Preparing for Configuration

There are several steps involved in commissioning a new router. The first is to determine physical configuration. Although any interface card may be placed in any slot, thought should go into how cards are arranged. For example, if you intend to have a large group of routers with more or less identical types and quantities of cards, it is easier to place the cards in a "standard" order. This way, there is no searching to find what card is in which slot. it is simply assumed that a given card will be in a given slot. This leaves less to remember and can cut critical time off diagnosing network problems. Initial configuration is done from the console. There are a few caveats which will be explained later. The console should be connected via a straight through rs232 interface using either a standard rs232 cable or one of the appropriate adaptors provided with the 2501 (Note: the adaptors for the 2500 series routers are proprietary to cisco and do NOT contain standard pin-outs.) The connection operates at 9600 baud, 8 data bits, 1 stop bit and no parity. Boot the router and wait for the "press return to get started" prompt. When the router boots for the first time after being shipped from the manufacturer, you may enter the "setup" dialogue. In general, you don't want to use setup to initialize your router. You may exit out of this when prompts or you can type C-^ (caret), which is the cisco interrupt character, to break out of it. You should end up at a "Router>" prompt. This is an unprivileged access mode known as "User EXEC Mode". There are several levels of access that can be configured within the router. This mode is privilege level 1. (You may use the "show privilege" command to find out what your current privilege level is.) To enter a higher privilege mode, use "enable". The default privilege level is 15. If a password has been set, you will be prompted to enter it at this time. If no password has yet been set, you will not be prompted for a password, and instead immediately gain privileged access. Your prompt will now become "Router#". At that point, you may prepare to enter configuration commands by typing "configure terminal". Your prompt will change to "Router (config)#". To exit the configuration, type "exit" or C-z. Once you are done, you need to store your configuration changes in non-volatile memory. Type "write" from the privileged EXEC prompt (Router#). It will take a few moments to build the configuration file and store it in memory. As mentioned above, there are a few things to watch for when configuring cisco routers. Once logged into a router via a network connection, you cannot "enable" from the network connection if no enable password has been set. One of the most important things to remember is that ALL changes are IMMEDIATE. If you attempt to restart an interface by shutting it down and then turning it back up, if it is the interface you are coming in over, you will never be able to turn the interface back up unless you come in via an alternate path (such as logging in on console or by dialing up to a POP) or power cycle the router. Likewise, when configuring a packet filter, it is a good idea to remove the filter from the associated interface while updating it if at all feasible. This saves you from filtering yourself out of the router and possibly causing significant interruption of services for others. Also, for any given command, with only a few exceptions, placing a "no" in front of the command has the effect of "undoing" that operation.