There are several ways in which a new router can obtain its own IP address and initial configuration file.
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These depend on the presence on the network of another Cisco router, a BOOTP server, or a DNS server.
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If none of these exist on the network then you configure the router manually.
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The Cisco IOS software listens on Ethernet interface 0 for a DNS request to the name ^Rnew-router.cisco.com^r.
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This name is reserved within Cisco IOS for initial router configuration.
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No system will ever have this name, and name servers do not respond to it.
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The New Router DNS request contains the IP address of the device (the PC used to configure the router) that issued the DNS request.
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The Cisco IOS software then uses the ARP protocol to locate an unused IP address near the IP address of the device that issued the DNS request.
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If a machine responds to the ARP probe, the Cisco software tries the next IP address until it receives no response to an ARP call.
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The Cisco software uses the address to which there was no response as the IP address of the router.
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The software sends a DNS reply to the device in answer to the New Router DNS request with the IP address for the router.
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A new router on a network without sources to provide the initial configuration file has no host name, IP address, or interface IP addresses with which to communicate with other network devices.
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You have to configure these settings manually on the router when it's turned on for the first time.
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Depending on the way your network is set up, you can configure a router using one of the following procedures:

• System Configuration Dialog
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• Configuration mode
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• AutoInstall
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If you are unfamiliar with Cisco IOS commands, use the System Configuration Dialog.
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You can use the Configuration mode method if you are familiar with the Cisco IOS commands.
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For information on Cisco IOS commands see the CBT Systems course ^RCisco Router Configuration Basics^r.
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AutoInstall is for automatic installation if you have another router running Cisco IOS software on the network.
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The System Configuration Dialog prompts you to configure the routing protocols and the router interfaces.
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Remember to disconnect all WAN cables from the router if you want to use the System Configuration Dialog.

If WAN cables are connected to the router, the AutoInstall method runs instead.
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The System Configuration Dialog guides you through creating a configuration file by asking a series of questions.
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These questions prompt you to provide the router with a host name, and to assign passwords and IP addresses.
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You assign IP addresses to each required interface.
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Before you configure the interfaces, decide on the interfaces you want to configure, the IP addresses they will have, and the number of bits in the subnet field.
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As in the example shown here, if you don't want to configure a particular interface, just type ^Rno^r to answer the question "Is this interface in use?"
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If you do, press ^UReturn^u to indicate the default answer yes.
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The dialog then asks if you want to configure an IP address on this interface.
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If you press ^UReturn^u for yes, it allows you to enter the IP address on the next line.
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You then enter the number of bits in the subnet field.
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An interface can have one primary IP address or multiple secondary IP addresses.
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Secondary IP addresses on router interfaces are useful for several reasons.
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They allow you to increase the number of hosts supported on a network segment by letting you have two logical subnets using one physical subnet.
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For example, an organization with a class C address that supports 254 hosts on an Ethernet segment now needs to support another 250 hosts.
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A simple way of overcoming this problem is to assign a second class C network address, which yields another 254 IP addresses.
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To do this you will have to configure the Ethernet port with a secondary IP address.
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You can also use secondary IP addresses to

