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Cisco Router Commands
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Routing is a process of
moving the data (packets) through an inter network. Routing performs the two
basic tasks. Define the paths for a packet and then forward the packets on
the basis of defined paths. Routing can also be defined as the communication
between two or more logically and physical networks and this communication
(packet transfer) is brought by a router.
You can connect to a Cisco IOS
Router either directly or remotely. For the first time when the device is
not configured yet, you usually connect directly with a console cable via
the CON port or remotely by dialing into a model connected to the AUX port.
These are called “out-of-band” connection methods. After you configure the
router and assign IP addresses to its interfaces, you can connect to the
router from the network with an “in-band” connection method using Telnet or
SSH.
Router Components
RAM
Random-Access Memory similar to the function as RAM in PCs. This is where
the IOS runs its processes. It also contains the running configuration,
routing and other tables as well as packet buffers.
ROM
This Read-Only Memory stores a older 'lite' IOS used to boot the router for
the very first time, or when the Flash memory is erased or corrupted.
FLASH
This piece of 'flash-able' memory stores the IOS image, the operating system
of the router.
NVRAM
In contradiction to normal RAM, Non-Volatile Random-Access Memory is a
special type of memory that doesn't lose its content when the router's power
is turned off. It stores the startup configuration and the configuration
register.
ROM, RAM, NVRAM and of course flash memory can be slightly confusing if you
are a new learner. Knowing that everything has its place can simplify the
learning process and take the guesswork out of all of the similarities. Each
differential has its own meaning and own terms as to the function it
provides to assist and make the motherboard of your computer a true work
horse!
- Read only Memory means ROM. This basically means that this
is the read only memory for your computer. The Rom has the
complex job of storing the operating system components and
software, storing the routers bootstrap program upon startup,
the systems operating software and POST diagnostic systems
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- Flash is the memory in your computer that stores the Cisco
images that are based in your computer. This ROM can be
reprogrammed and erased easily and safely. Your internet router
stores this information when you reload and shut down your
computer system. Random Access Memory is also called RAM. A
Cisco router typically keeps important operational information
about your computer such as routing tables and running files
like the configuration file. Sometimes Random access memory can
be lost when the router is being powered on or off.
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- Non volatile RAM is referred to as NVRAM, it is strictly
considered as being non volatile meaning that it information
stored can not be lost when a power outage is committed or when
the power is turned off or on. NVRAM attaches the running
configuration file.
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- When the RAM is running a configuration file, NVRAM puts the
configuration file on hold, if the NVRAM is emptied at the time
the router happens to reload the computer user is then prompted
to enter a setup mode for safety purposes.
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Config register
The NVRAM has a special location that contains the 16-bit configuration
register. Every time the router boots it reads this value. The config-register
value is a hexadecimal value ranging from from 0x0000 to 0xFFFF and can be
set byusing the config-register command. The most
important portion of the configuration register to understand for the exam
is the boot field (bit 0 through 3, hexadecimal range
0x0000-0x000F). The boot field value is used to specify from which location
the IOS image should be loaded or bypassed even during startup.
Boot field Meaning
0x0 The router will enter ROM monitor mode and remain at the system
bootstrap prompt.
0x1 The IOS image stored in ROM will be loaded.
0x2-0xF The router will boot as normal and load the default IOS image stored
in Flash and enables boot system commands.
Show Commands - Cisco
Routers
Show version -
software version, config files, boot images, config register, basic
config of
router
Show ipx interface - status, ipx rip and
sap received/sent, ipx access-lists
Show ipx route - ipx routing table
Show ipx
servers -
server list (name, port, hops, type of service)
Show ipx traffic - number/type of packets, RIP and SAP packets
Show protocol - ipx addresses of an interface, IP addresses and routing
protocol
Show ip protocol - routing update times, networks active on, neighbour
routers, administrative distances, AS number
Show access-lists - shows standard and extended access-lists on all
interfaces
Show access-list 101
Show ip interface - IP addresses, masks, MTU, access-lists, split horizon,
ICMP, CDP status, NAT statistics, LMI info, DLCIs
Show interface serial 0 - shows bandwidth, MTU, keepalives
Show ip route - ip routing table
Show cdp neighbor - deviceID, local intf, holdtime, capability, platform,
remote portID
Show cdp entry * - IP address of neighbour, protocol info, platform,
capability, portID, holdtime, same info as show version, neighbour device
ID, local interface
Show cdp neighbor detail - same as above also IP address, version info
Show cdp traffic - info on traffic and errors
Show cdp interface - encapsulation, timer, holdtime for each intf
Show controllers serial 0 - shows DTE/DCE connections, buffer size,
collisions, mac address
Show host(s) - shows hostname to IP resolution of hosts
Show session(s) - shows connections to a remote device
Show users - shows connections to your router, port and time connected
Show frame-relay lmi - lmi errors and lmi type
Show frame-relay pvc - all configured PVC's, DLCI numbers, status of
connections, No. of BECN/FECN
Show frame-relay pvc 16
Show frame-relay map - ip to dlci mappings
Show run - display router config (RAM), configured PVCs, ACLs.
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Show Commands -
1900 Switch
Show mac-address-table
Show run
Show ip - like ipconfig
Show port system - shows switching method
Show vtp
Show trunk A allowed-vlans - shows which VLANS allowed on trunk link
Show vlan-membership
Show vlan 2
Show vlan - verify VLAN config
Show history - shows last 10 commands entered by default
Show terminal - shows terminal config + history buffer size
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General Router Commands
Banner exec - for activation or incoming vty
Banner incoming - displayed on reverse telnet sessions
Banner login - displayed on all connected terminals. Displayed before
MOTD banner but before login prompts
Bfe - manual emergency mode setting
Clear counters - clears counters on all interfaces
Clear frame-relay-inarp - clears dynamic mappings
Clear line 1 - clears vty 1 connection to a remote router
Clock set 10.30.10 28 may 2002
Config-register 0x2102 - changes config register
Copy flash tftp
Copy tftp flash - copies IOS image from tftp server default directory to
router flash
Disable - to get back to user mode from privileged
Disconnect 1 - clears a connection to a remote router
Enable - to get into privileged mode
Enable last-resort - define enable action if no tacas servers respond
Enable use-tacas - tells the router to authenticate passwords through a
tacas server
Encapsulation isl 3 - encapsulates ISL frame-tagging for VLAN 3 on an
interface
Exec timeout 0 1 - sets console timeout to 1 second
Exec-timeout 0 0 - sets exec timeout to never timeout
Exec-timeout 1 0 - set exec timeout to 1 minute
Ip domain-lookup - enables DNS (use no form to stop this)
Ip domain-name nikmakris.com - appends domain name to hostname (required
for DNS)
Ip host nik 172.17.1.63 - adds to host table (up to 8 ip addr)
Ip name-server - sets ip address(es) of DNS servers
Lock - locks the terminal
Logging synchronous - stops console messages overwriting commands
Logout - to logout of the router
Media-type 100BaseX - sets media type
Mrinfo - request neigbour and version information from a multicast
router
No login - sets line, vty ports not to prompt for login info
Passive-inteface s0 - disables routing updates on interface (Global
command) - they are not sent out this interface but they are still
received.
Ping ipx 40.0000.0c8d.5c9d
Service password-encryption - encrypts passwords (Global command)
Terminal monitor - needed to view debug commands from telnet session
Terminal history size 50 - sets command history to 50 lines
Tftp-server system <image name> - Make router a tftp server
Continued
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