Definition

A Router is a layer 3 network device that transmits data between different network segments and can use a packet header to determine the best path for the packet to travel. Routers can connect network sections that use different protocols. They also allow all users in a network to share a single connection to the Internet or a wide area network (WAN).

Internal Router Components

• Read-Only Memory (ROM)
  ROM stores the router’s bootstrap startup program, operating system software, and any power-on diagnostic tests programs.
• Flash Memory
  Flash Memory is reprogrammable, erasable ROM that stores the system image(s) of the operating system. Memory content is retained when the router is switched off or restarted.
• Random Access Memory (RAM)
  RAM stores operational information like routing tables while providing caching and packet buffering capabilities. Its contents are lost whenever the router is switched off or restarted.
• Nonvolatile RAM (NVRAM)
  NVRAM is used to store the router’s startup configuration file. The contents of the file are maintained whenever the router is switched on, off or restarted.
• Network Interfaces
  The router’s network interfaces are located on the motherboard or on separate interface modules. Ethernet or Token Ring interfaces can be configured to authorize connection to a LAN, while synchronous serial interfaces are configured to permit connection to WANs.

External Router Components

A router can be configured over any of its network interfaces. Trivial File Transfer Protocol (TFTP) servers can be used to provide configuration information to a router.
TFTP is a simplified version of FTP.

Router’s Startup Procedure

Every time a router is switched on; it goes through self-test diagnosis to verify the basic operation of the CPU, network interfaces, and memory.

The system bootstrap software then searches for a valid router operating system software (Cisco® IOS image). The Cisco® IOS image can be found in ROM, Flash memory, or a TSFT server on the network.

Cisco® CLI Command Modes

The Cisco® IOS software provides access to a variety of different command modes, each of which provides a different group of related commands. The Cisco® Command Line Interface (CLI) is called EXEC, and can be used in either User mode or Privileged mode. The commands available in Privileged mode are also available in User mode.

User EXEC commands allow you to:

• Connect to remote devices
• Make temporary changes to terminal settings
• Perform basic tests
• List system information

To access privileged mode, a password is required. Privileged EXEC commands can be used to:

• Set operating parameters
• Perform a detailed examination of the router’s status
• Test and debug router operation
• Access global and other included configuration modes

You can also enter global configuration mode from Privileged mode, which will give you access to configuration commands that affect the entire system.

At PC Wholesale, we guarantee compatibility for all third party Cisco memory modules, many of which are built to exceed Cisco’s specifications.  Also, all third-party memory sold by PC Wholesale has a lifetime warranty – Cisco OEM/Original memory is only under warranty for 90 days.  In addition, the cost of third party memory can be considerably less than Cisco Original/OEM memory.

Handling all users of a large private network requires that millions of traffic packets be sent at the same time. This job is handled by a router. Some of the largest routers are made by Cisco Systems, Inc., including the Gigabit Switch Router 12000 series of routers, for example, is the sort of equipment that is used on the backbone of the Internet. These routers use the same sort of design as some of the most powerful supercomputers in the world, a design that ties many different processors together with a series of extremely fast switches. The 12000 series uses 200-MHz MIPS R5000 processors, the same type of processor used in the workstations that generate much of the computer animation and special effects used in movies.

A router’s configuration table determines which of the many possibilities for an outbound connection a specific packet should take. The answer lies back in the configuration table. The router will scan the destination address and match that IP address against rules in the configuration table. The rules will say that packets in a particular group of addresses (a group that may be large or small, depending on precisely where the router is) should go in a specific direction. Next the router will check the performance of the primary connection in that direction against another set of rules. If the performance of the connection is good enough, the packet is sent, and the next packet handled. If the connection is not performing up to expected parameters, then an alternate is chosen and checked. Finally, a connection will be found with the best performance at a given moment, and the packet will be sent on its way. All of this happens in a tiny fraction of a second, and this activity goes on millions of times a second, around the world, 24 hours every day.

Knowing how and where to send a packet is the most important job of a router. Some routers do this and nothing more. Other are able to perform additional functions. Rules about where messages from inside a company may be sent and from which companies’ messages are accepted can be applied to some routers. Others may have rules that help minimize the damage from “denial of service” attacks. The one constant is that modern networks require a router to exist.

