Transcript Ch21 IP: Internet Addressing, Cisco Video

Department of Engineering Science
ES465/CES 440, Intro. to Networking & Network Management
IP: Internet Addressing
http://www.sonoma.edu/users/k/kujoory
References
• “Computer Networks & Internet,” Douglas Comer, 6th ed, Pearson, 2014, Ch 21,
Textbook, 5th ed, slides by Lami Kaya ([email protected]) with some changes.
• “Computer Networks,” A. Tanenbaum, 5th ed., Prentice Hall, 2011, ISBN:
13:978013212695-3.
• “Computer & Communication Networks,” Nader F. Mir, 2nd ed, Prentice Hall, 2015, ISBN:
13: 9780133814743.
• “Data Communications Networking,” Behrouz A. Forouzan, 4th ed, McGraw-Hill, 2007
• “Data & Computer Communications,” W. Stallings, 7th ed., Prentice Hall, 2004.
• “Computer Networks: A Systems Approach," L. Peterson, B. Davie, 4th Ed., Morgan
Kaufmann 2007.
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Topics Covered
• 21.1 Introduction
• 21.2 The Move to IPv6
• 21.3 The Hourglass Model &
Difficulty of Change
• 21.4 Addresses for the Virtual
Internet
• 21.5 The IP Addressing Scheme
• 21.6 The IP Address Hierarchy
• 21.7 Original Classes of IPv4
Addresses
• 21.8 IPv4 Dotted Decimal Notation
• 21.9 Authority for Addresses
• 21.10 IPv4 Subnet & Classless
Addressing
• 21.11 Address Masks
• 21.12 CIDR Notation Used With
IPv4
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21.13 A CIDR Example
21.14 CIDR Host Addresses
21.15 Special IPv4 Addresses
21.16 Summary of Special IPv4
Addresses
21.17 IPv4 Berkeley Broadcast
Address Form
21.18 Routers & the IPv4
Addressing Principle
21.19 Multi-Homed Hosts
21.20 IPv6 Multihoming & Network
Renumbering
21.21 IPv6 Addressing
21.22 IPv6 Colon Hexadecimal
Notation
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21.1 Introduction
• This chapter
– Explains the physical architecture of the Internet that
allows routers interconnect physical networks
– Begins a description of protocol software that makes
the Internet appear to be a single, seamless
communication system
– Introduces the addressing scheme used by IP version
4 (IPv4)
– Discusses the use of address masks for classless &
subnet addressing
– The Internet transition between IPv4 & IPv6
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2.2 The Move To IPv6
• Before we discuss IPv4 & IPv6
addressing, it is important to
– understand the change that is
occurring
– used a 32-bit address
• However, the global Internet
continues to grow exponentially
• IPv4 addressing has been
extremely successful to
accommodate
– The size doubling < a year
– all IPv4 has been assigned
– Heterogeneous networks
connect in the Internet
– Dramatic changes in hardware
technology
– Large scale across the world
• So why change?
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• IPv4 was designed to connect a
few computers originally &
• So, the primary motivation for
defining a new version of IP is
to allow
– much more address space to
accommodate the growth &
– Internet of Things
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21.3 The Hourglass Model & Difficulty of Change
• Although the scarcity of IP
addresses was apparent &
work on IPv6 began in 1993,
organizations were reluctant
to change to IPv6
• IPv4 with relatively insufficient
addressing capability lies in the
center of the Internet where
the hourglass is thin, although
– all applications use IP
– IP runs over different network
technologies
• So IP requires a change to
the entire Internet
Figure 21.1 The hourglass model of Internet
communication with IP at the center.
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21.4 Addresses for the Virtual Internet
• To achieve a seamless communication system
– protocol software must hide the details of physical networks
– it should offer the illusion of a single, large network
• From the point of view of an application
– the virtual Internet operates like any network
• allowing computers to send & receive packets
• The main difference between the Internet & a physical
network is
– Internet is an abstraction imagined by its designers & created
entirely by protocol software
• Thus, the designers chose
– addresses, packet formats, & delivery techniques independent of
the details of the underlying hardware
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21.4 Addresses for the Virtual Internet
• Addressing is a critical component of the Internet
• All host computers must use a uniform addressing
scheme
• Each address must be unique
• MAC (physical) addresses do not suffice because
– the Internet can include multiple network technologies, &
– each technology defines its own MAC addresses
• The advantage of IP addressing lies in uniformity:
– an arbitrary pair of application programs can communicate without
knowing the type of network hardware or MAC addresses being
used
• IP addresses are supplied by protocol software
– They are not part of the underlying network
• Many layers of protocol software use IP addresses
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21.5 The IPv4 Addressing Scheme
• Each host is assigned a unique 32-bit number
– known as the host's IP address (RFC 791, 2113) or Internet
address
• When sending a packet across the Internet, sender’s
protocol software must specify
– its own 32-bit IP address (source address) &
– the address of the intended recipient (destination address)
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21.6 The IP Address Hierarchy
• IP address is divided into two parts:
• A prefix, called Network address part or Net-ID
– identifies the physical network to which the host is attached
– Each network in the Internet is assigned a unique network ID
• A suffix, called Host address part or Host_ID
– identifies a specific computer (host/node) on the network
– Each computer on a given network is assigned a unique Host_ID
• IP address scheme guarantees two properties:
– Each computer is assigned a unique address, i.e.,
• a single address is never assigned to more than one computer
– Net_ID assignment must be coordinated globally &
Host_ID is assigned locally without global coordination
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21.7 Original Classes of IP Addresses
• How many bits to place in each part of an IP address?
