Lecture 2: The Internet Protocol · address, eg MAC addresses. They are enough within a LAN, but...

TSIN02 - Internetworking

© 2004 Image Coding Group, Linköpings Universitet

Lecture 2: The Internet Protocol

Literature:● Forouzan: ch 4-9 and ch 27


2

Outline

● About the network layer– Tasks– Addressing– Routing

● Protocols


3

Tasks of the network layer● Source to destination delivery of packets (across

multiple networks)● Logical addressing - addresses valid over network

borders● Routing● Fragmentation and reassembly


4

Logical vs Physical Addresses

● Each network interface card (NIC) has a physical address, eg MAC addresses. They are enough within a LAN, but give no routing help outside the local area.

● Logical addresses were created to help with communication between networks. Nodes within a LAN have neighbouring IP addresses. All traffic to the network can be routed using the common part of the addresses in the LAN, the network address.


5

Addressing● 32 bit addresses in IPv4 -->approx 4300 million

addresses available.● Dotted decimal notation, eg. 198.36.42.18● Sometimes hexadecimal notation is used, eg

0xC6242A12


6

Multihomed Devices


7

Classful Addressing● Addresses are assigned in blocks where the block

size is defined by the chosen class.● Classes A-E. The first byte defines the class.

Note! This is an obsolete addressing scheme! (They are still in use though...)

● Many organisations have been assigned more addresses than they need!

● One reason we are running out of addresses!


8

Classful addressing

Figures from Forouzan


9

NetID and HostID


10

Addresses and netmasks

● The network address is the first address in a block.

● The broadcast address is the last address in a block.

● A network mask is a 32 bit number such that the network address can be found by applying (bitwise, logical AND) the mask to any address in the block.


11

Using more addresses

Several techniques have been developed to lower the number of wasted addresses, eg.:

● Subnetting - divide a block into subnets using netmasks.

● Supernetting - combine blocks into supernets using netmasks.

● Classless addressing - no classes● In all cases the number of nets must be a

power of 2


12

With and without subnetting

Figure from Forouzan


13

Subnetting example

A company is given the site address 201.70.64.0 (class C). The company needs

six subnets. Design the subnets!


14

Example solution

● The number of 1s in the default mask is 24 (class C).

● The company needs six subnets. This is not a power of 2, so we will create eight subnets (8=23). We need three more 1s in the subnet mask, making it 27 in total

● The number of 0s is 32-27=5, so the mask is:11111111 11111111 11111111 11100000

or

255.255.255.224


15

Example solution



16

A Supernetwork



17

Supernet example

● We made a supernetwork out of 4 class C blocks. What is the supernet mask?– We are using 4 blocks. For 4 blocks we need to

change two 1s to 0s in the default mask. So the mask is:

11111111 11111111 11111100 00000000

or

255.255.252.0


18

Classless Addressing● Addresses are assigned in blocks of variable size.

One restriction is that the size of the block should be a power of 2.

● Slash notation - short form of network mask

– A.B.C.D/n where n is the number of 1s in the network mask.


19

Delivery and Routing● Direct or indirect delivery● Connection-oriented or connectionless service● Routing tables - gets huge

– next-hop– network specific– default routing– static or dynamic


20

Direct vs Indirect delivery



21

Next-hop routing



22

Network Specific Routing



23

Default Routing



24

Static or Dynamic Routing

● Static routing– routing table is entered manually

● Dynamic routing– routing table is periodically updated using a

dynamic routing protocol, like RIP, OSPF or BGP.


25

Protocols



26

ARP● Maps logical addresses to physical addresses. ● ARP requests are broadcasts on the LAN.● An ARP packet is encapsulated directly into a data

link frame.



27

ARP Communication



28

Proxy ARP



29

RARP● Maps physical addresses to logical addresses.● RARP requests are broadcast on the LAN● A RARP packet is encapsulated directly into a data

link frame● There are newer and better alternatives to RARP

– BOOTP– DHCP



30

RARP Communication



31

The Internet Protocol (IP)

● Unreliable● Connectionless● A “best effort” delivery service


32

Datagram



33

Fragmentation

● Maximum transfer unit (MTU)● Each data link layer protocol use its own frame format. ● Fragmentation needed when passing to a network

with a smaller MTU (IPv4).

MTU examples:

Hyperchannel - 65535 bytesEthernet - 1500 bytesPPP - 296 bytes


34

Options

Options are used for testing and debugging purposes



35

Checksum

Redundant information added that is used for error detection

The checksum is constructed as follows:

1. Divide the packet into k sections, each of n bits

2. All sections are added together using one's complement arithmetic. (We will look at this during Class 1)

3. The result is complemented to make the checksum


36

ICMP● Messages are encapsulated in IP datagrams.

● Two types of messages:

– Error reporting

● Dest. unreachable

● Source quench

● Time exceeded

● Parameter problems

● Redirection

– Query

● Echo request and reply

● Timestamp request and reply

● Address-mask request and reply

● Router solicitation and advertisement



37

IPv6

● Addressing● Packet format● Extension headers● Difference from IPv4● Transition from IPv4 to IPv6


38

IPv6: Addressing

There is a new addressing system in IPv6:– 128 bit addresses– new notation (hexadecimal colon notation)

eg. FDEC:BA33:0000:0000:FFCD:03F1:0000:0001( or FDEC:BA33::FFCD:3F1:0:1)

– slash notation supported– Three types of addresses

– unicast– anycast– multicast

– Address structure Type Prefix Rest of address

128 bits

variable



39

Address Space Assignments

Type Prefix Type Fraction0000 0000 Reserved 1/256010 Provider based addresses 1/2561111 1110 10 Link local addresses 1/10241111 1110 11 Site local addresses 1/10241111 1111 Multicast addresses 1/256

●Unspecified●Loopback●IPv4

●Type 3 bits●Registry id 5bits●Provider id 16 bits●Subscriber id 24 bits●Subnet id 32 bits●Node id 48 bits


40

IPv6 Datagram



41

Datagram format



42

Extension headers (options)– Hop-by-hop option

● Pad1● PadN● Jumbo payload

– Source routing– Fragmentation– Authentication– Encrypted Security Payload– Destination Option– (No Next Header)


43

Extension Header Format



44

Difference from IPv4

● (Much) larger address space● Better header format● New options● Prepared for extensions● Support for resource allocation (flow label)● Support for more security


45

Transition Strategies

● Dual stack - hosts keep a dual stack of protocols, thus running IPv4 and IPv6 simultaneously.

● Tunneling - passing IPv6 packets through a region where IPv4 is used.– Automatic– Configured

● Header translation - when only a few hosts use IPv4


46

ICMPv6

● Message format● Difference from ICMPv4


47

What's new?● ARP and IGMP included in ICMPv6

● RARP dropped

● Error report● Source quench report dropped● Packet too big report added

IP

ICMPIGMP

ARP RARP

IP

ICMP

Network layer in version 4 Network layer in version 6

- Query- Timestamp query dropped- Address mask query dropped

Figures from Forouzan


48

ICMPv6 message format



49

ICMPv6 Error Messages

● Destination Unreachable● Packet Too Big● Time Exceeded● Parameter Problem

Lecture 2: The Internet Protocol · address, eg MAC addresses. They are enough within a LAN, but...

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