PC Wholesale carries a complete line of both Cisco Original/OEM and third party memory modules and Flash cards for every Cisco router, firewall, and switch.  Check out the Cisco Memory section to find your model and check out the available memory options.

Learning from other people’s mistakes has always been a good way, if not the best, to avoid similar problems yourself. On Global Knowledge’s training website, contributor David Davis put together a list of ”do’s and don’ts” when it comes to your Cisco Router.

The following is a summary of what he covers. You can visit the Global Knowledge site to read more detailed information about each item on the list.

#1: Not having a backup of your Cisco router configuration
- Always back up your Cisco router configuration. An easy way is to use the built in Router# copy running-configuration tftp command.

#2: Not having a backup of your Cisco router IOS software
- Always back up your software. Simply TFTP it to your server using a command like Router# copy flash tftp.

#3: Not having spare router hardware
- Have spare hardware on site should you need it.

#4: Never documenting changes
- Set up a change documentation policy so you’ll always have a history of documentation changes.

#5: Not logging your router events
- Be sure to have buffered logs on the router for temporary storage as well as a central syslog repository of Cisco router logs.

#6: Not upgrading your Cisco IOS
- Ensure your Cisco IOS is always up to date.

#7: Not knowing where to search for Cisco documentation and troubleshooting tips
- Know where to go to search the Cisco Bug database, Command Line lookups, error message decoder, your RMA orders, TAC Service requests, and Cisco netpro discussions.

#8: Forgetting your password and not knowing how to reset it
- You should know how to reset a lost Cisco password

#9: Not securing your router
- Make sure your router is secure

#10: Not spending the time to create documentation
- Prevent mistakes and downtime by documenting anything and everything.

At PC Wholesale, we guarantee compatibility for all third party Cisco memory modules, many of which are built to exceed Cisco’s specifications. Also, all third-party memory sold by PC Wholesale has a lifetime warranty – Cisco OEM/Original memory is only under warranty for 90 days. In addition, the cost of third party memory can be considerably less than Cisco Original/OEM memory.

The following addresses some common questions and procedures regarding Cisco 1700, 2600 or 3600 series routers.

How Much Memory is Installed in My Cisco 1700, 2600, or 3600 router?

 Do the following to find out the amount of memory in your router:

1. Log in to your Cisco 1700, 2600, or 3600 router.
2. Enter the show version command and press Enter. Here are examples of what you should see:

1720>show version
cisco 1720 (MPC860) processor (revision 0×601) with
36864K/12288K bytes of memory.
16384K bytes of processor board System flash (Read/Write)

2600>show version
cisco 2620 (MPC860) processor (revision 0×200) with
59392K/6144K bytes of memory.
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)

3640>show version

cisco 3640 (R4700) processor (revision 0×00) with
46080K/19456K bytes of memory.
DRAM configuration is 64 bits wide with parity disabled.
125K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)

How do I install or upgrade the memory on my Cisco 1700, 2600, or 3600 router?

Refer to the following official Cisco documents for information on upgrading memory on a Cisco 1700, 2600 or 3600 router:

• Installing and Upgrading Memory in Cisco 1700 Series Routers
• Cisco 2600 Series Memory Upgrade Configuration Note
• Installing Memory in the Cisco 3600 Router

How do I recover a password on my Cisco 1700, 2600, or 3600 router?

For information on how to recover a router password, refer to Password Recovery Procedure for the Cisco 1700 Series Routers. You can use this procedure for the Cisco 2600 and 3600 series routers as well.

How can I identify the release of Cisco IOS Software I run?

Perform the following to determine the Cisco IOS software release you are running:

1. Log in to your Cisco 1700, 2600, or 3600 router.
2. Issue the show version command and press Enter. The following shows an example of what you should see when the show version command is used on a Cisco 1700 series router.

router>show version
Cisco Internetwork Operating System Software
IOS ™ C1700 Software (C1700-O3SY756I-M), Version 12.1(5)YB4, EARLY
DEPLOYMENT RELEASE SOFTWARE (fc1)

Where can I find more information about Cisco 1700/2600/3600 routers, and ADSL WICs?

The following official Cisco documents contain information concerning installation, configuration, and troubleshooting of he Cisco 1700, 2600, and 3600 platforms and ADSL WICs. When available, data sheets are also listed.