– The Net_ID needs sufficient bits to allow a unique network # to
be assigned to each physical network in the Internet
– The Host_ID needs sufficient bits to permit each computer
attached to a network to be assigned a unique Host_ID
• No simple choice was possible to allocate bits!
– Choosing a large Net_ID accommodates many networks
• but limits the size of each network
– Choosing a large Host_ID means each physical network can
contain many computers
• but limits the total # of networks
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21.7 Original Classes of IP Addresses
• Internet contains a few large physical networks & many small
networks
– the designers chose an addressing scheme to accommodate a
combination of large & small networks
• The original classful IP addressing divides the IP address space
into 3 primary classes
– each class has a different size Net_ID & Host_ID
• The first 4 bits of an IP address determines the class to which the
address belongs
– They specify how the remainder of the address is divided into Net_IDs &
Host_IDs
• Fig. 21.1 illustrates the five address classes
– the leading bits identify each class, &
– the rest identify the Network address & Host address parts
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21.7 Original Classes of IPv4 Addresses
Net_ID = Prefix
Host_ID = Suffix
Replaces Figure 21.2 of Comer.
From IP address formats, Tanenbaum, computer networks, 5th ed, Fig 5-53.
Show:
- How many networks & how many host each network type allows?
- How can you identify each class by logical binary AND or OR operations?
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21.8 IPv4 Dotted Decimal Notation
• A notation more convenient for
humans to understand is used
• The accepted Notation is:
– Express each 8-bit section of a 32bit number as a decimal value
– Use periods to separate the sections
• The scheme is known as
dotted decimal notation
Figure 21.3 Examples of 32-bit binary #s & their
equivalent in dot-decimal notation used in IPv4
• Fig. 21.3 illustrates examples of binary numbers & the equivalent dotted
decimal notation
• Dotted decimal treats each octet (byte) as an unsigned binary integer
– the smallest value, 0
• occurs when all bits of an octet are zero (0)
– the largest value, 255
• occurs when all bits of an octet are one (1)
– dotted decimal addresses range
0.0.0.0 through 255.255.255.255
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21.9 Authority for Addresses
• Internet Corporation for Assigned Names & Numbers
(ICANN) authority has been established
– to handle address assignment & settle disputes
• ICANN does not assign individual Net_IDs
– Instead, ICANN authorizes a set of registrars to do so
• Registrars make blocks of addresses available to ISPs
– ISPs provide addresses to subscribers
• To obtain a Net_ID
– a corporation usually contacts an ISP
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21.10 IPv4 Subnet & Classless Addressing
• As the Internet grew
– the original classful
addressing scheme became
a limitation
• Everyone demanded a
class A or class B
address
– So they would have enough
addresses for future growth
• but many addresses in class
A & B were unused
– Many class C addresses
remained & few wanted to
use them
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• Two mechanisms were
invented to overcome the
limitation:
– Subnet addressing
– Classless addressing
• The two mechanisms are
closely related
– they can be considered to be
part of a single abstraction:
• instead of having three distinct
address classes, allow the
division between Net_ID &
Host_ID on an arbitrary bit
boundary
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21.10 IPv4 Subnet & Classless Addressing
• Subnet addressing was initially used within large
organizations – used also in IPv6
• Classless addressing extended the approach to all Internet
• They both facilitate using the IP addresses more effectively
since IP addresses are scarce
• Suppose an ISP that hands out Net_IDs & a small business
requests a Net_ID for a network that contains 35 hosts
– Classful addressing requires a complete class C with 8-bit Host_ID
– While 6 bits of Host_ID are needed to cover all possible host_IDs
• This means 28-35= 219 of the 254 possible Host_IDs would never be assigned
– So most of the class C address space is wasted
• For the above example
– classless addressing allows the ISP to assign
• a Net_ID that is 26 bits long
• a Host_ID that is 6 bits long
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21.10 IPv4 Subnet & Classless Addressing
• Assume an ISP owns a class C
Net_ID
• Classful addressing assigns the
entire Net_ID to one organization
• With classless addressing, the
– ISP can divide the Net_ID into several
longer Net_IDs, subnet &
– assign each to a subscriber
• Fig. 21.4 show classless addressing
Figure 21.4 (a) An IPv4 Class C prefix, &
(b) same prefix divided into 4 classless prefixes
• It allows ISP to divide a class C Net_ID into 4 longer Net_IDs
– each one can accommodate a network of up to 62 hosts
– the host portion of each Net_ID is shown in gray
• The original class C address uses 8 bits for Host_ID, while
– each of the classless addresses has 6 bits of Host_ID
• The classless Net_IDs will be unique as its original Class C
• Thus, instead of wasting addresses
– ISP can assign each of the 4 classless Net_IDs to a subscriber
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21.11 Address Masks
• How can an IP address be divided at an arbitrary
boundary & be recognizable by routers?
