| A | B |
|---|
| External router configuration sources | 1) from the console terminal (a computer connected to the router through a console port) during its installation; 2) via modem by using the auxiliary port; 3) from Virtual Terminals 0-4, after it has been installed on the network; 4) from a TFTP server on the network |
| Internal router's configuration components | RAM/DRAM; NVRAM; Flash; ROM; Interfaces |
| RAM/DRAM | stores routing tables, ARP cache, fast-switching cache, packet buffering (shared RAM), and packet hold queues; RAM also provides temporary and/or running memory for a router's configuration file while the router is powered; RAM content is lost during a power down or restart |
| NVRAM | non-volatile RAM stores the router's backup/startup configuration file; NVRAM content is retained during power down or restart |
| Flash | erasable, reprogrammable ROM that holds the operating system image and microcode; Flash memory enables software updates without removing and replacing processor chips; Flash content is retained during power down or restart; Flash memory can store multiple versions of IOS software |
| ROM | contains power-on diagnostics, a bootstrap program, and operating system software; software upgrades in ROM require removing and replacing pluggable chips on the CPU |
| Interfaces | network connections on the motherboard or on separate interface modules, through which packets enter and exit a router |
| Router modes | user EXEC mode; privileged EXEC mode; setup mode; global configuration mode; other configuration modes; RXBOOT mode |
| user EXEC mode | This is a look-only mode in which the user can view some information about the router, but cannot make changes. |
| privileged EXEC mode | This mode supports the debugging and testing commands, detailed examination of the router, manipulation of configuration files, and access to configuration modes. |
| setup mode | This mode presents an interactive prompted dialog at the console that helps the new user create a first-time basic configuration. |
| global configuration mode | This mode implements powerful one-line commands that perform simple configuration tasks. |
| other configuration modes | These modes provide more detailed multiple-line configurations. |
| RXBOOT mode | This is the maintenance mode that you can use, among other things, to recover from lost passwords. |
| show version | displays the configuration of the system hardware, the software version, the names and sources of configuration files, and the boot image |
| show processes | displays information about the active processes |
| show protocols | displays the configured protocols; shows the status of all configured Layer 3 protocols |
| show memory | shows statistics about the router's memory, including memory free pool statistics |
| show stacks | monitors the stack use of processes and interrupt routines and displays the reason for the last system reboot |
| show buffers | provides statistics for the buffer pools on the router |
| show flash | shows information about the Flash memory device |
| show running-config | (write term on Cisco IOS Release 10.3 or earlier) -- displays the active configuration file |
| show startup-config | (show config on Cisco IOS Release 10.3 or earlier) -- displays the backup configuration file |
| show interfaces | displays statistics for all interfaces configured on the router |
| 2 most used Cisco IOS software EXEC commands | running-config & show startup-config |
| Cisco Discovery Protocol (CDP) | single proprietary command that enables network administrators to access a summary of what the configurations look like on other directly-connected routers. CDP runs over a data link layer |
| show cdp neighbors command | display the CDP updates on the local router |
| show cdp interface, | display the values of the CDP timers, the interface status, and the encapsulation used by CDP for its advertisement and discovery frame transmission. Default values for timers set the frequency for CDP updates and for aging CDP entries. These timers are set automatically at 60 seconds and 180 seconds, respectively. If the device receives a more recent update, or if this hold-time value expires, the device must discard the CDP entry. |
| show cdp entry {device name} | display a single cached CDP entry |
| Testing process that uses the OSI model | telnet, ping, trace, show ip route, show interfaces and debug |
| Telnet | a virtual terminal protocol that is part of the TCP/IP protocol suite, allows connections to be made to hosts. You can set a connection between a router and a connected device. Telnet allows you to verify the application-layer software between source and destination stations. This is the most complete test mechanism available. A router can have up to five simultaneous incoming Telnet sessions. |
| ping | sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functioning. |
| trace | The trace command takes advantage of the error messages generated by routers when a packet exceeds its Time To Live (TTL) value. The trace command sends several packets and displays the round-trip time for each. The benefit of the trace command is that it tells which router in the path was the last one to be reached. This is called fault isolation. |
| show ip route | determine whether a routing table entry exists for the target network. |
| show interfaces serial | ommand output is display of the line and data link protocol status |
| show interfaces | display the statistics as shown in the figure. The statistics reflect router operation since the last time the counters were cleared |
| clear counters | reset the counters to 0. By starting from 0, you get a better picture of the current status of the network |
| debug privileged EXEC command | starts the console display of the network events specified in the command parameter |
| debug CAUTION | Be very careful with this tool on a live network. Substantial debugging on a busy network will slow down the network significantly. Do not leave debugging turned on; use it to diagnose a problem, and then turn it off.) |
