Transcript Unit Overview PowerPoint

Network Addressing
Networking for Home and Small Businesses – Chapter 5
Darren Shaver – Modified Fall 2007
© 2007 Cisco Systems, Inc. All rights reserved.
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Objectives
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Describe the purpose of an IP address and Subnet
Mask and how they are used on the Internet.
Describe the types of IP Addresses available.
Describe the methods of obtaining an IP Address.
Describe the use of NAT on a home or small business
network using an Integrated Router.
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IP Address and Subnet Mask
 A logical address unique to a particular device
 IP Addresses assigned to host & end-user devices
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Structure of an IP Address
 32 Bits divided into 4 8-bit sections called octets by periods
 Addresses are assigned using decimal, not binary numbers
 IP version 4
– Most common used
– 4 trillion (4,294,967,296) possible addresses (232)
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Purpose of an IP Address and Subnet Mask
 IP Addressing is logical and heirarchical
 Example Address 192.168.100.39 (Class C)
– First section 192.168.100 is network portion
– Second section 39 is host portion
 Routers only need network address, not each host
 Less info in tables, faster routing
 Telephone system is also heirarchical, with country, area, and
exchange codes.
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Subnet Mask
 Every IP address has two parts,
network and host
 How does the host, router, or other
device know which?
 Subnet mask
– Also 32-bit number
– Compared with IP address bit to bit
(ANDing)
– 1s are network bits, 0s are host bits
 Hosts compare address to its own
before sending
– Same mask - Local addresses
have and sent locally
– Different mask - Network
addresses are sent to router
 Number of Hosts by Bits
– If there are 8 host bits, there are 28
hosts possible, or 256 (0-255)
– 16 bits - 216, or 65,536
– 24 bits - 224, or 16,777,216
 IP address that have all zeros in the
host portion are network or
subnetwork addresses, not
available for hosts assignment
 IP addresses with all 1s in the host
portion are broadcast addresses,
also not assigned
 Most common masks:
– 255.0.0.0
– 255.255.0.0
– 255.255.255.0
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8 bit
16 bit
24 Bit
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Network ANDing Compare
AND Logic
 1 and 1 = 1
 1 and 0 = 0
 0 and 1 = 0
 0 and 0 = 0
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Classes of IP Addresses
 5 Classes of IP address Default subnet masks
Network
Size/
Purpose
 Large
 Medium
 Small
 Multicast
 Experim
ental
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Private Addressing
 Public addresses are unique out on the Internet
 Risk of using up all unique addresses
 RFC 1918 - Private Addressing
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Can be used within private network without going on Internet
Class A - Very Large - Over 16 million
Class B - Medium, about 65,000
Class C - Small, only 256 addresses, or 254 hosts
Unique class, 127.0.0.0 used for loopback addresses
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Types of IP Packets and Frames
 Unicast
– Most common
– One destination
 Broadcast
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Contains all 1s in the host portion
All local hosts will receive and read packet
Used by ARP and DHCP
Example: 192.168.35.0 255.255.255.0 broadcast address is
192.168.35.255
– Broadcast IP needs broadcast MAC address in Ethernet frame FF:FF:FF:FF:FF:FF (48 bits of 1)
 Multicast
– One source, many destinations
– Address range is 224.0.0.0 to 239.255.255.255
– Multicast IP needs matching Ethernet frame address
• Always begins with 01-00-5E
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Unicast Frame
 The IP packet has been encapsulated by the Framing
information.
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Broadcast Frame
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Multicast Frame
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Obtaining an IP Address
 Methods of assigning an IP Address
– Static
• Configured by host administrator
• Used for servers, printers, and other
devices shared by users
• Time consuming
• List must be maintained
• Can introduce errors
– Dynamic
• Good where assignments change
often
• DHCP (Dynamic Host Control
Protocol) used
• Assigns other default information
– Subnet mask
– Default gateway
– DNS server, etc.
• Leased for period of time and
returned to pool when not in use
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DHCP Servers
 Locations and methods of connection vary based on which
network you’re associating with.
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DHCP Configuration on ISR
 Newly configured hosts have no IP address, subnet mask, or gateway
 Needs to get this from a DHCP Server
 DHCP Process to get settings information:
– DHCP DISCOVER Packet
• Broadcast
– IP: 255.255.255.255
– MAC: FF:FF:FF:FF:FF:FF)
– DHCP server Replies with OFFER containing suggested IP address
– Host sends REQUEST asking to use IP Address
– Server replies with ACKNOWLEDGEMENT
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DHCP Configuration
 SOHO Networks usually use
an ISR for DHCP
 The basic DHCP Settings:
– Default network address for
gateway on an ISR is normally a
private Class C (192.168.1.1,
192.168.100.1)
– A pool of addresses
– Lease time for address
– Maximum number of hosts
• Can you exceed 20?
 Every host must have this Gateway
address configured
– Either statically or dynamically
– What does this mean? Describe
process…
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Network Boundaries and Gateways
 Routers for local networks provide gateway for communication
to other networks
 Each Interface on router is a separate network connection
 IP Addresses on interfaces identify networks connected
 ISP Side of the router
– ISPs use DHCP to give addresses to SOHO routers connecting to their
network
– ISRs act as a DHCP client when connecting to ISP
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Internet Connection Methods
 Direct Connection
– Single computer connected through a modem
– ISP is assigned directly through modem to a single host
 Connection through ISR – with Modem (WAN Device)
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Many computers connected to ISR
ISR connected to ISP using connection through modem
ISP assigns address to ISR interface connected to modem
Hosts assigned addresses from ISR
 Connection through Gateway Device – no Modem
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–
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Many computers connected to ISR
ISR connected to ISP with integrated modem port
ISP assigns address to ISR interface connected to modem
Hosts assigned addresses from ISR
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Internet Connection Methods
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Using NAT with a Home or Small Business Network
 ISP provides public address for ISR to use externally
 ISR provides private addresses used on internal network
 NAT (Network Address Translation) is used to bridge the gap
and match the public and private addresses.
 Packets sent to the Internet have their IP addresses stripped
away and another, external address assigned.
 Reverse process is applied with incoming traffic.
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Summary
 IP addresses are unique 32-bit addresses grouped into four 8-bit
bytes called octets.
 IP addresses use a two-part hierarchical structure of network
bits and host bits.
 IP addresses and subnet masks are used by routers to
determine the network location of hosts.
 IP addresses are grouped into classes according to the number
of bits used for designating the network, and further divided into
public and private ranges.
 Private IP addresses must be translated to public IP addresses
in order to move through the Internet.
 IP addresses can be assigned statically or dynamically.
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