• Classless & subnet addressing schemes require hosts &
routers to specify & store an additional 32-bit addressing
information that
– specifies the exact boundary between Net_ID & Host_ID fields
– known as an address mask, also called a subnet mask
• The boundary size is represented as a bit-mask to make
the processing efficient
• Hosts & routers need to compare the Net_ID portion of
the address with the subnet mask in their forwarding
tables
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Address Mask
• In the 32-bit Mask in a classful address (below)
– N leftmost bits of Net_ID are 1s, &
– “32 – N” rightmost bits of Host_ID are 0s
N is fixed in Classful address
• In classless addressing, N can vary depending upon the desired # of bits
set for Net_ID field to design a cost effective subnet
• Thus, the Address Mask separates the network & host addresses to facilitate
the routing function in a router
• It identifies the block of addresses for devices on the same subnet, e.g.,
– Class C network addresses 199.199.5.0, 199.199.6.0, & 199.199.7.0 can be
combined by using a subnet mask of 255.255.252.0 for each
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Routing Using Subnets
To forward a packet, a
router identifies the subnet
by its address Mask
• IP network addresses that
are to be combined must
share the same high-order
bits
• By bitwise “AND”ing a
given IP address & its
Subnet Mask a router
can quickly identify which
subnet the address
belongs to & should
forward the packet to
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Default Class C mask
255.255.255.0
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21.12 CIDR Notation
• Classless Inter-Domain Routing
(CIDR, RFC 1817)
– CIDR only specifies addressing &
forwarding
– Designers wanted to make it easy for
a human to specify a mask
• Consider the mask needed for the
example in Fig. 21.4b
– It has 26 bits of 1s followed by 6 bits
of 0s
– In dotted decimal, the mask is:
255.255.255.192
192|10=1100,0000|2
Figure 21.4 (a) An IPv4 Class C prefix, &
(b) same prefix divided into 4 classless prefixes
• The general form of CIDR notation is: ddd.ddd.ddd.ddd/m
– ddd is the decimal value for an octet of the address
– m is the # of 1 bits in the mask
• Thus, one might write the following: 192.5.48.69/26
– which specifies a mask of 26 bits
• Fig. 21.5 lists address masks in CIDR notation
– along with the dotted decimal equivalent of each
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Fig. 21.5
A list of address
masks in CIDR
notation & in
dotted decimal
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21.13 A CIDR Example
• Assume an ISP has the following block 128.211.0.0/16
• Suppose the ISP has 2 customers
– one customer needs 12 IP addresses & the other needs 9
• The ISP can assign
– customer1 CIDR: 128.211.0.16/28
– customer2 CIDR: 128.211.0.32/28
– both customers have the same mask size (28 bits), the Net_IDs differ
• The binary value assigned to customer1 is:
10000000 11010011 00000000 0001 0000
• The binary value assigned to customer2 is:
10000000 11010011 00000000 0010 0000
• There is no ambiguity
– Each customer has a unique Net_ID
– More important, the ISP retains most of the original address block
• it can then allocate to other customers
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21.14 CIDR Host Addresses
• Once an ISP assigns a
customer a CIDR Net_ID
– the customer can assign host
addresses for its network users
• Suppose an organization is
assigned 128.211.0.16/28
• Fig. 21.6 illustrates that the
organization will have 4-bits to
use as a host address field
Figure 21.6 Illustration of IPv4 CIDR
addressing for an example /28 prefix.