• help you to subnet networks designed
  before subnetting became common
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• create a single logical network from
  subnets on separate networks
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<F>When configuring the serial interfaces, you will be asked if you want to configure an unnumbered IP on this interface.
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Serial interfaces may be unnumbered and still remain capable of IP processing.
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You assign the name of another interface with an IP address in the router to the unnumbered interface.
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The unnumbered serial interface uses the specified IP address as a source address when it generates packets.
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It also uses the assigned interface address to determine which routing processes are sending updates over the unnumbered interface.
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When you are finished configuring the interfaces, the dialog asks if you want to use this configuration.
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The router has a running configuration at this point.
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You can specify other configuration options using the Configure command in Privileged mode.
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When the router has a configuration, but it is not saved to non-volatile RAM (NVRAM), the configuration is referred to as the running configuration.
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The running configuration must be saved to NVRAM so that it will not be lost if the router is switched off or crashes.
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The command Copy Running-Config Startup-Config copies the running configuration to NVRAM.
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At this stage you have configured class B IP addresses, all with subnet masks of 255.255.255.0 on the router interfaces.
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But routing protocols have not been configured.
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You can test your configuration by trying to log in to other routers on the internetwork.
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In some cases you will not succeed because there is no routing protocol enabled on the new router.
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The IP routing protocol only specifies the packet format for data.
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You need a protocol such as Router RIP to establish the connection.
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Using host names will have no effect either still as the router has no host translation table or DNS service to map the host names to the appropriate IP addresses.
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If you try entering a host name you will get an unreachable message.
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You can use Telnet with the relevant IP address to connect to other routers.
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Telnet verifies the application layer software between source and destination addresses.
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However, you will only be able to reach IP addresses on the subnets directly connected to the routers interfaces.
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For example, suppose you Telnet from router SanFran to Dublin Ethernet0 using Dublin's IP address 172.16.192.1.
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The router can make no contact with Ethernet0.
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As you can see here, the Ethernet port on Dublin is not a subnet directly connected to SanFran.
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And you can only log on to serial ports, because they are directly connected to the router.
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You can use the command ^RShow IP Route^r to examine the routing tables.
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The serial connections connect to Sydney and Dublin.
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The Ethernet connection mentioned is Ethernet0 interface on the SanFran router.
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The simplest testing method you can use is the Ping command.
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Ping uses the ICMP protocol to determine if protocol packets are being routed.
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The Ping user EXEC command can be used to diagnose basic network connectivity on AppleTalk, CLNS, IP, Novell IPX, Apollo, VINES, DECnet and XNS networks.
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The Ping command sends a datagram to the destination host and waits for a reply.
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The results can help evaluate path-to-host reliability.
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On the screen you can see five exclamation points, indicating that the destination address 172.16.67.2 responded successfully to all five Ping datagrams.
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If instead your display shows one or more periods (...), the application has timed out waiting for a datagram echo from the target.
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You can find out what path packets are taking to get to their destinations using the Trace command.
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This operation can be performed at the User or Privileged levels.
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The protocols that support Trace functions are IP, AppleTalk, VINES, and CLNS.
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The Trace command works by using the error messages generated by routers when a datagram exceeds its time-to-live (TTL) value.
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It starts by sending probe datagrams with a TTL value of one.
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This value causes the first router to discard the datagram and send back an error message.
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The Trace command sends several datagrams at each TTL level and displays the round trip time for each.
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When the router has a valid startup configuration stored in NVRAM, there are a few other settings, such as address resolution which you may need to configure.
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These settings can be entered in global Configuration mode.
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In Privileged mode, enter ^Rconfigure^r after the hash prompt to get into Configuration mode.
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Cisco IOS software uses three forms of address resolution:

• the Address Resolution
  Protocol(ARP) and proxy ARP
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• Probe (similar to ARP)
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• the Reverse Address
  Resolution Protocol (RARP)
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ARP is used to dynamically associate IP addresses with MAC or physical media addresses.
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And RARP requests IP addresses for MAC addresses.
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Probe is a protocol developed by Hewlett-Packard for use on IEEE-802.3 networks.
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When configuring address resolution you can perform the following tasks:

• define a static ARP Cache
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• set ARP encapsulations
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• disable proxy ARP
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<F>Most hosts support dynamic address resolution, so you do not usually need to specify static ARP cache entries.
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TCP/IP provides dynamic address resolution using the ARP and RARP protocols.
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Defining an ARP cache installs a permanent entry in the ARP cache, which associates an IP address with a media hardware address.
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Cisco IOS software uses this entry to translate 32-bit IP addresses into 48-bit hardware addresses.
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To display the type of ARP being used, and the timeout value, you can use the Show Interface command.
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If you want to examine the contents of the ARP cache, use the Show ARP command in User mode.
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To remove all non-static entries from the ARP cache you use the Clear ARP-Cache command in Privileged mode.
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Encapsulation controls the interface-specific handling of IP address resolution into 48-bit Ethernet hardware addresses.
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It is represented by the ARPA keyword.
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<F>Cisco IOS software can use the Probe protocol whenever it attempts to resolve an IEEE-802.3 or Ethernet local data-link address.
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Standard Ethernet-style ARP encapsulation is enabled by default on the IP interface.
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You can change this encapsulation method to SNAP or HP Probe as required by your network:

