Router Lab Reference Guide

Transcription

1 Router Lab Reference Guide 1 PURPOSE AND GOALS The routing lab allows testing different IP-related protocols and solutions in a close to live environment. You can learn how to configure Cisco routers and test different protocols in various topologies. This document is intended to serve as a basic source of knowledge about: router lab topology, remote access to the lab facilities, Cisco IOS command line, basic router configuration. 2 LAB OVERVIEW In context of the exercises related to this course, the router lab consists of: a terminal server (a host providing access to individual router consoles), 5 Cisco 26xx series routers, equipped with V.35 2 Mbps serial interfaces and 100 Mbps Fast Ethernet interfaces, running Cisco IOS version 12.4, gateway switch (ztit-gateway, IP address: ). The physical links between the routers are fixed (see Figure 1). By changing the state of the different interfaces you can activate or deactivate the individual physical links, adapting the network topology to the requirements of the specific exercise. By configuring loopback interfaces on the routers it is possible to simulate one or more virtual subnets behind each individual route. 3 REMOTE ACCESS Remote access to the Router Lab requires active reservation of resources that should be done beforehand using the Resource Reservation System available at: The system allows reservation of timeslots for attempting the Router Lab exercises. Using the system itself requires an active account that should have been granted by the exercise administrator (for information ask the lecturer of the relevant course). The system and reservation procedures are described in detail in the Resource Reservation User Guide that should be available as a document complementary to this one. Provided that you already have access to the Reservation System, the router lab can be accessed remotely from any PC equipped with Internet access and an ssh client. This is accomplished by opening an ssh session with the gateway server that allows accessing the internal network of the Faculty. The gateway server is a linux machine visible from the public Internet at the IP address and listens for incoming ssh sessions at port number 22. Institute of Telecommunications, Warsaw University of Technology

2 The credentials to login to the gateway server are granted only for the time period that was previously reserved to attempt the given exercise and are sent via at the beginning of this period. After successful login to the gateway server, it is possible to access routers console ports via the terminal server. You can connect to a specific router by opening a telnet session to a specific TCP port on the terminal server. The procedure is described in detail in the following section. Internet Ethernet switch S1 gateway server Terminal server R1 port 2101 R2 port 2102 R3 port 2103 R4 port 2104 R5 port 2105 Fig. 1. Working topology of the Router Lab Institute of Telecommunications, Warsaw University of Technology

3 4 ROUTER CONSOLE ACCESS After logging to the gateway server via the ssh session, you can access the routers via the terminal server. The IP address of the terminal server should be provided by the lab exercise supervisor. Since telnet sessions to the terminal server are not ended when you log out of the router, you have to make it possible to escape out of each telnet session to end it. By adding the option e to the telnet command you set an escape character for this session. In this document we use # as the escape character. To initiate a telnet session to a console port via the terminal server you should therefore use the following command: >> telnet e# <terminal server IP> <TCP port> When you close the router console (by the quit command), you are entering the state when hitting carriage return (Enter) resumes the telnet session with the console and entering the escape character (in this example the # sign) gets you out of the session, to the telnet service command prompt. Entering the close command allows you to close the telnet session and return to the OS command prompt. The terminal server is configured such that each router console corresponds to an individual TCP port: R1 = TCP port 2101 R2 = TCP port 2102 R3 = TCP port 2103 R4 = TCP port 2104 R5 = TCP port 2105 To connect to R1 s console port you should then (from within an ssh session with the gateway server) establish a telnet session to the terminal server IP address and TCP port 2101: >> telnet e# <terminal server IP> THE ROUTER SOFTWARE 5.1 IOS The routers run Cisco IOS. There is an abundance of in-depth information related to the IOS in the Internet, so here only a very brief introduction is given. IOS is the Cisco routers operating system. You control IOS, and thereby the router, using IOS command line interface, in short the CLI. 5.2 COMMAND COMPLETION AND HELP In most cases it is not necessary to write the IOS commands in full. As soon as there are enough characters so that the CLI can differentiate between commands available in the specific context, you can stop entering characters. If you are not sure which commands are available you can always enter a? sign for help. This is also true if you want to check subcommands. You can also use the TAB key for command completion. Institute of Telecommunications, Warsaw University of Technology

