the NVRAM, the router will load and apply those configuration commands in the startup-config file. If a valid startup configuration file is not present in the NVRAM, IOS will display System Configuration setup.

Boot Sequence Once the startup-config configuration is loaded, IOS will present CLI interface in user mode.