  arp{^Barpa^b|^Bprobe^b|^Bsnap^b}
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Cisco IOS uses proxy ARP to help hosts with no knowledge of routing determine the data-link address of hosts on other networks or subnets.
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For example, suppose a router receives an ARP request for a host that is not on the same network as the request sender.
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If the router has the best route to that host, it sends an ARP reply packet giving its own data-link or MAC address.
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The host that sent the ARP request then sends its packets to the router, which forwards them to the intended host.
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Proxy ARP is enabled by default.
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If you wish to disable proxy ARP you use the No IP Proxy ARP command.
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Proxy ARP is defined in RFC 1027.
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As you know, each IP address can have a host name associated with it.
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Cisco IOS software maintains a table of host names and associated IP addresses.
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This speeds up the process of converting names to addresses.
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Host names can be associated with one another through static or dynamic means.
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Host names are associated dynamically when DNS is available on the network.
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Manually assigning host names to addresses is useful when dynamic mapping is not available.
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To assign host names to IP addresses, you use the IP Host command in Configuration mode.
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The syntax for the command is

  ip ^Bhostname^b [^Btcp port^b
    ^Bnumber^b
    ^Baddress1^b[^Baddress2.. 
    address8^b]
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The name server holds a database of names mapped to IP addresses
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To map domain names you identify the host names, specify a name server, and enable the Domain Name System (DNS).
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You can specify a default domain name that Cisco IOS will use to complete domain name requests.
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You can specify a domain name or a list of domain names.
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Any IP host name that does not have a domain name will have the default domain you specify before being added to the host table.
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To specify a domain name or names, you use the following commands in Configuration mode:

  ip domain-name ^Bname^b
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  ip domain-list ^Bname^b
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You can have up to six hosts acting as name servers, supplying name information to the DNS.
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The syntax for specifying a name server is

  ip name server ^Bserver^b
    ^Baddress1^b[[^Bserver
    address2^b]..^Bserver^b-
    ^Baddress6^b]
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DNS is enabled by default.
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If you don't require a DNS service, you can disable it on the network using the No IP Domain-Lookup^R ^rcommand in Configuration mode.
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There are four routers on the network shown here.
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These are SanFran, London, Dublin, and Sydney.
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The routers communicate via WAN or serial cable connections.
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They direct data into Ethernet-based LANs.
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Each of the Ethernet and serial interfaces has an associated IP address.
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In this exercise you are going to use the router console terminal to discover preconfigured IP addresses and their subnet masks for routers on the network.
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First, you will examine the interfaces on the SanFran router.
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The Show Interface command displays the interfaces on the SanFran router.
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The first screen shows the BRI0 interface.
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It is not configured on any of the routers at this time.
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By pressing the ^Uspacebar^u you can display the next interface which is Ethernet0.
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Notice the IP address and subnet mask for this interface.
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The Serial0 interface comes up next.
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Notice its IP address and subnet mask.
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You can also see the Serial1 IP address.
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By pressing the ^Uspacebar^u again you will display the Serial1 interface on screen.
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You have now examined all the interfaces on the SanFran router.
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You can discover if there are other routers on the network.
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You can use the Show CDP Neighbors command to display information about other routers.
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The Show CDP Neighbors command gives information only about routers directly connected to the SanFran router.
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So the Dublin and Sydney routers are directly connected.
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For example, Sydney connects through the local Serial0 interface to SanFran.
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Dublin is connected to SanFran by the Serial1 interface.
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There are various ways of logging in to other routers.
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You can now connect to other routers simply by entering their host names (if they can be resolved in a host table or on DNS).
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Entering the host name implicitly invokes the Telnet program.
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Once you are connected to the remote host you are asked for a login password.
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You enter the login password ^Rcbtcbt^r, and the Dublin prompt appears.
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Now that you are logged on to the Dublin router, you can view its interface configuration.
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You can view the interface configuration on the Dublin router by using the Show Interface command.
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Note the Serial0 IP address and subnet mask.
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Notice the IP address and subnet mask on interface Serial1.
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You can discover the IP addresses and subnet masks on the Sydney router in exactly the same way.
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Now you can log out of the Dublin router.
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To log out of the Dublin router, you use the Exit command, and the SanFran# prompt returns to your screen.