– It shows the highest/lowest addresses in binary & dotted decimal
– The example avoids assigning the all 1s & all 0s host addresses
• Fig. 21.6 illustrates a disadvantage of classless addressing
• Because the host Host_ID can start on an arbitrary boundary
– values are not easy to read in dotted decimal, e.g.,
• when combined with the network Net_ID, the 14 possible host Host_IDs result in
dotted decimal values from 128.211.0.17 through 128.211.0.30
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21.15 Special IPv4 Addresses
• There are some special addresses that are reserved by
IP to denote networks or set of computers
– Special addresses are never assigned to hosts
• The syntax & semantics of each special address form
is explained in the following subsections
– 21.15.1 Network Address
– 21.15.2 Directed Broadcast Address
– 21.15.3 Limited Broadcast Address
– 21.15.4 This Computer Address
– 21.15.5 Loopback Address
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21.15.1 IPv4 Network Address
• One of the motivations for
defining special address forms
can be seen in Fig. 21.6
• It is convenient to have an
address that can be used to
denote the Net_ID assigned to
a given network
• IP reserves host address zero
– & uses it to denote a network
connecting a number of hosts
Figure 21.6 Illustration of IPv4 CIDR
addressing for an example /28 prefix.
• Thus, the address 128.211.0.16/28 denotes a network
– because the bits beyond the 28 are zero
• A network address should never appear as the destination
address in a packet
• Note: Section 21.17 discusses the Berkeley broadcast address form,
which is a nonstandard exception
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21.15.2 IPv4 Directed Broadcast Address
• To simplify broadcasting (send to all)
– IP defines a directed broadcast address for each physical network
• When a packet is sent to a network's directed broadcast
– a single copy of the packet travels across the Internet
• until it reaches the specified network
– the packet is then delivered to all hosts on the network
• The directed broadcast address for a network is formed by adding
a Host_ID that consists of all 1 bits to the network Net_ID
How does broadcast work?
• If network hardware supports broadcast
– a directed broadcast will be delivered using the hardware broadcast
capability
• If a particular network does not have hardware support for broadcast
– software must send a separate copy of the packet to each host on the
network
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21.15.3 IPv4 Limited Broadcast Address
• Limited broadcast refers to a broadcast on a directlyconnected network
– informally, we say that the broadcast is limited to a “single wire”
• Limited broadcast is used during system startup
– by a computer that does not yet know the network number
• IP reserves the address consisting of 32-bits of 1s
– refer to limited broadcast
• Thus, IP will broadcasts any packet sent to the all-1s
address across the local network
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21.15.4 IPv4 This Computer Address
• A computer needs to know its IP address
– before it can send or receive Internet packets
• TCP/IP contains protocols a computer can use to obtain
its IP address automatically when the computer boots
– The startup protocols also use an IP to communicate
• When using such startup protocols
– a computer cannot supply a correct IP source address
– To handle such cases
• IP reserves the address that consists of all 0s to mean this computer
Find out:
- How do you identify your computer IP address?
- What is your computer address whether Windows or Mac PC?
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21.15.5 IPv4 Loopback Address
• Loopback address used to test network applications
• It is used for preliminary debugging after a network
application has been created
• A programmer must have two application programs that
are intended to communicate across a network
– Each application includes the code needed to interact with TCP/IP
• Instead of executing each program on a separate
computer
– the programmer runs both programs on a single computer, &
– instructs them to use a loopback address when communicating
• When one application sends data to another
– data travels down the protocol stack to the IP software, then
– forwards it back up through the protocol stack to the second
program
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21.15.5 IPv4 Loopback Address
• A programmer can test the program logic quickly
– without needing two computers & without sending packets across
a network
• IP reserves the network Net_ID 127/8 for use with
loopback
• The host address used with 127 is irrelevant
– all host addresses are treated the same
– programmers often use host # 1
– so it makes 127.0.0.1 the most popular loopback address
• During loopback testing no packets ever leaves a
computer
– the IP software forwards packets from one application to another
• The loopback address never appears in a packet
traveling across a network
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21.16 Summary of Special IPv4 Addresses
• Figure 21.7 lists a set of special address forms
reserved by IP
– Special addresses are never assigned to hosts
Figure 21.7 Summary of the special IP address forms.
