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4: Network Layer 4a-

10: IP Basics

4: Network Layer 4a-

The Internet Network layer

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routing

table

Host, router network layer functions:

Routing protocols

• path selection
• RIP, OSPF, BGP

IP protocol

• addressing conventions
• datagram format
• packet handling conventions

ICMP protocol

• error reporting
• router “signaling”

Transport layer: TCP, UDP

Link layer

physical layer

Network

layer

4: Network Layer 4a-

Protocol stack:

packet forwarding

HTTP

TCP

IP

ethernet

Host A

IP

ethernet

Router R

link

HTTP

TCP

IP

ethernet

Router W

Host B

IP

link ethernet

4: Network Layer 4a-

IP Addressing

 IP address:

 32 bits

 network part (high order bits)

 host part (low order bits)

 Defined by class of IP address?

 Defined by subnet mask?

4: Network Layer 4a-

IP Addressing

How to find the

networks?

 device interfaces with same network part of IP address?

 can physically reach each other without intervening router?

223.1.1.

Interconnected

system consisting

of six “networks”

or one network

4: Network Layer 4a-

IP Addresses (Classes)

0 network^ host

10 network^ host

110 network^ host

1110 multicast address

A

B

C

D

class

1.0.0.0 to

128.0.0.0 to

192.0.0.0 to

224.0.0.0 to

32 bits

given notion of “network”, let’s re-examine IP addresses:

“class-full” addressing

Unicast

Multicast

E 1111 reserved

240.0.0.0 to

Reserved

4: Network Layer 4a-

IP Address Space Allocation

CAIDA 1998

4: Network Layer 4a-

Current Allocation

 Interesting to examine current IP address

space allocation (who has class A’s? Etc)

 Who has A’s?

 Computer companies around during initial

allocation (IBM, Apple)

 Universities (Stanford, MIT)

 Have A and still use other IP address blocks?

 CAIDA has info on complete allocation

4: Network Layer 4a-

Recall: How to get an IP

Address?

 Answer 1: Normally, answer is get an IP address

from your upstream provider

 This is essential to maintain efficient routing!

 Answer 2: If you need lots of IP addresses then

you can acquire your own block of them.

 IP address space is a scarce resource - must prove you have fully utilized a small block before can ask for a larger one and pay $$ (Jan 2002 - $2250/year for / and $18000/year for a /14)

4: Network Layer 4a-

How to get lots of IP

Addresses? Internet Registries

RIPE NCC (Riseaux IP Europiens Network

Coordination Centre) for Europe, Middle-East,

Africa

APNIC (Asia Pacific Network Information Centre )

for Asia and Pacific

ARIN (American Registry for Internet Numbers) for

the Americas, the Caribbean, sub-saharan Africa

LACNIC (Latin America and the Caribbean)

Note: Once again regional distribution is important

for efficient routing!

Can also get Autonomous System Numbers (ASNs)

from these registries

4: Network Layer 4a-

How to get a block of IP

addresses?From upstream provider

Network (network portion):

 get allocated portion of ISP’s address space:

ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/

Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/

Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/

Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/

... ….. …. ….

Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/

4: Network Layer 4a-

Hierarchical addressing: route aggregation

“Send me anything with addresses beginning 200.23.16.0/20”

Fly-By-Night-ISP

Organization 0

Organization 7

Internet

Organization 1

ISPs-R-Us “Send me anything with addresses beginning 199.31.0.0/16”

Organization 2

. . .

. . .

Hierarchical addressing allows efficient advertisement of routing

information:

4: Network Layer 4a-

IP Address Allocation

 CIDR is great but must work around existing

allocations of IP address space

 Company 1 has a /20 allocation and has given out sub portions of it to

other companies

 University has a full class B address

 Company 2 has a /23 allocation from some other class B

 ALL use the same upstream ISP – that ISP must advertise routes to all

these blocks that cannot be described with a simple CIDR network ID and

mask!

 Estimated reduction in routing table size with CIDR

 If IP addresses reallocated, CIDR applied to all, IP addresses reallocated

based on geographic and service provider divisions that current routing

tables with 10000+ entries could be reduced to 200 entries [Ford,

Rekhter and Brown 1993]

 How stable would that be though? Leases for all?

4: Network Layer 4a-

IP addresses: how to get one?

One more time 

 Hard-coded by system admin in a file

 Long with subnet mask, default gateway and DNS

server

 DHCP: Dynamic Host Configuration Protocol:

dynamically get network identity and neighborhood

info dynamically, “plug-and-play”