Configuring IP Addresses

You easily can configure a Cisco router to forward IP traffic when you understand IP addressing and the IOS configuration process described in Chapter 7, "Operating Cisco Routers." This chapter shows you examples of a variety of commands used to configure and troubleshoot the routing of IP packets in a Cisco router. Tables 13-2 and 13-3 summarize many of the most common commands used for IP configuration and verification.

You can refer to other sources for more information about basic IP configuration on Cisco routers. The Cisco IOS documentation is an excellent reference for additional IP commands (see Also, the Cisco Press book Interconnecting Cisco Network Devices is an excellent reference, particularly if you are not able to attend the instructor-led version of the class. This chapter focuses on the most common commands— the ones most likely to be on the CCNA exams.

Table 13-2 IP Configuration Commands


Configuration Mode

ip address ip-address mask [secondary]

Interface mode

ip host name [tcp-port-number] addressl [address2...address8]


ip route network-number network-mask {ip-address 1 interface} [distance] [name name]


ip name-server server-addressl [[server- address2]...server address6]


ip domain-lookup


ip routing


hostname name



Line configuration mode

password value

Line configuration mode

enable password [level level] {password 1 [encryption-type] encrypted-password}


enable secret [level level] {password 1 [encryption-type] encrypted-password}


keepalive [seconds]

Interface subcommand

exec-timeout minutes [seconds]

Line subcommand

logging synchronous

Line subcommand

Table 13-3 IP EXEC Commands



show hosts

Lists all host names and corresponding IP addresses

show interfaces [type number]

Lists interface statistics, including IP address

show ip interface [type number]

Provides a detailed view of IP parameter settings per interface

show ip interface brief

Provides a summary of all interfaces and their IP addresses

show ip route [ip-address [mask] [longer-prefixes]] 1 [protocol [process-id]]

Shows entire routing table or a subset if other parameters are entered

show ip arp [ip-address] [host-name] [mac-address] [type number]

Displays IP ARP cache

debug ip packet

Issues log messages for each IP packet

terminal ip netmask-format {bitcount | decimal | hexadecimal}

Sets type of display for subnet masks in show commands

ping [protocol 1 tag] {host-name 1 system-address}

Sends and receives ICMP echo messages to verify connectivity

trace [protocol] [destination]

Sends a series of UDP packets with increasing TTL values to verify the current route to a host

Most of the examples in this chapter refer to the routers in Figure 13-1. The figure shows a simple network with three routers, with each pair of routers having a serial link to the other two routers and a local Ethernet.

Figure 13-1 Sample Network with Three Routers, with Point-to-Point Serial Links



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