Transcript Semester 2 Chapter 10 - Institute of Technology Sligo

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Semester 2
Chapter 10
IP Addressing
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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
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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.
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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.
The routing table contains entries for network or wire addresses; it
usually contains no information about hosts.
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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.
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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.
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The number of routing bits (network and subnet bits) in each
subnet mask can also be indicated by the "/n " format.
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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
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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
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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 server
enable DNS.
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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-toaddress translation use
the no ip domainlookup 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.
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Show Hosts
Command
show host
Command
Description
Host
names of learned hosts
Flag
descriptions 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
the application
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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
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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
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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.
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!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.
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.
The END