Transcript netLyr-address

Network Layer
• We have discussed data link architectures
 CSMA/CD
 Point-to-Point
 Wireless LANs
• These architectures deliver frames to next
station
• They implement network segments, possibly
connected through bridges
• One might build a private medium size private
network this way
• Could not build a universal or public network this
way
Network Layer
• We would like to interconnect such
networks into a consistent larger network
• We could consider this larger network an
internet, an interconnection of networks
• Logical ‘gluing’ of heterogeneous layer 2
networks to appear as a single network
• A number of issues must be addressed
 Universal addressing
 Routing
 Packetizing data
Network Layer
Network Layer
Addressing
CSMA/CD
IEEE802.3
Routing
IEEE 802.11
Physical Layer
Twisted pairs
Fiber Optics
encoding
Packetizing
Pt-to-Pt
HDLC
PPP
Network Layer
• There are and have been many network layer
protocols
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Systems Network Architecture (SNA) – IBM
DECNET – Digital Equipment Corporation
OSI – International Standards Organization
AppleTalk – Apple Computer
Internetwork Packet Exchange (IPX) – Novell
Internet Protocol (IP)
• Each of these has its own addressing scheme
• Each has own packet format
• Each implements own versions of routing
Network Layer
• We will discuss the Internet Protocol
• Recall, this is layered protocol, much like
the OSI model
• Internet Protocol does not have its own
physical or data link layers
• Uses existing lower layer protocols as
discussed
• The Internet Protocol is often called
TCP/IP which represents its two
underlying protocols
Comparison of OSI and TCP/IP
Data Link
Physical
Internet Protocol Historical Summary
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1969 – Four node ARPANET established
1973 – Development of TCP/IP suite begins
1978 – UNIX distributed to academic sites
1981 – CSNET established
1983 – TCP/IP becomes official protocol
1983 – NSF funds a national backbone linking 6
supercomputer centers
 Emerging regional networks link to backbone nodes
 Initial backbone 56Kbps
Internet Protocol Historical Summary
• 1987 – NSF backbone increased to T1
 Partnership formed to operate NSFnet
• Merit – Michigan
• IBM
• MCI
• 1991 NSFNET backbone increased to 45 Mbps
• 1993 – NSFNET establishes migration to a
commercial Internet
• 1995 – Internet Service Providers (ISPs)
established
Internet 2
• Established in 1998
• Separate physical network for research
institutions
• Uses same Internet Protocol
• Network Operations Center (noc) at Indiana
University
• Core Network called Abilene
• Circuits provided by Qwest Communications
Abilene Access Nodes
Seattle
Cleveland
Sacramento
New York
Denver
Indianapolis
Kansas City
Los Angeles
Atlanta
Abilene Core Node
Abilene Access Node
Operational January 1999
Houston
Internet today
Internet Standards Bodies
Internet Society (ISOC)
http://www.isoc.org
Internet Architecture Board (IAB)
http://www.iab.org
Internet Research Task Force
(IRTF)
http://www.irtf.org
Internet Engineering Task Force
(IETF)
http://www.ietf.org
Internet Protocols
Routing
Management
Internet Standards Documentation
• Official standards published in documents called
Request for Comments (RFCs)
• RFCs go through various stages
 Internet Draft
• Experimental
• Informational
• Proposed standard
– Draft Standard
– Internet Standard
• RFCs are stored in a public repository
http://www.ietf.org
Internet Addressing
• For an Internet, we need universal
identification of nodes
• Must apply to different types of networks
• Must be independent of vendor, hardware,
physical network
• In TCP/IP we deal with various addresses
 Physical addresses – MAC addresses
 IP addresses – universal address
 Port – specifies service
Internet Addressing
• Administration of Internet addresses
 Internet Corporation for Assigned Names and
Numbers (ICANN)
http://www.icann.org
 Internet Assigned Numbers Authority (IANA)
http://www.iana.org
Authorizes and oversees 5 registries
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APNIC (Asia Pacific Network Information Centre)
ARIN (American Registry for Internet Numbers)
RIPE NCC (Réseaux IP Européens)
LACNIC (Regional Latin-American and Caribbean IP Address
Registry)
• AfriNIC (African Network Information Centre)
Internet Address