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21.17 IPv4 Berkeley Broadcast Address Form
• The UC Berkeley developed & distributed an early implementation of
TCP/IP protocols
– known as Berkeley Software Distribution as part of UNIX (BSD UNIX)
• BSD implementation contained a nonstandard feature
– Berkeley implementation uses a host Host_ID that contains all 0s instead
of all 1s to represent directed broadcast
– this address form is known as Berkeley broadcast
• Initially many computer manufacturers derived their early TCP/IP
software from the Berkeley implementation, &
– a few sites still use Berkeley broadcast
• TCP/IP implementations often include a configuration parameter
– that can select between the TCP/IP standard & the Berkeley form
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21.18 Routers & IP Addressing Principle
• Each router is assigned two or more IP addresses
– one address for each network to which the router attaches
• A single IP address does not suffice for a router
– because each router connects to multiple networks, &
– each network has a unique Net_ID
• The IP scheme can be explained by a principle:
– An IP address does not identify a specific computer
– Each address identifies a connection between a computer & a
network
– A computer with multiple network connections (e.g., a router)
must be assigned one IP address for each connection
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21.18 Routers & the IP Addressing Principle
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21.19 Multi-Homed Hosts
• Can a host connect to multiple networks? Yes
• A host computer with multiple network connections is
said to be multi-homed
• Multi-homing is sometimes used to increase reliability
– if one network fails, the host can still reach the Internet through the
second connection
• Alternatively, multi-homing is used to increase
performance
– connections to multiple networks can make it possible to send
traffic directly & avoid routers, which are sometimes congested
• Like a router, a multi-homed host has multiple protocol
addresses
– one for each network connection
• The computers in Salazar 2006 have three Ethernet ports
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21.20 IPv6 Multihoming & Network Renumbering
• IPv6 promotes multihoming to
a central position, though IPv4
prohibits it
• IPv6 host assumes to have
multiple connections & multiple
addresses
– Motivation for a network to have
multiple prefixes (Net_IDs)
comes from need to renumber
networks
• When an organization
changes its service provider,
IPV6 makes it easier
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• Protocols were designed so the
new prefix could be added
while running applications
continued to use the old prefix
– When an application was
launched, the application would
use the new prefix &
• soon all applications would be
using the new prefix &
• the old prefix could be
removed
• It is sad that after years of work
on network renumbering in
IPv6, automated renumbering is
not still practical
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21.21 IPv6 Addressing
• IPv4 & IPv6 (RFC 1365, 2590) assign address for each computer
connection & a physical network
– A router needs at least 3 IPv6 addresses to connect to 3 physical
networks
– IPv6 permits multiple prefixes (Net_IDs) to be assigned to a given network
• IPv6 uses 128 bits & includes 3 levels of addressing hierarchy
– Global prefix for routing in the Internet (variable size)
– Subnet for subnets at the organization (variable size)
– Interface for a specific computer (64 bits)
Figure 21.9 The division of a 128-bit IPv6 address into Net_ID, subnet, & interface sections.
The interface is 64 bit wide.
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21.21 IPv6 Addressing
• IPv6 defines three types of addresses
Figure 21.10 The three types of IPv6 addresses.
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21.21 IPv6 Addressing
• Anycast addressing was originally known as cluster
addressing
– The motivation for such addressing arises from a desire to allow
replication of services, e.g.,
• A corporation that offers a service over the network assigns an anycast
address to several computers/servers that provide the service
• When a user sends a datagram to the anycast address, IPv6 routes
the datagram to one of the computers in the set (i.e., in the cluster)
• If a user from another location sends a datagram to the
anycast address
– IPv6 can choose to route the datagram to a different member of
the set
– allowing both computers to process requests at the same time
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21.22 IPv6 Colon Hexadecimal Notation
• IPv6 address occupies 128 bits
– writing such #s can be unwieldy & difficult to handle
• Consider a 128-bit number in the dotted decimal notation:
105.220.136.100.255.255.255.255.0.0.18.128.140.10.255.255
• To reduce the # of characters used to write addresses
– designers of IPv6 chose a more compact syntactic form known as
colon hexadecimal notation, usually abbreviated colon hex
– each group of 16 bits is written in hex with a colon separating
groups
• When the above # is written in colon hex:
69DC : 8864 : FFFF : FFFF : 0 : 1280 : 8C0A : FFFF
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21.22 IPv6 Colon Hexadecimal Notation
• An additional optimization known as zero compression
further reduces the size
– Zero compression replaces sequences of zeroes with two colons
– E.g., the address:
FF0C:0:0:0:0:0:0:B1  FF0C : : B1
• The large IPv6 address spaces make zero compression
especially important
– designers expect many IPv6 addresses to contain strings of zeroes
• To help ease the transition to the new protocol
– designers mapped existing IPv4 addresses into the IPv6 address
space
– Any IPv6 address that begins with 96-zero bits contains an IPv4
address in the low-order 32-bits
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