Transcript PPT

Addressing in TCP/IP
LESSON 6
(September 22, 1995)
Daniel Z. Tabor Jr.
New Jersey Institute of Technology
Lesson 6 - (1 of 37)
Outline:
Addressing in TCP/IP
• A Need for Identification
• Internet Address
Classification
• Network and Host ID
Ranges
• Addresses Specify Network
Connections
• Network and Broadcast
Addresses
• Multicast Addresses
• Weaknesses in IP
Addresses
• Common Representation
of Addresses
• Loopback Addresses
• Obtaining an IP Address
• Contacting the NIC
• Network Byte Ordering
• Mapping Names to IP
Addresses
Lesson 6 - (2 of 37)
A Need for Identification:
• There is a need to establish:
– A globally accepted method of identifying
computers.
– To provide a universal communication service.
Lesson 6 - (3 of 37)
A Need for Identification:
• TCP/IP universal host identifiers - are standard
compact binary addresses used for efficient
computation in routing and identification.
– Scheme is analogous to physical network
addressing where:
• Each host on the internet is assigned an integer
address (IP address) of 32-bits.
• That address is represented in “dotted-decimal”
notation.
Lesson 6 - (4 of 37)
A Need for Identification:
– Each address is a conceptual pair of
(netid, hostid)
• netid:
identifies a network
• hostid:
identifies a host on that network.
Lesson 6 - (5 of 37)
Internet Address Classification:
• IP Addresses (version 4)
– Five classes (A,B,C,D,E)
– They are distinguished by their first 5 bits.
– Addresses are 32-bits.
• Later versions of the Internet Protocol may have
more classes and use a different number of bits to
represent an address.
– IPv6 (proposed) uses 64-bits.
Lesson 6 - (6 of 37)
Internet Address Classification:
• Class E - (11110) - Reserved for future use.
• Class D - (1110) - Multicast addressing.
– Currently being used with applications that use
selective broadcasting in communication:
• Video-conferencing.
• MBONE
• Audio-conferencing.
Lesson 6 - (7 of 37)
Internet Address Classification:
• The three highest-order bits are used to determine
the three Primary Classes:
• Class A - (0) - used for a handful of networks
which have more than 65,536 (216) hosts attached
to each.
– Netid = 7 bits
– Hostid = 24 bits
– Ex. (10.0.0.1) - ARPANET
Lesson 6 - (8 of 37)
Internet Address Classification:
• Class B - (10) - used for intermediate size
networks that have between 256 (28) and 65,536
(216) hosts attached to each.
– Netid = 14 bits
– Hostid = 16 bits
– Ex. (128.235.251.11) - Hertz.njit.edu
Lesson 6 - (9 of 37)
Internet Address Classification:
• Class C - (110) smallest configuration for hosts.
Allows for less than 256 (28) hosts attached to
each.
– Netid = 21 bits
– Hostid = 8 bits
– Ex. (195.213.49.3) - Local area networks
• Addresses are designed to allow extraction of
either id quickly which makes gateway routing
more efficient.
Lesson 6 - (10 of 37)
IPv4 Address Types:
Class A
0 1 2 3 4
netid
0
Class B
1 0
Class C
1 1 0
Class D
1 1 1 0
Class E
1 1 1 0
8
16
24
31
hostid
netid
hostid
netid
hostid
multicast address
reserved for future use
1
Lesson 6 - (11 of 37)
Network and Host ID
Ranges:
Address
Class A
Class B
Class C
Class D
Network Range
Host Range
0.0.0.0 - 127.0.0.0
0.0.0 - 255.255.255
128.0.0.0 - 191.255.0.0
0.0 - 255.255
192.0.0.0 - 223.255.255.0
0 - 255
224.0.0.0 - 239.255.255.255
N/A
Lesson 6 - (12 of 37)
Addresses Specify Network
Connections:
• Gateways connect two or more physical networks.
Each connection requires its own IP address.
• Conventional computers that have two or more
physical connections are called multi-homed hosts
and require multiple IP addresses.