• Cisco 1700 Series Routers
• Cisco 2600 Series Routers
• Cisco 3600 Series Routers
• Release Notes for the Cisco 1700 Series Routers for Cisco IOS Release 12.1(3)XP
• Update to Cisco WAN Interface Cards Hardware Installation Guide
• WAN Interface Cards Hardware Installation Guide
• 1-Port ADSL WAN Interface Card Configuration
• Configuring a Single-Port Ethernet WIC on a Cisco 1700 Series Router
• Troubleshooting the 1700 Router
• Troubleshooting the 2600 Router
• Troubleshooting the 3600 Router

PC Wholesale carries a full line of Cisco Original and third party DRAM and Flash memory for every Cisco router, firewall and switch.  Search our Cisco Memory section to find your model and see the available upgrade options.

There are several different methods available for configuring your Cisco router. It can be done over a network using a TFTP server, through the boot up menu interface, or the menu interface provided by using the setup command. If you have only just turned on your Cisco router, it will not be configured in any way. If you are new to configuring routers, you should start by checking out the show command. Use the enable command first, try multiple show commands next, and then study the results.

To begin the configuration of your Cisco router, begin by entering configuration mode by entering the config command while in parent mode. In this mode, you can set system wide options also known as global configurations. The first thing you should do is name your router by using the hostname command. This will help you to more readily identify it. Other options you can perform while in global configuration mode include designating the DNS server and setting the password for privileged mode. Your commands will not be entered until you hit control-z. You can do this after each command you enter, or simply when you’ve finished a string of commands to set all of them at once.

Next, look at how you can configure Cisco router interfaces. This is a very straightforward and simple technique that can be accomplished by using the media type slot#/port# command. The ‘media type’ portion of the command refers to the type of media that the port is an interface for. The slot# is applicable only to routers that have slots for installing modules. The port# refers to the port in reference to the other ports available in the module. If your router does not have slots, than your command will be simply ‘media type port#.’

You should know that IP routing is automatically enabled for Cisco routers. If it has been disabled, you can turn it back on by entering ‘config’ mode and entering the ip routing command. A router may assign packets using one of two methods. The first involves the administrator assigning static routes, and the second involves using a dynamic routing protocol. Static routes are generally used for simple networks. Routing protocols, on the other hand, are particularly complex and enable routers to learn the routes that are available to them.

If, in the process of configuration, you discover you need more memory, PC Wholesale carries a full line of Cisco memory for every Cisco router.

The Cisco Technical Support web site contains a wealth of information to help troubleshoot any router issues you might have. Three of the most common are router interface and module issues, router crashes, and router hangs. Each are discussed briefly below with links to detailed information.

Router Interface and Module Issues

The majority of Cisco routers are modular access devices with multiple slots that allow the various network modules to connect to them. The follow are some of the more common problems with router modules:

• Module is not recognized
• Router won’t boot
• Router crashes
• Router hangs

The following document on the Cisco Technical support sight addresses the basic steps required to identify and troubleshoot module issues: http://www.cisco.com/en/US/products/hw/modules/ps2641/products_tech_note09186a008076b147.shtml

Router Crashes

A router crash, or “system crash’, results when a router restarts itself after detecting an unrecoverable error.

When a router crashes, it is critical to collect as much information about the crash as possible before manually reloading or power-cycling the router. Once that is done, all stored data is lost.

The following document on the Cisco Technical support discusses the various types of crashes and how to troubleshoot them: http://www.cisco.com/en/US/products/hw/iad/ps397/products_tech_note09186a00800b4447.shtml

Router Hangs

A router will hang, or appear to stop working, when a system is non-responsive to the console or from network-sent queries, and is generally caused by one of two things:

• Console does not respond
• Traffic does not go through

The following document on the Cisco Technical support site address the cause of router hangs and offers suggestions on how to eliminate them: http://www.cisco.com/en/US/products/hw/routers/ps359/products_tech_note09186a0080106fd7.shtml

At PC Wholesale, we guarantee compatibility for all third party Cisco memory modules, many of which are built to exceed Cisco’s specifications. Also, all third-party memory sold by PC Wholesale has a lifetime warranty – Cisco OEM/Original memory is only under warranty for 90 days. In addition, the cost of third party memory can be considerably less than Cisco Original/OEM memory.