EE 122: IP Addressing - University of California, Berkeleyinst.eecs.berkeley.edu/~ee122/fa08/notes/07-Addressingx2.pdf · 4 7 IP Address and a 24-bit Subnet Mask 0000110000100010

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EE 122: IP Addressing

Ion Stoica (and Brighten Godfrey)

TAs: Lucian Popa, David Zats and GaneshAnanthanarayanan

http://inst.eecs.berkeley.edu/~ee122/

(Materials with thanks to Vern Paxson, Jennifer Rexford,and colleagues at UC Berkeley)

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Goals of Today’s Lecture

� IP addresses

� Dotted-quad notation

� IP prefixes for aggregation

� Classful addresses

� Classless InterDomain Routing (CIDR)

� Special-purpose address blocks

� Address allocation

� Hierarchy by which address blocks are given out

� Finding information about an allocation

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Designing IP’s Addresses

� Question #1: what should an address be associated with?

� E.g., a telephone number is associated not with a person but with a handset

� Question #2: what structure should addresses have? What are the implications of different types of structure?

� Question #3: who determines the particular addresses used in the global Internet? What are the implications of how this is done?

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IP Addresses (IPv4)

� A unique 32-bit number

� Identifies an interface (on a host, on a router, …)

� Represented in dotted-quad notation. E.g, 12.34.158.5:

00001100 00100010 10011110 00000101

12 34 158 5

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Hierarchical Addressing in U.S.

Mail

� Addressing in the U.S. mail

� Zip code: 15232

� Street: Forbes Avenue

� Building on street: 5000

� Apartment: 61B

� Name of occupant: Ion Stoica

� Forwarding the U.S. mail

� Deliver letter to the post office in the zip code

� Assign letter to mailman covering the street

� Drop letter into mailbox for the building/room

� Give letter to the appropriate person

???

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Hierarchical Addressing: IP

Prefixes

� Divided into network (left) & host portions (right)

� 12.34.158.0/24 is a 24-bit prefix with 29 addresses

� Terminology: “Slash 24”

00001100 00100010 10011110 00000101

Network (24 bits) Host (8 bits)

12 34 158 5

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IP Address and a 24-bit Subnet Mask

00001100 00100010 10011110 00000101

12 34 158 5

11111111 11111111 11111111 00000000

255 255 255 0

Address

Mask

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Addressing Hosts in the Internet

� The Internet is an “inter-network”

� Used to connect networks together, not hosts

� Needs a way to address a network (i.e., group of hosts)

host host host

LAN 1

...host host host

LAN 2

...

router router routerWAN WAN

LAN = Local Area Network

WAN = Wide Area Network

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Routers

� Router consists of� Set of input interfaces where packets arrive� Set of output interfaces from which packets depart� Some form of interconnect connecting inputs to outputs

� Router implements� Forward packet to corresponding output interface� Manage bandwidth and buffer space resources

host host host

LAN 1

...host host host

LAN 2

...


Router

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Forwarding Table

� Store a mapping between IP addresses and output interfaces

� Forward an incoming packet based on its destination address

……

31.2.3.6

11.2.3.5

1

21.2.3.5

1.2.3.4

1.2.3.4 2

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Scalability Challenge

� Suppose hosts had arbitrary addresses

� Then every router would need a lot of information

� …to know how to direct packets toward the host

host host host

LAN 1

...host host host

LAN 2

...


1.2.3.4 5.6.7.8 2.4.6.8 1.2.3.5 5.6.7.9 2.4.6.9

1.2.3.4

1.2.3.5

forwarding table

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Scalability Improved

� Number related hosts from a common subnet

� 1.2.3.0/24 on the left LAN

� 5.6.7.0/24 on the right LAN

host host host

LAN 1

...host host host

LAN 2

...


1.2.3.4 1.2.3.7 1.2.3.156 5.6.7.8 5.6.7.9 5.6.7.212

1.2.3.0/24

5.6.7.0/24

forwarding table

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Easy to Add New Hosts

� No need to update the routers

� E.g., adding a new host 5.6.7.213 on the right

� Doesn’t require adding a new forwarding entry

host host host

LAN 1

...host host host

LAN 2

...