• IP addresses specify both a network and a host on
that network (not an individual machine, but its
connection to the network).
Lesson 6 - (13 of 37)
Network and Broadcast
Addresses:
• Hostid = 0 (128.235.0.0) : names/addresses the
network as a whole. (Ex. NJIT network)
• Hostid = All 1’s (128.235.255.255) : directed
broadcast address which refers to every host on
that network. (Ex. Hertz.njit.edu)
• Netid & Hostid = All 1’s (255.255.255.255) :
limited broadcast address provides broadcast
address independent of assigned Netid.
Lesson 6 - (14 of 37)
Network and Broadcast
Addresses:
• Directed broadcast addresses require knowledge
of the network address, limited broadcast
addresses do not.
• Limited broadcast addresses provide a broadcast
address for local networks, independent of the
assigned Netid.
Lesson 6 - (15 of 37)
Network and Broadcast
Addresses: Notations
• 1’s => ‘All’
• 0’s => ‘This’
• Netid = 0 => ‘This network’
Lesson 6 - (16 of 37)
Multicast Addresses:
• Multicast addresses - provide multi-point delivery
of packets.
• Also known as selective broadcasting, multicast
addressing is a subset of normal broadcasting.
• Multicast addresses can be hardware or software
addresses.
• See Lesson 17 (Multicast IP and the MBONE) for
further information.
Lesson 6 - (17 of 37)
Weaknesses in IP Addresses:
• If a host moves to a different network, it must
change it’s IP address.
• If the number of hosts grows more than
255 (Class C):
– The addressing scheme must be changed to a
Class B.
– Extremely time consuming administration
changes must also be made to enable the
address change.
Lesson 6 - (18 of 37)
Weaknesses in IP Addresses:
• Routing:
– Multiple IP addresses for a single host may be
routed entirely different from each other.
– The route chosen depends upon the address
chosen (in some cases).
– Knowing only one IP address for a single host
may sometimes NOT be enough.
Lesson 6 - (19 of 37)
Weaknesses in IP Addresses:
• Availability:
– The number of available IP addresses is rapidly
reducing, forcing temporary extensions of the
IP addressing scheme, until a more scaleable
scheme can be put in place.
– If a stable replacement for the current IP
addressing scheme is not in place within 5-10
years, all IP addresses will be completely
exhausted. (IPv6)
Lesson 6 - (20 of 37)
Common Representation
of Addresses:
• Dotted Decimal Notation - a common way of
representing an IP address by using four decimal
integers separated by decimal points to ease in
reading.
• Each integer represents the value of the binary
numbers contained within that octet of the address.
• Example:
10000000 00001010 00000010 00011110 =
128.10.2.30
Lesson 6 - (21 of 37)
Loopback Addresses:
• Class A address 127.0.0.0
– Reserved for loopback on any local machine to
test the communication system and for interprocess communication (IPC) on that machine.
– Network 127 addresses should never appear on
any network, be routed or propagated beyond
the network interface card (NIC).
– Commonly used as local IP addresses when
configuring PCs for pseudo-SLIP connectivity.
Lesson 6 - (22 of 37)
Summary of Addresses:
all 0s
all 0s
This host
host
all 1s
net
127
Host on this net
Limited broadcast
(local net)
all 1s
anything (often 1)
Directed broadcast
for net
Loopback
Lesson 6 - (23 of 37)
Obtaining an IP Address:
• Network Information Center (NIC) is the central
authority which ensures that all Internet addresses
are unique. It does so by managing the approval
and assignment of all IP network addresses.
• When requesting an IP address, you should choose
a type which fits the current and anticipated future
sizes of your company.
Lesson 6 - (24 of 37)
Obtaining an IP Address:
• Sample size networks and appropriate address
classes:
– Local Area Networks:
Class C
– Campus-wide Networks: Class B
– Large Companies:
Class B
– International Networks: Class A
Lesson 6 - (25 of 37)
Image source: Internetworking with TCP/IP vol I
(1995 Prentice Hall, Douglas Comer)
Lesson 6 - (26 of 37)
Obtaining an IP Address:
• Applying for IP addresses is only needed if your
network is going to be connected to the Internet on
a permanent basis.
