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Chap 4 Router Components Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology [email protected] http://www.cse.dlit.edu.tw/~andres Overview The correct procedures and commands to access a router Examine and maintain its components Test its network connectivity Router Components External router configuration sources Internal router's configuration components RAM for working storage in the router Router modes External router configuration sources The console terminal A computer connected to the router through a console port (initial) Via modem by using auxiliary port Virtual Terminals 0-4 (5 connections) From a TFTP server on the network RAM for working storage When you turn a router on, the ROM executes a bootstrap program This program performs some tests, and then loads the Cisco IOS software into memory RAM for working storage The command executive, or EXEC, is one part of the Cisco IOS software EXEC receives and executes commands you enter for the router RAM - Configuration Store an active configuration file and tables of network maps and routing address lists You can display the configuration file on a remote or console terminal RAM - Configuration A saved version of configuration file is stored in NVRAM It is accessed and loaded into main memory each time a router initializes RAM - Configuration The configuration file contains global, process, and interface information that directly affects the operation of a router and its interface ports RAM - OS An OS image cannot be displayed on a terminal screen An image is usually executed from the main RAM and loaded from one of several input sources RAM - OS The OS is organized into routines that handle the tasks associated with different protocols, such as data movement, table and buffer management, routing updates, and user command execution Router Show Commands Examining router status by using router status commands The show running-config and show startup-config commands The show interfaces, show version, and show protocols commands Displays configurable parameters and real-time statistics related to all interfaces Displays information about the Cisco IOS software version shows the global and interface-specific status of any configured Level 3 protocols Router's Network Neighbors Gaining access to other routers by using CDP Showing CDP neighbor entries A CDP configuration example Showing CDP entries for a device and CDP neighbors Cisco Discovery Protocol (CDP) A single proprietary command Access a summary of the configurations on other directlyconnected routers Runs over a data link layer (Layer 2) Support different network layer protocols CDP When a Cisco device that is running Cisco IOS boots up, CDP starts up automatically, which then detect neighboring Cisco devices that are also running CDP Showing CDP neighbor entries The primary use of CDP is to discover platforms and protocols on your neighboring devices show cdp neighbors command Display the CDP updates on the local router CDP Information device identifiers -- host name and domain name address list -- at least one address for SNMP, up to one address for each supported protocol CDP Information port identifier -- Ethernet 0/1 and Serial 0 capabilities list -- source route bridge and router version -- show version platform -- Cisco 7000 A CDP configuration example A router caches any information it receives from its CDP neighbors If a subsequent CDP frame has changed, the router discards the older information and replaces it with the new information Display the values of the CDP timers, the interface status, and the encapsulation used by CDP for its advertisement and discovery frame transmission Showing CDP entries for a device and CDP neighbors show cdp entry {device name} Display a single cached CDP entry show cdp neighbors Display the CDP updates received on the local router The amount of elapsed time since the CDP frame arrived Basic Networking Testing Use the OSI model telnet, ping, trace show ip route show interfaces serial show interfaces and clear counters debug Telnet Verify the application-layer software between source and destination stations A router can have up to five simultaneous incoming Telnet sessions Initiate a session from Denver: Denver> connect paris Denver> paris Denver> 131.108.100.152 Resume a session (enter session number or name): Denver>1 Paris> End a session: Paris> exit ping command Test whether protocol packets are being routed Send a packet to the destination host and then waits for a reply packet Evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functioning ping command Exclamation points (!) Each successful echo Periods (.) Router timed out Uses the ICMP (Internet Control Message Protocol) trace command Find where data is being sent in your network Tests each step along the way Takes advantage of the error messages generated by routers when a packet exceeds its Time To Live (TTL) value trace command Fault isolation Tells which router in the path was the last one to be reached If one of these routers had been unreachable, you would have seen three asterisks (*) instead of the name of the router show ip route command Routing table Determine whether a routing table entry exists for the target network show interfaces serial command Display of the line and data link protocol status Interface has two pieces The hardware: cables, connectors, and interfaces. The software: keepalive messages, control info., and user info. show interfaces and clear counters commands show interfaces command to display the statistics clear counters command to reset the counters to 0 Checking real-time traffic with debug debug privileged: starts the console display of the network events terminal monitor: forward debug output to your Telnet session undebug all command (or no debug all) to turn debugging off debug Be very careful with this tool on a live network. Substantial debugging on a busy network will slow down the network Do not leave debugging turned on; use it to diagnose a problem, and then turn it off Summary Configurable components show commands CDP: show entries about neighbors Telnet ping, trace, and debug