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

Physical LayerTwisted pairsFiber Optics

encoding

CSMA/CDIEEE802.3

Pt-to-PtHDLCPPP

IEEE 802.11

Network Layer

Addressing Routing Packetizing

Network Layer

• There are and have been many network layer protocols 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

• 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

Atlanta

Indianapolis

Kansas City

Denver

Los Angeles

Sacramento

Seattle

Abilene Core Node

Abilene Access Node

Operational January 1999

Houston

Cleveland

New York

Internet today

Internet Standards Bodies

Internet Society (ISOC)http://www.isoc.org

Internet Architecture Board (IAB)http://www.iab.org

Internet Engineering Task Force(IETF)

http://www.ietf.org

Internet Research Task Force(IRTF)

http://www.irtf.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 repositoryhttp://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• APNIC (Asia Pacific Network Information Centre) • ARIN (American Registry for Internet Numbers) • RIPE NCC (Réseaux IP Européens)• LACNIC (Regional Latin-American and Caribbean IP Addres

s 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 AddressAddress space originally defined into classes

Class A

- Maximum 128 Class A networks

- Each network could have 224 or 16,777,215 addresses or hosts

Class B

- Maximum 16,384 Class B networks

- Each has 65,536 addresses or nodes

0 netid hostid8 310

1 netid hostid00 1 16 31

Net id = 0 - 127

Net id = 128 - 191

Internet Address

Class C

- Maximum 2,097,152 Class C networks

- Each network has 28 or 256 addresses

Class D

Class E

Net id = 192 - 223

Net id = 224 - 239

1 netid hostid310

1024

1110 multicast0 31

11110 future310

Netid and hostid

Internet Addresses

• It is common place to represent a 32 bit Internet address in dotted notation

• Given a 32 bit address 0x826F27A2We 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 range130.111.0.0 to 130.111.255.255

• Likewise, the 193.56.120.50 is part of the range193.56.120.0 to 193.56.120.255

Special Internet Addresses

• By convention 0 means ‘this’

1 means ‘all’

All 0’s

0’s hostid

127 Anything

This host

Host on this network

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 networks130.111.32.150 255.255.255.0

• 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 130.111.39.5 255.255.255.0 130.111.39.5 255.255.255.128 130.111.39.5 255.255.255.192 130.111.39.5 255.255.255.224 130.111.39.5 255.255.255.240 130.111.39.5 255.255.255.252

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 networks193.240.88.0 255.255.255.0

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

141.14.72.24AND

141.14.0.0

255.255.0.0

141.14.72.24AND

141.14.64.0

255.255.192.0

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

11111111 11111111 11111111 11000000

181.56.0.0 255.255.255.192

Host address

(64)

Subnet

(1024)

Network ID

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

• 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 addressesGroup 2 has 128 customers; each needs 128 addresses.Group3 has 128 customers; each needs 64 addresses.

Variable size Subnetting

• 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: 190.100.63.0/24190.100.63.255/24• 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 University of Maine System

169.244.0.0/16 Maine School and Library Network

141.114.0.0/16 State of Maine Government

192.43.249.0/24 Jackson Laboratories

198.148.217.0/24 Waterville K12

198.182.161.0/24 State of Maine Government

198.182.162.0/23 State of Maine Government

199.33.141.0/24 College of the Atlantic

207.166.224.0/19 University of Maine System

209.222.192.0/19 University of Maine System

64.45.64.0/18 University of Maine System

65.18.0.0/18 University of Maine System

65.18.64.0/19 University of Maine System

65.18.96.0/20 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 to 10.255.255.255

172.16.0.0 to 172.31.255.255

192.168.0.0 to 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