4 5.3 MODES IOS has several command levels or modes. Depending on mode you can use different commands. When you connect to a router you enter the EXEC mode. The command you will use most in this mode is the show command. You can also use the ping command, or the telnet command. In EXEC mode the command prompt ends with a >: R1> To be able to control the router you must change the mode to PRIVILEGED. You can do this by entering the enable command in EXEC mode. In the PRIVILEGED mode the command prompt ends with a #: R1# You can return to EXEC mode from PRIVILEGED mode with the command exit. Another mode is the CONFIG mode (see Section 5.5). 5.4 CONFIGURATION The router has two configuration storages. The first one is the startup-config. This configuration is stored in non-volatile memory, and is read into running-config memory when the router starts up or reboots. The running-config memory contains is the configuration that is used when the router is up and running. When you are in CONFIG mode and enter configuration commands you change the running-config immediately, thereby changing the behavior of the router. You can copy the running-config to startup-config memory by using copy running-config startup-config Doing so at the beginning of the exercise will create the startup-config and allow reverting to the initial state by typing: configure replace nvram:startup-config Note! Do not use the reload command to revert to the default configuration as you may loose access to the router console afterwards. 5.5 THE CONFIGURE COMMAND To enter CONFIG mode you issue the config command. This command takes parameters, and in our case you want to enter configuration commands from the terminal. So the command should look like this: or in short just # configure terminal # conf t Once in CONFIG mode remember that each configuration command you enter is activated immediately. It is easy to cut off the branch you are sitting on, trust me. In our lab, though, you are accessing the router via the console port which is very hard to shut down. Institute of Telecommunications, Warsaw University of Technology

5 Each function in the router can be set or unset. To set a function you just use the specific configuration command. To unset a function you write no in front of the same command. All functions have a default status, for most of them this state is unset. The default state is not printed in the configuration listing. So those few commands that have the state set as the default state, you will not see in the configuration print out. They will only be listed if you have unset them, that is they will show in the listing with a no in front of them and will be unseen again if you activate that function. CONFIG mode has several sub modes, for instance the interface configuration sub mode. You enter this mode by typing the interface configuration command: or in short just (config)# interface fastethernet 0/0 (config)# in fa0/0 In configure interface sub mode you can assign the interface an IP address. Use the command ip address <ip address> <mask>. In this sub mode you can also open and close individual interfaces. To close an interface you use the shutdown command. And in consequence of what was said above, you open an interface with the command no shutdown. You can also create and delete virtual interfaces, so called loopback interfaces, in the configure interface sub mode. To create a new loopback interface just type the configure command interface loopback <interfacenumber>. You can exit from CONFIG mode or any sub mode to PRIVILEGED mode by typing ctrl Z. To exit from a sub mode or from the CONFIG mode use the exit command. 5.6 THE DEBUG COMMAND Another nifty command is the debug command. In general it is dangerous to use, since by issuing this command you might end up in a situation where all packets going through the router are displayed on the console terminal. This may has severe impact on the router throughput. But in the router lab there is normally very little actual traffic between the routers. You can debug nearly anything you want, from each single IP-packet to routing announcements sent between the routers. To see the output from the debugging you must direct it to the terminal console that you are connected to. Use command terminal monitor. To turn on debugging you issue command debug <parameter >. To turn it off it is often best to use no debug all. 5.7 THE QUIT COMMAND To end a console session you use the quit command. Note that this command does not end the telnet session to the terminal server (see Section 4). 5.8 THE SHOW COMMAND The show command is the one that you will use the most. All parameters of the router can be inspected with this command. Here are some typical uses of this command that you will need. show running-config With this command you inspect the running-configuration. It must be given in PRIVILEDGED mode. show interface Institute of Telecommunications, Warsaw University of Technology