1.2.3.4 1.2.3.7 1.2.3.156 5.6.7.8 5.6.7.9 5.6.7.212

1.2.3.0/24

5.6.7.0/24

forwarding table

host

5.6.7.213

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Classful Addressing

� Class A: if first byte in [0..127], assume /8 (top bit = 0)

� Very large blocks (e.g., MIT has 18.0.0.0/8)

� Class B: first byte in [128..191] ⇒ assume /16 (top bits = 10)

� Large blocks (e.g,. UCB has* 128.32.0.0/16)

� Class C: [192..223] ⇒ assume /24 (top bits = 110)

� Small blocks (e.g., ICIR has 192.150.187.0/24)

� The “swamp” (many European networks, due to history)

0******* ******** ******** ********

10****** ******** ******** ********

110***** ******** ******** ********

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Classful Addressing (cont’d)

� Class D: [224..239] (top bits 1110)

� Multicast groups

� Class E: [240..255] (top bits 11110)

� Reserved for future use

� What problems can classful addressing lead to?

� Only comes in 3 sizes

� Routers can end up knowing about a lot of class C’s

1110**** ******** ******** ********

11110*** ******** ******** ********

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Classless Inter-Domain Routing (CIDR)

IP Address : 12.4.0.0 IP Mask: 255.254.0.0

00001100 00000100 00000000 00000000

11111111 11111110 00000000 00000000

Address

Mask

for hosts Network Prefix

Use arbitrary length prefixesUse two 32-bit numbers to represent a network.

Network number = IP address + Mask

Written as 12.4.0.0/15 or 12.4/15

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CIDR: Hierarchal Address Allocation

12.0.0.0/8

12.0.0.0/15

12.253.0.0/16

12.2.0.0/16

12.3.0.0/16

:

:

12.3.0.0/2212.3.4.0/24

:

:12.3.254.0/23

12.253.0.0/1912.253.32.0/1912.253.64.0/19

12.253.64.108/3012.253.96.0/1812.253.128.0/17

:

:

:

� Prefixes are key to Internet scalability

� Addresses allocated in contiguous chunks (prefixes)

� Routing protocols and packet forwarding based on prefixes

:

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Scalability: Address Aggregation

Provider is given 201.10.0.0/21 (201.10.0.x .. 201.10.7.x)

201.10.0.0/22 201.10.4.0/24 201.10.5.0/24 201.10.6.0/23

Provider

Routers in the rest of the Internet just need to know

how to reach 201.10.0.0/21. The provider can direct the

IP packets to the appropriate customer.

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But, Aggregation Not Always

Possible

201.10.0.0/21

201.10.0.0/22 201.10.4.0/24 201.10.5.0/24 201.10.6.0/23

Provider 1 Provider 2

Multi-homed customer with 201.10.6.0/23 has two

providers. Other parts of the Internet need to know how

to reach these destinations through both providers.

⇒⇒⇒⇒ /23 route must be globally visible

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Growth in Routed Prefixes (1989-2005)

Initial growth super-linear; no aggregation

Advent of CIDR allows aggregation: linear growth

Internet boom: multihoming drives superlinear growth

Dot-com implosion; Internet bubble bursts

Back in business

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Special-Purpose Address Blocks� Private addresses

� By agreement, not routed in the public Internet� For networks not meant for general Internet connectivity� Blocks: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16

� Link-local� By agreement, not forwarded by any router� Used for single-link communication only� Intent: autoconfiguration (especially when DHCP fails)� Block: 169.254.0.0/16

� Loopback� Address blocks that refer to the local machine� Block: 127.0.0.0/8

� Usually only 127.0.0.1/32 is used

� Limited broadcast� Sent to every host attached to the local network� Block: 255.255.255.255/32

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Scalability Through Non-Uniform

Hierarchy

Summary:

� Hierarchical addressing

� Critical for scalable system

� Don’t require everyone to know everyone else

� Reduces amount of updating when something changes

� Non-uniform hierarchy

� Useful for heterogeneous networks of different sizes

� Initial class-based addressing was far too coarse

� Classless InterDomain Routing (CIDR) gains much more flexibility

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5 Minute Break

Questions Before We Proceed?

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Address Allocation

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Obtaining a Block of Addresses

� Separation of control� Prefix: assigned to an institution

� Addresses: assigned by the institution to their nodes

� Who assigns prefixes?� Internet Corporation for Assigned Names and Numbers

� Allocates large address blocks to Regional Internet Registries

� ICANN is politically charged

� Regional Internet Registries (RIRs)� E.g., ARIN (American Registry for Internet Numbers)

� Allocates address blocks within their regions

� Allocated to Internet Service Providers and large institutions ($$)

� Internet Service Providers (ISPs)� Allocate address blocks to their customers (could be recursive)

� Often w/o charge

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Figuring Out Who Owns an Address

� Address registries� Public record of address allocations

� Internet Service Providers (ISPs) should update when giving addresses to customers

� However, records are notoriously out-of-date

� Ways to query� UNIX: “whois –h whois.arin.net 169.229.60.27”

� http://www.arin.net/whois/

� http://www.geektools.com/whois.php

� …

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Example Output for 169.229.60.27

University of California, Office of the President UCNET-BLK (NET-169-229-0-0-1)

169.229.0.0 - 169.233.255.255

University of California at Berkeley ISTDATA

(NET-169-229-0-0-2)

169.229.0.0 - 169.229.255.255

• ISTDATA – Information Services and Technology (IST) -Data Communication and Network Services

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Are 32-bit Addresses Enough?