• Currently there is a long waiting list for companies
and organizations to obtain IP addresses.
• The NIC may soon charge for IP addresses
because of the increased demand and lack of
available addresses.
Lesson 6 - (27 of 37)
Obtaining an IP Address:
• When should an organization apply for an IP
address?
– Any organization that connects to the Internet
has no option, they must obtain a registered
number.
– If an organization communicates with it’s
subsidiaries using the Internet, it too must
request a registered number.
Lesson 6 - (28 of 37)
Obtaining an IP Address:
• Advantages and Disadvantages of Registering:
– Advantage:
• Ensuring that your address and naming conventions
are protected (njit.edu).
– Disadvantage:
• When you connect to the Internet, your use of a
registered address is recorded in the Assigned
Numbers RFC along with a contact names of
administrators and policy personnel..
Lesson 6 - (29 of 37)
Obtaining an IP Address:
• Choosing a network number without official
registration:
– Avoid Class A addresses.
– Do not copy examples given in a configuration
handbook or textbook.
– Avoid well-known addresses that are published.
– Use high-end Class B or C addresses at
random.
Lesson 6 - (30 of 37)
Contacting the Network
Information Center:
• Contacting the NIC:
– Snail Mail:
Government Systems Inc,
Attn: Network Information Center
14200 Park Meadow Drive
Suite 200
Chantilly, VA 22021
Lesson 6 - (31 of 37)
Contacting the Network
Information Center (continued):
– Voice:
• 1-703-802-4535
• 1-800-365-DNIC
– Fax:
• 1-703-802-8376
– E-Mail:
• [email protected]
Lesson 6 - (32 of 37)
Network Byte Ordering:
• Little Endian - lowest memory address contains
low-order byte of integer.
• Big Endian - lowest memory address holds the
high-order byte of the integer.
• Direct copying may change the value of data from
machine to machine.
• TCP/IP protocols define Network Standard Byte
Order - most signification byte first (Big Endian)
Lesson 6 - (33 of 37)
Mapping Names to
IP Addresses:
• Most users do not directly use IP addresses when
using network services, they use Domain Names
which map to IP addresses.
• When connecting to a server at NJIT, you use the
domain name (hertz.njit.edu) and not it’s IP
address (128.235.251.11).
• Domain names are not IP addresses, but mapped
to them for readability by the Domain Naming
System (Lesson 13).
Lesson 6 - (34 of 37)
ETHERNET 128.10.0.0
128.10.2.3
128.10.2.8
MERLIN
GUENEVERE
(multi-homed
(Ethernet
host)
host)
192.5.48.3
GLATISANT
(router)
192.4.48.7
128.10.2.70
TOKEN
RING
192.5.48.0
128.10.2.26
LANCELOT
(Ethernet
host)
TALIESYN
(router)
192.5.48.6
10.0.0.37
192.5.48.1
ARTHUR (token ring host)
To ARPANET
Image source:
Internetworking with
TCP/IP vol I
(1995 Prentice Hall,
Douglas Comer)
Lesson 6 - (35 of 37)
Questions
Addressing in TCP/IP
• What range of addresses should never appear on a
network?
• If billions of different IP addresses can be created
from 32-bits, why is there a shortage?
• If we can identify computers using hardware
addresses, why use IP addresses?
• What are the differences between the IP
addressing scheme and the U.S. telephone
numbering scheme?
Lesson 6 - (36 of 37)
• Why have a network standard byte order?
Reference Materials
Addressing in TCP/IP
• IP Address to Latitude/Longitude (http://cello.cs.uiuc.edu/cgi-bin/slamm/ip2ll/)
• Network Information Center (NIC) (http://ds.internic.net/)
• DNS Resources Directory (http://www.dns.net/dnsrd/)
• Internetworking w/ TCP/IP Vol I, Douglas Comer.
• Internet Standards - RFCs
(ftp://nic.merit.edu/documents/std/)
Lesson 6 - (37 of 37)