• An IP address is 32 bit word
• Maximum of 232 or 4,294,967,296 addresses
• Address are assigned in ranges to
accommodate
 Large networks
 Medium size networks
 Small networks
• Convenient to break address into two parts
 Range number – network
 Individual numbers within the range - host
Internet Address
Address space originally defined into classes
Class A
0 netid
0
Net id = 0 - 127
hostid
8
31
- Maximum 128 Class A networks
- Each network could have 224 or
16,777,215 addresses or hosts
Class B
10
01
hostid
netid
16
Net id = 128 - 191
31
- Maximum 16,384 Class B networks
- Each has 65,536 addresses or nodes
Internet Address
Class C
110
netid
hostid
0
24
Net id = 192 - 223
31
- Maximum 2,097,152 Class C networks
- Each network has 28 or 256 addresses
Class D
1110
multicast
0
Class E
11110
0
Net id = 224 - 239
31
future
31
Netid and hostid
Internet Addresses
• It is common place to represent a 32 bit Internet
address in dotted notation
• Given a 32 bit address 0x826F27A2
We would write as 130.111.39.162
• Here 130.111 is the network address
39.162 is the host id
• The address in this network range
130.111.0.0 to 130.111.255.255
• Likewise, the 193.56.120.50 is part of the range
193.56.120.0 to 193.56.120.255
Special Internet Addresses
• By convention 0 means ‘this’
1 means ‘all’
All 0’s
This host
0’s
hostid
Host on this network
127
Anything
Loopback Address
Data sent to this address is returned
Never sent out on network
Special Internet Addresses
netid
0s
Refers to this network (netid)
Not assigned to any host
netid
1s
All hosts on this network (netid)
Called a directed broadcast
0s
1s
All host on local network
Called a limited broadcast
Addresses and Routing
• Devices that determine paths or routing
need only know about network addresses
• Only the destination network need be
concerned about the host address
• Devices that determine paths or routes are
usually called routers
• Routers must have tables entries, called a
routing table, for every network in order to
determine paths
Subnetting
• Some networks (Class A & B) are large
enough to warrant breakdown into smaller
groups, subnets
• An organization may be assigned a large
range (Class B) and may wish to allocate
to departments in smaller subnets
• To make internal routers treat these
subnets internally as separate networks
requires additional information
• Must specify which bits in the address
represents the network id
Subnetting
• To provide for subnetting addresses are
specified in two parts
 The address
 A mask – indicate which bits make up network
address
• Example:
130.111.32.150 is part of a class B
• We could break this into smaller networks
130.111.32.150
255.255.255.0
• 130.111.32 would be treated as a network id and
.150 as the host id within that network
Subnetting
• Specified in RFC 950
• Examples
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130.111.39.5
130.111.39.5
130.111.39.5
130.111.39.5
130.111.39.5
130.111.39.5
255.255.255.0
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.252
Subnetting
• Alternative notation – Slash notation
• Instead of specifying a mask, indicate how
many bits constitute the network address
 130.111.39.250 255.255.255.0
 130.111.39.250/24
• Thus, any Class B network could be
specified as a.b.c.d/16
Supernetting
• Much like subnetting a Class x network, we can
collect adjacent Class x networks to form larger
networks
• Consider the two Class C networks
193.240.88.0 255.255.255.0
193.240.89.0 255.255.255.0
Each of these is a network of 256 addresses
• We could group these into a single network as
follows
193.240.88.0 255.255.254.0
193.240.88.0/23
Determining Network/Host Address
255.255.0.0
141.14.72.24
AND
141.14.0.0
255.255.192.0
141.14.72.24
AND
141.14.64.0
Defining Subnets
• An organization is allocated a Class B
network 181.56.0.0
• The organization needs at least 1000
subnets
• If a common mask will be used for all
these subnets, the number must be a
power of 2.
• There will be 1024 subnets
• The mask will be 255.255.255.192
• Each subnet will have 64 addresses
Defining Subnets
Network ID
11111111 11111111 11111111 11000000
181.56.0.0
Subnet
Host address
(1024)
(64)
255.255.255.192
Defining Subnets
• What is the range of the first subnet?
 181.56.0.0
181.56.0.63
• What is the range of the second subnet?
 181.56.0.64
181.56.0.127
• What is the range of the last subnet?