� Not all that many unique addresses� 232 = 4,294,967,296 (just over four billion)

� Plus, some (many) reserved for special purposes

� And, addresses are allocated in larger blocks

� And, many devices need IP addresses� Computers, PDAs, routers, tanks, toasters, …

� Long-term solution (perhaps): larger address space� IPv6 has 128-bit addresses (2128 = 3.403 × 1038)

� Short-term solutions: limping along with IPv4� Private addresses

� Network address translation (NAT)

� Dynamically-assigned addresses (DHCP)

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Network Address Translation (NAT)

� Before NAT…

� Every machine connected to the Internet had a unique IP address

1.2.3.4

1.2.3.5

5.6.7.8

LAN

Clients

Server

Internet

dest addr src addrdst port

src port

5.6.7.8 1.2.3.4 80 10015.6.7.8 1.2.3.4 80 1001

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Network Address Translation (NAT)

� Before NAT…

� Every machine connected to the Internet had a unique IP address

1.2.3.4

1.2.3.5

5.6.7.8

LAN

Clients

Server

Internet1.2.3.45.6.7.880 1001

1.2.3.45.6.7.880 1001

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Network Address Translation (cont’d)

� Independently assign addresses to machines behind same NAT

� Usually in address block 192.168.0.0/16

� Use port numbers to multiplex demultiplex internal addresses

192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

5.6.7.8 192.2.3.4 80 1001

5.6.7.8 192.2.3.4 80 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

5.6.7.8 1.2.3.4 80 2000

5.6.7.8 192.2.3.4 80 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

5.6.7.8 1.2.3.4 80 2000

5.6.7.8 1.2.3.4 80 2000

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

1.2.3.45.6.7.880 2000

1.2.3.45.6.7.880 2000

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

1.2.3.45.6.7.880 2000

5.6.7.8 192.2.3.480 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

5.6.7.8 192.2.3.480 1001

5.6.7.8 192.2.3.480 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

Internet

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

192.2.3.5:1001 1.2.3.4:2001

5.6.7.8 192.2.3.5 80 1001

5.6.7.8 192.2.3.5 80 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

5.6.7.8 1.2.3.4 80 2001

192.2.3.5:1001 1.2.3.4:2001

5.6.7.8 192.2.3.5 80 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

5.6.7.8 1.2.3.4 80 2001

192.2.3.5:1001 1.2.3.4:2001

5.6.7.8 1.2.3.4 80 2001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

192.2.3.5:1001 1.2.3.4:2001

1.2.3.45.6.7.880 2001 1.2.3.45.6.7.880 2001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

192.2.3.5:1001 1.2.3.4:2001

1.2.3.45.6.7.880 2001

5.6.7.8 192.2.3.580 1001

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192.2.3.4

192.2.3.5

5.6.7.8

Clients

Server

NAT

1.2.3.4

192.2.3.4:1001 1.2.3.4:2000

192.2.3.5:1001 1.2.3.4:2001

5.6.7.8 192.2.3.580 1001

5.6.7.8 192.2.3.580 1001

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Hard Policy Questions

� How much address space per geographic region?� Equal amount per country?

� Proportional to the population?

� What about addresses already allocated?

� Address space portability?� Keep your address block when you change providers?

� Pro: avoid having to renumber your equipment

� Con: reduces the effectiveness of address aggregation

� Keeping the address registries up to date?� What about mergers and acquisitions?

� Delegation of address blocks to customers?

� As a result, the registries are often out of date

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Summary of IP Addressing

� 32-bit numbers identify interfaces

� Allocated in prefixes

� Non-uniform hierarchy for scalability and flexibility

� Routing is based on CIDR

� A number of special-purpose blocks reserved

� Address allocation:

� ICANN ⇒ RIR ⇒ ISP ⇒ customer network ⇒ host

� Issues to be covered later� How hosts get their addresses (DHCP)

� How to map from an IP address to a link address (ARP)

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Next Lecture

� IP Forwarding; Transport protocols

� Read K&R: 3-3.4 (pp 195-240)

EE 122: IP Addressing - University of California, Berkeleyinst.eecs.berkeley.edu/~ee122/fa08/notes/07-Addressingx2.pdf · 4 7 IP Address and a 24-bit Subnet Mask 0000110000100010

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