IP (Internet Protocol)

TCP/IP Protocol Suite(Stack) is based on 3 conceptual layers and

The Network Access Layer

Application Services--OSI 5, 6, 7

Reliable/unreliable Transport Service--OSI 4

Connectionless Packet Delivery Service--OSI 3

Network Access Layer--(undefined) OSI 1, 2--in other words, any network connection can be used; Ethernet, token Ring, FDDI, ATM, Frame Relay, X.25, PPP, …..

TCP/IP Protocol Suite diagram showing the interactions between layers & the Service Access Points

IP(Internet Protocol)

· Provides Connectionless Service(Datagram Service)

· IP forms and Delivers IP packets

· Unreliable, Best-effort Delivery System

· Packets may be

· Lost--hit by noice

· Duplicated--TCP timeout occurs and a packet is resent

· Delayed--taking long time to reach destination

· Delivered out-of-order--packets taking different routes

· Routes packets

An example of WAN connections:

Connection structure in terms of protocols for the above network

IP datagram format(From RFC 791--IPv4)

http://www.csl.sony.co.jp/cgi-bin/hyperrfc?rfc791.txt

 0 1 2 3 
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
Example Internet Datagram Header
 

A datagram is a variable length packet made up of 2 parts—Header(20 – 60 bytes) and Data

Version

Current version is 4. Supposed to be replaced by version 6(IPv6 or IPng=IP Next Generation)

IHL(IP Header Length)

Indicates how many 4-byte words for the header portion--Header can be between 20bytes to 60 bytes depending upon the length of the Options field

Type of Service

Defines how the datagram should be handled by routers

Bits 0-2: Precedence.
Bit 3: 0 = Normal Delay, 1 = Low Delay.
Bits 4: 0 = Normal Throughput, 1 = High Throughput.
Bits 5: 0 = Normal Relibility, 1 = High Relibility.
Bit 6-7: Reserved for Future Use.
 
  0 1 2  3 4 5 6 7
 +-----+-----+-----+-----+-----+-----+-----+-----+
 | | | | | | |
 | PRECEDENCE | D | T | R | 0 | 0 |
 | | | | | | |
  +-----+-----+-----+-----+-----+-----+-----+-----+
 
Precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
 
The use of the Delay, Throughput, and Reliability indications may increase the cost (in some sense) of the service. In many networks
better performance for one of these parameters is coupled with worse
performance on another. Except for very unusual cases at most two
of these three indications should be set.
The type of service is used to specify the treatment of the datagram
during its transmission through the internet system. Example
mappings of the internet type of service to the actual service
provided on networks such as AUTODIN II, ARPANET, SATNET, and PRNET
is given in “Service Mappings” [8].

D bit = low delay request

T bit = high throughput

R bit = high reliability

These requests are hints to routing algorithm but not as demands

A router tries to closely accommodate the request(in choosing alternatives among possible routes) but it is not guaranteed

Typical usages of TOS

-------------------------------------------------------------------------

Protocol TOS Bits Description

-------------------------------------------------------------------------

ICMP 0000 Normal

NNTP 0001 Minimize cost

IGP 0010 Maximum reliability

TELNET 1000 Minimize delay

FTP(data) 0100 Maximize throughput

FTP(control) 1000 Minimize delay

……

……

Total Length

Total length in bytes including the Header

(Length of data = Total length - Length of Header)

Identification

Unique number(16 bits) for a datagram—generated by the host and incremented for each datagram

This field and Fragment Offset field are used for fragmentation & reassembly of datagrams.

Maximum Transfer Unit(MTU)—Each data link(LAN connection) has its own frame format and a maximum allowed size:

Protocol MTU(Bytes)

Hyperchannel 65,536

Token ring(16Mbps) 17,914

Token ring(4Mbps) 4,464

FDDI 4,352

Ethernet 1,500

X.25 576

PPP 296

When a datagram travels through different networks, the original size can not be accommodated on some paths, so Fragmentation occurs

· In Internet, once DG fragmented, it stays fragmented(intermediate routers do not reassemble fragments)

· At destination host, fragments are assembled using (Identification + Offset) with reassembly timer(if timer expires, drop the DG-->lost DG)

Fragmentation Control

· Identification=unique DG ID(same for all fragments) set by sending computer

· Fragment Offset=used for reassembly at destination

· A datagram can be fragmented by the source host or any router in the path

Flags

· First bit is not used

· D bit =Do not fragment

(ex. a computer runs small bootstrap sequence to use internet to get initial bootstrap program., then responder sends a memory image which must not be fragmented)

· If a router has to fragment for a packet with D=1, it drops the DG and notify sender

· M bit =More fragments(more coming)

· Can a fragment be fragmented again? Yes

Time to Live(TTL)

Set to a maximum by sender and each router decrements by 1 or #of seconds

If becomes 0, drop and notify source(by a router)

Usually TTL is set for 32 or 64

Protocol

This field specifies the high-level protocol that uses IP’s service(ex. TCP, UDP, ICMP, IGMP). Using this field, the receiving IP module knows to which protocol the datagram should be delivered.

