|
RE:ddd
An OS image cant be displayed from a term screen.. Image is usually executec from main RAM & loaded from 1 of severAL input sources.. The OS is organizd into routines that handle tasks assoc w differnt protocols suach as data movement, table and buffer management, routing upDAtes and user command execution
SIX ROUTER MODES;:
Wheyther accessed from a console or telnet session through a tty port, a router can be placed in several modes, each providing different functions:
USER EXEC MODE; lokk only mode which user can view but not chnge
PRIVLEDGED EXEC MODE; supports debugging & testing commands, detailed exam of router, manipulation of config files and access to config modes
SETUP MODE; presents a prompted dialog mode for first time config of router
GLOBAL CONFIGURATION MODE; implement powerfiyul one line commands that perform simple config tasks
OTHER CONFIGURATION MODES; provide more detailed multi-line configs
RXBOOT MODE; a maintenance mode that yu can use to recover lost passwords
Router Status commands:
Show Version: displays config of sys hardware, software version, names and sources of config files and boot image
SHOW PROCESSES; displays info about active processes
SHOW PROTOCOLS;displays configured protocols, shows status of all layer3 protocols
SHOW MEM; shows statistica abouyt router's memory, including free memory pools
SHOW STACKS monitoors the stack use of processes and interrupt routines & displays the reason for the last sys reboot
SHOW BUFFERSprovides statistics for buffer pools on router
SHOW FLASH shows info about Flash memory device on router
SHOW RUNNING-CONFIG (write term WTF? Cisco IOS release 10.3 or earlier) - displays active config file
SHOW STARTUO-CONFIG ( show config on IOS 10.3 or earlier) displays backup config
SHOW INTERFACES displays stats for all interfaces configed on router
Show running-config & show startup-config allow an admin to see current config of router and how router will start at next reboot
You can recognize an active config by the words CURRENT CONFIGURATION at the top. U can recognize a backup config file when you see a messahe at top that tells u how much non-volatile memory you have used
Show interfaces Serial - displays configurable parameters & real-time stats related to serial ints
Show Version - command displays info about the Cisco IOS software version that is currently running on rtouter
Show Protocols - EXEC command displays the global and int specific status of any configed lkayer 3 protocol] that is configured on the router
Cisco Discovery Protocol: CDP provides a single proprietary command that enables net admins to access a summary of what the configs look like on other directly connected routers..
CDP runs over a data link layer that connects lower physical media and upper network layer protocols. Because it operates at L2, CDP devices that support different L3 protocols can learn about each other,
On Cisco IOS ver 10.3 or later boots, CDP starts by default and detects neighboring Cisco devices that are lso running CDP. Such devices extend beyong using TCP/IP and include directly-connected Cisco devices regardless of L3 or L4 protocol suite they run
Each router running CDP exchanges info regarding protocol entries with its neighbors. Admins can display results of this CDP info exchange on a console that is connected to a CDP running Router
CDP Show commands
Show device identifiers the routers configured host and somain names if any
Show address list at least one address for SNMP, up to one address for each supported protocol
Show port identifier eg Ethernet 0, Ethernet and Serial 0
Show capabilities list if device acts as a source route bridge as well as a router
Show version
Show platform ie Cisco 7000, 2500
Routers cache CDP info about its neighbors and releases that if any changes occur
The comand Show CDP Interface will display values of CDP timers, int staus, and encapsulation used by CDP for advertising and discovering frame transmission
Default values for timers set freq for CDP updates and for aging CDP timers. If the device receives a more recent update or if thisd hold-time value expiers, the device must discard the CDP entry
Show cdp entry (device name) to display single cached CDP entry. This shows all L3 addresses present in router . The hold time value represents elasped time since CDP frame arrived
Show cdp neighbors to display the CDP updates received on local router. Notice that for each local port the disply shows:
Neighbor device id
Local port type and #
Decremental hold-time value, in seconds
Neighbor device capability code
Neighbor hardware platform
Neighbor remote port type and #
To display the above info as well as info like from show cdp entry use the optional show cdp neighbors detail
Telnet
With Ciscos telnet you do not need to enter command CONNECT or TELNET to est connection, just enter learned hostname
<Ctrl><shift><6><x>
To exit, EXIT or LOGOUT
Basic testing of network should procedd in sequence from one OSI layer to the next.
L7 Telnet
L3- ping
Trace
Show IP route
L321 show interface
A successful Telnet connection indicates that upper layers as well as lower layers are working
When you can telnet one router but not another its usually due to address, naming, or access permission
PING uses ICMP Internet Control Message Protocol
Trace is similar to ping except instread of end to end connectivity, trace tests each step of the way. Trace 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 round trip time for both. It also tells which router on path is last to be reached this is called fault isolation
Trace will continue until it reaches 30 hops or until escaped crtl-#### 6 esc
Network testing at the network layer with the show ip route command
The interface has 2 components - physical and logical
The hardware must make actual connection between devices and the software controls the messages that are passes
|