6 With this command you inspect the current status of an interface. You can enter an interface name if you don t want to list them all. show IP interface brief With this command you get a list of all the router s interfaces with IP addresses. show IP protocol This command gives you information on parameters and status of routing processes running on the router. show IP route You show the router s current forwarding table with this command. If you want to see a routing table for the particular one of perhaps several routing protocols, use the command show ip route <routing protocol>. show CDP neighbor Cisco Discovery Protocol is Cisco s proprietary protocol used to exchange information between Cisco equipment. It allows retrieving information on which neighbors are connected to a device, and also some basic information about them. This command is a good way to check your connections. If you add the parameter detailed as a suffix to this command you will get a lot of information. 5.9 THE PING AND TRACEROUTE COMMANDS Both ping and traceroute are available tools in IOS. In their normal form they take the remote host as parameter. Example: ping traceroute Since a router has several interfaces, i.e. more than one, there is a minor issue here: Which of the several addresses of a router should be used as a source address? All functions that make use of IP packets, including ping and traceroute, use the interface closest to the remote host, and therefore the IP address of this interface is used as source address. In our lab we will meet situations where this is not what we want. We might want to check connection with a router loopback interface as source. In PRIVILEDGED mode you can use the extended version of ping and traceroute. Just enter the ping or traceroute command without any parameters, and you will have several ways to control these commands, like number of packets sent, packet size, and more. Answer yes to Extended commands question and you will have the possibility to declare source interface or source IP address. In the latter case the IP address must be one of the router s own IP addresses. Note! Serial interfaces on the routers in the lab do not answer to ping if both interfaces on the serial link are not configured correctly. This is especially valid for the IP addresses; both interfaces on the serial link must have IP addresses in the same subnet before any of them answers to ping requests. Institute of Telecommunications, Warsaw University of Technology

7 6 SUGGESTED ADDRESS SPACE The router lab is only connected to the global internet in one point, and that is the gateway server. Since there is no routing or bridging performed by the gateway server, the lab can be said to have no connection at all to the outside world. You therefore are free to use any IP addresses you want in the lab. Nevertheless, it is strongly advised to use private addresses. The suggested address space to use in the lab is ADDITIONAL INFO 7.1 HOW TO EXIT A TELNET SESSION THAT IS STUCK If you cannot exit from a telnet session for any reason, follow these steps. Open a new ssh session to the gateway server and find the PID of the stuck telnet session with the ps command. Kill the stuck telnet session with the kill command (use the PID you found with the ps command). Close the extra ssh session. 7.2 HOW TO CONFIGURE A SERIAL LINK THAT IS USING NULL MODEM CABLES A serial link using V.35 has the need for a synchronization clock. In our lab we use null modem cables as serial links and thus one of the routers has to be responsible for the clocking. Because of cabling configuration, each interface serial 0/0 has to be configured with the clock rate: R1 interface Serial0 R2 interface Serial1 bandwidth 2000 bandwidth 2000 clock rate In this example the link is connected between R1 serial interface 0 and R2 serial interface 1. The interface in R1 produces a clock with the bit rate 2 Mbps. 7.3 OTHER HINTS Router interfaces are inactive by default. After proper configuration they have to be activated using no shutdown command. During lab exercises you are expected to observe the results of the debug command. Please note that to do so you need to issue the terminal monitor command in the PRIVILEGED mode. Command lines starting from show and debug work properly only in the PRIVILEGED mode (indicated by the # sign next to the router name). After configuring a router and routing protocol it is advised to check the validity of configuration by reviewing the config file (show running-config) and router s routing table (show ip route). Institute of Telecommunications, Warsaw University of Technology