 181.56.255.192
181.56.255.255
• What is the range of the 1023rd subnet?
 181.56.255.128
181.56.255.127
Classfull Addressing
• Class A networks are too large which
results into wasted address space
• Class B are also too large for many
organizations
• Class C networks are too small, requiring
multiple allocations to the same
organization
• In the early 90s, it became clear that this
method of address space allocation would
lead to early depletion of addresses
Classless Interdomain Routing
(CIDR)
• To preserve address space, a new method
of assigning space was developed in 1993
• Groups of unassigned address were
allocated regionally (RFC 1466)
• New allocation scheme provided for
allocation of variable length blocks of
addresses
• Going forward, allocations would no longer
be done by Class
• Allocation scheme defined in RFC 1518
Classless Interdomain Routing
• Address blocks are sized by powers of 2
• Blocks of size 2,4,8,…., 256, 512, 1024… can
be assigned
• Stating address must be divisible by the number
of addresses in the block
• The allocation is specified the same fashion as
subnets using slash notation
• Original allocations are maintained and folded
into this scheme
• Routers modified to accept and maintain their
routing tables in this way
Managing Address Space
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Blocks of addresses assigned to ISPs
ISPs assign subnets to customers
Assigned subnets can be of variable sizes
When customers change Service Provider,
they usually have to change address
space
• Usually, the ISP will assign large subnets
first, followed by smaller subnets
Variable size Subnetting
An ISP is granted a block of addresses starting with
190.100.0.0/16. The ISP needs to distribute these
addresses to three groups of customers as follows:
Group 1 has 64 customers; each needs 256 addresses
Group 2 has 128 customers; each needs 128
addresses.
Group3 has 128 customers; each needs 64 addresses.
Variable size Subnetting
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Group 1
For this group, each customer needs 256 addresses.
This means the suffix (host-id) length is 8
The prefix length (net-id) is then 32 - 8 = 24.
01: 190.100.0.0/24 190.100.0.255/24
02: 190.100.1.0/24 190.100.1.255/24
…………………………………..
64: 190.100.63.0/24190.100.63.255/24
Total = 64  256 = 16,384
Variable size Subnetting
• Group 2
• For this group, each customer needs 128 addresses.
This means the suffix length is 7 (27 = 128). The
prefix length is then 32 - 7 = 25. The addresses are:
• 001: 190.100.64.0/25
190.100.64.127/25
• 002: 190.100.64.128/25 190.100.64.255/25
• ……………………………………….
• 128: 190.100.127.128/25 190.100.127.255/25
• Total = 128  128 = 16,384
Variable size Subnetting
• Group 3
• For this group, each customer needs 64 addresses.
This means the suffix length is 6 (26 = 64). The
prefix length is then 32 - 6 = 26.
• 001:190.100.128.0/26 190.100.128.63/26
• 002:190.100.128.64/26 190.100.128.127/26
• …………………………
• 128:190.100.159.192/26 190.100.159.255/26
• Total = 128  64 = 8,192
UMS Managed Address Space
130.111.0.0/16
169.244.0.0/16
141.114.0.0/16
192.43.249.0/24
198.148.217.0/24
198.182.161.0/24
198.182.162.0/23
199.33.141.0/24
207.166.224.0/19
209.222.192.0/19
64.45.64.0/18
65.18.0.0/18
65.18.64.0/19
65.18.96.0/20
University of Maine System
Maine School and Library Network
State of Maine Government
Jackson Laboratories
Waterville K12
State of Maine Government
State of Maine Government
College of the Atlantic
University of Maine System
University of Maine System
University of Maine System
University of Maine System
University of Maine System
University of Maine System
Private Addresses
• Some organizations want to establish IP
networks internally, but not outside the
organization
• By convention, some address space is
allocated for this purpose
• These addresses are not accepted
(routed) on the Internet, but can be routed
internally
Private Addresses
• RFC 1918 defines this address space
10.0.0.0
172.16.0.0
192.168.0.0
to
to
to
10.255.255.255
172.31.255.255
192.168.255.255
IP addressing tools
Web tool for calculating subnet masks
http://library.mobrien.com/index.shtml
Tool for calculating subnet masks
ipcalc321.exe on course web site (Wildpackets)
Tool to look up ownership of IP address space
cyberkit - cyber30.zip on web site