Semester 2v2Chapter 10:  IP Addressing

10.1.1.1.    Describe how IP addressing is important in routing.

IP addresses are specified in 32-bit dotted-decimal format.

Router interfaces must be configured with an IP address if IP is to be routed to or from the interface.

ping and trace commands can be used to verify IP address configuration

Each company or organization listed on the Internet is seen as a single unique network that must be reached before an individual host within that company can be contacted.

Each company network has an address; the hosts that live on that network share that same network address, but each host is identified by the unique host

address on the network.

The routing table contains entries for network or wire addresses; it usually contains no information about hosts.

Each device or interface must have a host number that does not have all 0s in the host field.

A host address of all 1s is reserved for an IP broadcast

into that network.

A host value of 0 means "this network" or "the wire itself" (e.g. 172.16.0.0). A value of 0 is also used, though rarely, for IP broadcasts in some early

TCP/IP implementations.

An IP address and a subnet mask on an interface achieve three purposes:

•They enable the system to process the receipt and transmission of packets.

•They specify the device’s local address.

•They specify a range of addresses that share the cable with the device.

Broadcasting messages are intended to be seen by every host on a network.

The broadcast address is formed by using all 1s within a portion of the IP address

Two kinds of broadcasts - directed broadcasts  and

flooded broadcasts.

Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directed broadcasts contain all 1s in the host portion of the address.

Flooded broadcasts (255.255.255.255) are not propagated, but are considered local broadcasts.

The number of routing bits (network and subnet bits) in each subnet mask can also be indicated by the "/n " format.

Use the term ip netmask-format command to specify the format of network masks for the current session. Format options are:

•bit count

•dotted-decimal (default)

•hexadecimal

The ip host command makes a static name-to-address entry in the router’s configuration file.

Example : IP host WORK 174.17.1. 101

The ip name-server command defines which hosts can provide the name service. You can specify a  maximum of six IP addresses as name servers in a single command.

To map domain names to IP addresses, you must identify the

host names specify a name serverenable DNS.

Cisco IOS software maintains a cache of host name-to-address mappings for use by EXEC commands.

This cache speeds the process of converting names to addresses.

To turn off the name-to-address translation use the no ip domain-

lookup command.

A name such as ftp.cisco.com identifies the domain of the File Transfer Protocol (FTP) for Cisco. To keep track of domain names, IP identifies a name server that manages the name cache.

show host Command

Description

Host names of learned hosts

Flagdescriptions of how information was learned and its current status

perm manually configured in a static host table

temp acquired from DNS use

OK entry is current

EX entry has aged-out,  expired

Age time measured in hours since software referred to the entry

Type protocol field

Address(es) logical addresses associated with the host name

Show Hosts Command

•telnet -verifies the application layer software between source and destination stations; is the most complete testing mechanism available

•ping - uses the ICMP protocol to verify the hardware connection and the logical address at the network layer; is a very basic testing mechanism

•trace - uses TTL values to generate messages from each router used along the path; is very powerful in its ability to locate failures in the path from the source to the destination

Character Definition

! successful receipt of an echo reply

. timed out waiting for datagram reply

U destination unreachable error

C congestion-experienced packet

I ping interrupted (e.g. Ctrl-Shift-6 X)

? packet type unknown

& packet TTL exceeded

The extended ping command is supported only from privileged EXEC mode.

You can use the extended command mode of the ping command to specify the supported Internet header options.

To enter the extended mode, enter ping <return>, then Y at the extended commands prompt.

Host names are shown if the addresses are translated dynamically or via static host table entries. The times listed represent the time required for each of three probes to return.

NOTE: trace is supported by IP, CLNS, VINES, and AppleTalk. When the trace reaches the target destination, an asterisk (*) is reported at the display. This is normally caused by a time out in response to one of the probe packets.

!H - The probe was received by the router, but not forwarded, usually due to an access list.

P - The protocol was unreachable.

N - The network was unreachable.

U - The port was unreachable.

* - Time out.

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