ROUTER BRIEF1.1 # INTRODUCTION AND EXPLANATION OF NETWORK ROUTER
Router is a network device that connects two or more network segments. It is used to transfer information from the source to the destination. Routers send the information in terms of data packets and when these data packets are forwarded from one router to another router then the router reads the network address in the packets and identifies the destination network. In case Gateway in networking, A network gateway is a device or node that connects disparate networks by translating communications from one protocol to another. To configure and troubleshoot a cisco internetwork, you need to know the major components of Cisco routers and understand what each one does. Below describes the major Cisco router components:
A router is a Layer3 device that connects two or more packet-switched networks or subnetworks.
a) It serves two primary functions : Managing traffic between the networks by forwarding data packets to their intended IP addresses and allowing multiple devices to use the same Internet connection.
b) Its main purpose : Receives and Sends a data on computer networks.
c) It's main features : A router works on the 3rd layer (Network Layer) of the OSI model, and it is able to communicate with its adjacent devices with the help of IP addresses and subnet. A router provides high-speed internet connectivity with the different types of ports like gigabit, fast-Ethernet, and STM link port. A router is a gateway that passes data between one or more local area networks (LANs). And there are five main types of routers in the market according to the application category.
I) Wired router : A wired router connects directly to computers through wired connections. They usually have a port that connects to the modem to communicate with the internet.
II) Wireless routers : It also called a Wi-Fi router, combines the networking functions of a wireless access point and a router. A router connects local networks to other local networks or to the Internet.
III) Core routers : It's a router designed to operate in the Internet backbone, or core. To fulfill this role, a router must be able to support multiple telecommunications interfaces of the highest speed in use in the core Internet and must be able to forward IP packets at full speed on all of them.
IV) Edge routers : An edge router is a specialized router located at a network boundary that enables an internal network to connect to external networks.
V) VPN routers : A virtual private network (VPN) router is like a normal router you would use in your home except it has a VPN installed inside it. Basic information for the above is provided for you when choosing a right one among the various routers.
1.2 # CISCO ROUTER BOOTING PROCESS EXPLAINED WITH EXAAMPLE
The internal components of Cisco router : The CPU in the router executes the commands and processes the commands in the operating system. The flow of data on the interface is controlled by the CPU. ROM: Read Only Memory in the router mainly works when the router boots up or is powered up. Internal components of a router are RAM,ROM, NVRAM, Flash Memory, CPU, RXboot Image, Interface, Configuration register.
When a router boots up, it performs a series of steps called the boot-up sequence. When you first bring-up the router then it will run on five steps and to reach the setup mode. Boot-up processing is diving into five parts: -
1) Power on self-test (POST) first to check the post on service test such as RAM, NVRAM and hardware after the power on is known as “POST”.
2) Load and run bootstrap code is load after the POST check and find the IOS software. It is the mini-program is known as “Bootstrap code”.
3) Find and load the cisco IOS configuration register file is finding the IOS from Flash memory, TFTP server and ROM. The default value of configuration register file is 2102 and one more file is also finding the IOS in flash memory with command. Switch #boot system is known as startup.config, if doesn’t find the IOS then it load the mini IOS from ROM.
4) Find and load the configuration first load the IOS in RAM and save the startup-config file and load in NVRAM after the first installation.
5) Run the configuration cisco IOS if can’t find the loaded IOS image, so system automatically goes to the setup mode.
1.3 # UNDERSTAND THE CONFIGURATION OF REGISTER BITS USAGE ON ALL ROUTER
All Cisco and all other router have a 16-bit software register that’s written into NVRAM. By default, the configuration register is set to load the Cisco IOS from flash memory and to look for and load the startup-config file from NVRAM. How to use these settings to provide password recovery on routers. The 16-bits (2 bytes) of the configuration register are read from 15 to 0, from left to right. The default configuration setting on Cisco routers is 0x2102. This means that bits 13, 8 and 1 are mentioned below : -
# The boot field (Configuration register bits 00 – 03)
| Boot field | Meaning | Use |
|---|---|---|
| 00 | ROM monitor mode | To boot the ROM monitor mode, set the configuration register to 2100. You must manually boot the router with the b cmd. The Router will show the roman> prompt. |
| 01 | Boot image from ROM | To boot an IOS image stored in ROM, set the configuration register to 2101. The router will show the Router(boot)> prompt. |
| 02 - F | Specifies a default boot file name | Any value from 2102 through 210F tells the router to use the boot commands specified in NVRAM. |
# Software configuration meanings
| Bit | Hex | Description |
|---|---|---|
| 0 – 3 | 0x0000-0x000F | Boot field |
| 6 | 0x0040 | Ignore NVRAM contents |
| 7 | 0x0080 | OEM bit enabled |
| 8 | 0x101 | Break disabled |
| 10 | 0x0400 | IP broadcast with all zeros |
| 5, 11 - 12 | 0x0800-0x1000 | Console line speed |
| 13 | 0x2000 | Boot default ROM software if network boot fails |
| 14 | 0x4000 | IP broadcasts do not have net numbers |
| 15 | 0x8000 | Enable diagnostic messages and ignore NVRAM contents |
1.4 # HOW TO RECOVER THE PASSWORD OF ROUTER, IF YOU FORGET
The default configuration register value is 0x2102, meaning that bit 6 is off. With the default setting, the router will look for and load a router configuration stored in NVRAM (startup-config). To recover a password, you need to turn on bit 6. Doing this will tell the router to ignore the NVRAM contents. The configuration register value to turn on bit 6 is 0x2142.
Here are the main steps to password recovery : -1. Boot the router and interrupt the boot sequence by performing a break, which will take the router into ROM monitor mode (Press Ctrl + Break during router bootup).
2. Change the configuration register to turn on bit 6 (with the value 0x2142).
3. Reload the router and Enter privileged mode
4. Copy the startup-config file to running-config.
5. Change the password.
6. Reset the configuration register to the default value.
7. Save the router configuration.
8. Reload the router (optional).
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Practical: Changing the configuration register
Roman 1 > prompt:
Roman 1 > confreg 0x2142
You must reset or power cycle for new config to take effect
Roman 1 > reset
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Note: In past, There are two fast-ethernet interface, four serial interfaces, plus a VPN module. The amount of RAM, NVRAM and Flash are also displayed. The above router output shows as that there is 256 Mb – RAM, 239k of NVRAM and 64 Mb of Flash memories.
1) Alphabetic key: Press N, then the configuration will be going to temporary memory.
2) Alphabetic key: Press Y, then the configuration will be going to permanent memory.
3) Each set of 4 bits (called a nibble) is read in binary with a value of 8, 4, 2, 1
There are three modes in cisco router as well as routers and have mentioned below : -
| R> User mode |
R#config t Privileged mode |
R(config)# Global mode |
|---|
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