cisco router configuration basics

1
cisco router configuration basics
2
overview

• router configuration controls the operation of
  the router
• interface address and netmask
• routing information (static or dynamic)
• booting and startup information
• security (passwords)

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overview

• configuration statements have different contexts
• global
• enable-password mysecret
• interface
• interface ethernet0
• ip address 195.176.118.254 255.255.255.0
• router
• router ospf 1
• network 195.176.118.0 0.0.0.255 area 0

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global configuration

• global configuration statements are independent
  of any particular interface or routing protocol,
  e.g.
• hostname myrouter
• enable-password mysecret
• service password-encryption
• logging facility local0
• logging 195.176.118.42

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global configuration

• ip-specific global configuration statements
• ip classless
• static route creation
• ip route 195.176.118.0 255.255.248.0 195.176.31.1

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interface configuration

• interfaces are named by type and position e.g.
• ethernet0, ethernet1,... ethernet5
• serial0, serial1 ... serial3
• and can be abbreviated
• ethernet0 or eth0 or e0
• serial0 or ser0 or s0

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interface configuration

• ip address and netmask configuration, using
  interface commands (interactive configuration
  example, showing prompts)
• routerconfig terminal
• router(config)interface e0
• router(config-if)ip address 195.176.118.254
  255.255.255.0
• router(config-if)no shutdown
• router(config-if)Z
• router

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There are two modes on a cisco router

• normal mode
• routergt
• enable mode
• routergt enable
• router config terminal

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interface configuration

• administratively enable/disable the interface
• router(config-if)no shutdown
• router(config-if)shutdown
• (config-if) no ip proxy-arp
• (config-if) no ip directed broadcast
• (config-if) no ip redirect
• description
• description 128k circuit 123-ABC to hotel

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where is the configuration?

• router always has two configurations
• running configuration
• in RAM, determines how the router is currently
  operating
• is changed by using the configuration command
• to see it show running
• startup configuration
• in NVRAM, determines how the router will operate
  after next reload
• is changed using the copy command
• to see it show startup

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where is the configuration?

• can also be stored in more permanent places
• external hosts, using TFTP to move it around
• in flash memory in the router
• copy command is used to move it around
• copy run start
• copy run tftp
• copy start tftp
• copy tftp start
• copy flash start
• copy start flash

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looking at the configuration

• use show running-configuration to see the
  current configuration
• use show startup-configuration to see the
  configuration in NVRAM, that will be loaded the
  next time the router is rebooted or reloaded

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changing the configuration

• configuration statements can be entered
  interactively at the console, or in a telnet
  session,
• or, edited in a text file and uploaded to the
  router at a later time
• some configuration statements, especially access
  lists, are very difficult to work with
  interactively, so editing and uploading the file
  is the only practical way to work
• also allows version control and auditing changes

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interactive configuration

• can use direct serial connection to console port,
  or
• telnet to vtys (virtual terminals), or
• modem connection to aux port
• in every case, changes are made (almost)
  immediately, to the running configuration

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interactive configuration

• enter configuration mode, using configure term
• prompt gives a hint about where you are
• routerconfigure terminal
• router(config)hostname K-rtr
• K-rtr(config)ip classless
• K-rtr(config)ip subnet-zero
• K-rtr(config)interface ethernet3
• K-rtr(config-if)ip address 195.176.118.253
  255.255.255.0
• K-rtr(config-if)no shutdown
• use the no command to nullify command given
• (config-if) no ip addr 195.176.118.253
  255.255.255.0

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storing the configuration on a host

• requires tftpdon a unix host destination file
  must exist before the file is written and must be
  world writable...
• copy run tftp
• K-rtrcopy run tftp
• Remote host ? 195.176.118.42
• Name of configuration file to write
  K-rtr-confg? /usr/local/tftpd/K-rtr-confg
• Write file /usr/local/tftpd/K-rtr-confg on...
  host 195.176.118.42? confirm
• Building configuration...
• Writing /usr/local/tftpd/K-rtr-confg !!OK

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restoring the configuration from a host

• use tftp to pull file from unix host, copying
  to running config or startup
• K-rtrcopy tftp start
• Address of remote host 255.255.255.255?
  195.176.118.42
• Name of configuration file K-rtr-confg?
• Configure using K-rtr-confg from 195.176.118.42?
  confirm
• Loading K-rtr-confg from 195.176.118.42 (via
  Ethernet0) !
• OK - 1005/128975 bytes
• OK
• K-rtr reload

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getting help

• IOS has a built-in help facility use ? to get
  a list of possible configuration statements
• ? after the prompt lists all possible commands
• router?
• ltpartial commandgt ? lists all possible
  subcommands, e.g.
• routershow ?
• routershow ip ?

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getting help

• ltpartial commandgt? shows all possible command
  completions
• routercon?
• configure connect
• this is different (space before ?)
• routerconf ?
• memory Configure from NV memory
• network Configure from a TFTP
  network host
• overwrite-network Overwrite NV memory from
  TFTP... network host
• terminal Configure from the terminal
• ltcrgt

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getting help

• this also works in configuration mode
• router(config)ip a?
• accounting-list accounting-threshold
  accounting-transits address-pool alias as-path
• router(config)int e0
• router(config-if)ip a?
• access-group accounting address

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getting help

• can explore a command to figure out the syntax
• router(config-if)ip addr ?
• A.B.C.D IP address
• router(config-if)ip addr 169.222.64.1 ?
• A.B.C.D IP subnet mask
• router(config-if)ip addr 169.222.64.1
  255.255.255.0 ?
• secondary Make this IP address a secondary
  address
• ltcrgt
• router(config-if)ip addr 169.222.64.1
  255.255.255.0
• router(config-if)

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getting lazy help

• TAB character will complete a partial word
• router(config)intltTABgt
• router(config)interface etltTABgt
• router(config)interface ethernet 0
• router(config-if)ip addltTABgt
• router(config-if)ip address ... 195.176.118.1
  255.255.255.0
• not really necessary partial commands can be
  used
• routerconf t
• router(config)int e0
• router(config-if)ip addr 195.176...

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getting lazy

• command history
• IOS maintains short list of previously typed
  commands
• up-arrow or P recalls previous command
• down-arrow or N recalls next command
• line editing
• left-arrow, right-arrow moves cursor inside
  command
• D or backspace will delete character in front
  of cursor