Value Protocol

1 ICMP

2 IGMP

6 TCP

8 EGP

17 UDP

41 IPv6

89 OSPF

Header Checksum

1’s complement of sum(in 1’s comp arithmetic) of 16 bits--Checks only hearder

Adv=Usage of simple error checking reduces router overhead

Disadv=corrupted data will pass undetected

Source & Destination Address

IP addresses for source host and destination host

IP OPTIONS field

· Primarily for network testing & debugging

· COPY bit=Option must be copied to all fragments

· OPTION CLASS

· 0=DG/Network control

· 1=Reserved for future

· 2=Debugging & Measurement

· 3=Reserved for future

Option Op# Desc

0 2 Security Restrictions

0 3 Loose source routing

0 7 Trace route

0 9 Strict source routing

2 4 Timestamp along route

IP Addresses and Subnet Masks

IP ADDRESSES are used to route information (packets) through the Internet

Each packet contains both the source IP address and the destination IP address of a specific computer (host)--A computer on Internet must have a unique IP address during its connection

An IP address is 32 bits (4 bytes) long, and consists of two parts:

* netid

* hostid

 
 MSB LSB
 --------------------------------------
 | netid | host id |
 --------------------------------------
 

32 bit binary numbers are written in decimal form--called Dotted Decimal Notation--e.g 132.241.158.33

IP Address Classes--5 Classes A, B, C, D, E

(This classification is sometimes called as “Classful Internet Addresses--

in contrast to “CIDR”(Classless Interdomain Routing))

* class A

· a small number of huge networks (up to 16,777,214 hosts)

· first octet is 0-127 (i.e. first bit is 0)

· example: 26.104.0.19

* class B

· a large number of large networks (up to 65,534 hosts)

· first octet is 128-191 (i.e. first two bits are 10)

· example: 129.82.100.64

* class C

· a huge number of small networks (up to 254 hosts)

· first octet is 192-223 (i.e. first three bits are 110)

· example: 192.178.16.1

* class D

· first octet is 224 or greater

· used for “multicast” address--group address

· first octet is 224-239(i.e. first four bits are 1110)

* class E

· first octet is 240 or greater

· not given to the general public--Reserved for special use

· first octet is 240-255(i.e. first four bits are 1111)

Host computers and routers must have IP addresses to communicate over Internet

(Except for the routers that are connected as point-to-point)

Some host computers may have more than one IP addresses--called “Multihomed”

Special Addresses

Some parts of the addresses in class A, B, C are used for special addresses

---------------------------------------------------------------------------------------------------------------

Special Address Netid Hostid Source or Destination

---------------------------------------------------------------------------------------------------------------

Network address Specific All 0s None

(e.g. 132.241.158.0 is the subnet’s address for the LAN in OCNL340 lab)

---------------------------------------------------------------------------------------------------------------

Direct broadcast address Specific All 1s Destination

(This is used by a router to send a packet to all hosts in a subnet)

---------------------------------------------------------------------------------------------------------------

Limited broadcast address All 1s All 1s Destination

(A broadcast address for a subnet--It is used when a host wants to send a message to

all the hosts in the local subnet--routers will not pass this to other subnets)

---------------------------------------------------------------------------------------------------------------

This host on this network All 0s All 0s Source

(All 0s designate “this host on this network”--used by a host when it does not know

it’s own IP address)

---------------------------------------------------------------------------------------------------------------

Specific host on this network All 0s Specific Destination

(It is used by a host to send a message to another host on the same subnet-- Routers will

not process this kind)

---------------------------------------------------------------------------------------------------------------

Loopback address 127 Any Destination

(It is used to test IP software on the machine)

Depending upon their usage, IP addresses can be classified into 3 categories:

Unicast Address: One-to-one

Multicast Address: One-to-many

Broadcast Address: One-to-all

IP Addresses are depleted(running out)

4bytes = 4.3 billion--much less than human population(6 billion)

Class A and Class B IP addresses are no longer being given out--Internet Address space is running out!

At current rate the entire address space will be exhausted around 2008

“32bits should be enough address space for Internet” Vinton Cerf, 1977

(Vinton Cerf is known as “Father of Internet”)

Solutions:

· CIDR(Classless Internet Domain Routing)

http://www.csl.sony.co.jp/cgi-bin/hyperrfc?rfc1519.txt

· NAT(Network Address Translation)

http://www.csl.sony.co.jp/cgi-bin/hyperrfc?rfc1631.txt

· IPng(IPv6)

http://www.csl.sony.co.jp/cgi-bin/hyperrfc?2460

A class C address can have only 254 IP addresses, so for an organization which needs more than 254 addresses, one class C space is not enough.

For this purpose, class C addresses are being given in (CIDR) contiguous blocks, to ease the burden on routers of looking up addresses

* also, a single class C can be used to span multiple domains (sites), with a sum of hosts less than or equal to 254

IPv6 (version 6) contains an expanded address space (128 bits) - a huge

number of network addresses

http://www.ipv6.org/

Current solutions such as CIDR & NAT have problems:

CIDR: Limited space from the beginning, complexity in routers

NAT: Unidirectional communication--Stations in enclosed network can initiate

connections but computers outside the NAT cannot initiate the connection---no bi-directional

connections

Some technologies demand unique IP addresses for bi-directional connections such as IpSec

* Uses 128 bits -- 3.4*10**38---Class A address space for all sites

* Uses Hexadecimal notation: EX. 3FF3:0008:1234:0248:97EF:FE40:CFAB:0501

* IPv6 is NAT-free--end-to-end Bi-directional connections

*Transition from IPv4 to IPv6

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