ccna 1 v3.11 module 9ocw.dongyang.ac.kr/cms_ocw/network/435/note/5_10.pdf · ccna1 / 1st semester,...

1© 2007, Jae-sul Lee. All rights reserved.

TCP/IP Protocol Suite and IP Addressing

CCNA 1 v3.11 Module 9

22CCNA1 / 1st semester, 2007Network Information & Communication Program,

Dongyang Technical College

Agenda

9.1 Introduction to TCP/IP

9.2 Internet Addresses

9.3 Obtaining an IP address • Networking protocols for Layer 3 or above• Basics of the TCP/IP model• The role of the IP in the TCP/IP network• Concept of the IP address, IP address architecture, subnetting• How an IP address can be assigned to a device• How the MAC address of a device can be known, given the IP

address of that device



Overview• The Internet is based on the TCP/IP protocol suite

– TCP/IP is ideal for the decentralized and robust Internet – Many common protocols were designed based on the four-layer

TCP/IP model

• TCP/IP and OSI network models – Each model uses its own structure to explain how a network works– Be familiar with both models to understand how a network

functions

• The IP address– A unique identifier for any device on the Internet– Routers use a Layer 3 protocol called the IP protocol to find the

best route to that device



Overview• Network address space

– Current version of IP (IPv4) has the address space of 232

– IP addresses are classified into class A, B, C, D, and E

– Explosive growth of the Internet has threatened to deplete the supply of IP addresses

– Some solutions includes subnets, network address translation (NAT), and private addresses

– Ultimate solutions is IPv6

• Assigning the IP address to a device– Static assignment

– Dynamic assignment



Module objectives• Students who complete this module should be able to perform the following tasks:

– Explain why the Internet was developed and how TCP/IP fits the design of the Internet

– List the four layers of the TCP/IP model – Describe the functions of each layer of the TCP/IP model – Compare the OSI model and the TCP/IP model– Describe the function and structure of IP addresses– Explain the difference between public and private addressing– Understand the function of reserved IP addresses– Understand why subnetting is necessary – Explain the use of static and dynamic addressing for a device – Understand how dynamic addresses can be assigned with RARP, BootP,

and DHCP– Use ARP to obtain the MAC address to send a packet to another device – Understand the issues related to addressing between networks





9.3 Obtaining an IP address

• TCP/IP is the 4-layer protocol suit for the Internet• The role of each TCP/IP layer in networking• The comparison between TCP/IP and OSI layers• The growth of the network to the Internet and its operation



Outlines9.1.1 History and future of TCP/IP

9.1.2 Application layer

9.1.3 Transport layer

9.1.4 Internet layer

9.1.5 Network access layer

9.1.6 The OSI model and the TCP/IP model

9.1.7 Internet architecture



History and future of TCP/IP • The Internet is initiated by the U.S. Department of Defense

(DoD) – Required reliable data transmission to any destination on the

network under any circumstances

– The creation of the TCP/IP model helped to solve this difficult design problem

– The TCP/IP model has since become the standard on which the Internet is based

– The present version of TCP/IP was standardized in Sep. 1981



Application layer • The role of the application layer

– Handles high-level protocols, representation, encoding, and dialog control in one layer

Copyrighted material is cleared



Application layer




Transport layer • The role of the transport layer

– Provides a logical end-to-end connectivity between host applications

• End-to-end means from the source host to the destination host – Does not involve the intermediate route between each end

– The route is selected at the Internet layer

• Provide end-to-end control and reliability– Segmentation of the upper layer (application layer) data into the same

data stream

– Flow control of the data stream

– Error control of the stream

– Reassembly of the data segments

• Uses sliding windows, sequence numbers, and acknowledgments




Transport layer • Transport layer protocols

– TCP (connection-oriented) & UDP (connectionless)• Segment upper-layer application data

• Send segments from one end device to another

• The functions of TCP– Establish end-to-end operations

– Provide flow control through the use of sliding windows

– Ensure reliability through the use of sequence numbers and acknowledgments



Transport layer




Internet layer • The role of the Internet layer

– Select the best path through the network for packets to travel • Best path determination and packet switching occur at this layer

• Internet layer protocols1. Internet Protocol (IP)

• Provides connectionless, best-effort delivery routing of packets. – Looks for the best path to the destination for each packet. – Data integrity is not guaranteed

2. Internet Control Message Protocol (ICMP) • Provides control and messaging capabilities

3. Address Resolution Protocol (ARP) • Determines the MAC address for known IP addresses.

4. Reverse Address Resolution Protocol (RARP) • Assigns an IP address for an NIC with the known MAC address.



Internet layer



Internet layer • Operation of the IP

– Defines a packet and an addressing scheme

– Transfers data between the Internet layer and network access layer

– Routes packets to remote hosts

• Characteristics of the IP– Does not guarantee reliability (best-effort)

• No error checking or correction

– Reliability is provided by the upper layers



Internet layer




Network access layer • The network access layer

– Also called the host-to-network layer– Includes the LAN and WAN technology details (OSI layer 1 & 2)

• Ethernet, token ring, FDDI, ISDN, xDSL, frame relay, ATM, etc.

• Examples of the components of the network access layer– Drivers for software applications, modem cards, NICs, etc. – Modem protocol standards such as SLIP, PPP

• The role of the network access layer – Allows an IP packet to make a physical link to the network media

• Defines the procedures used to interface with the network hardware and access the transmission medium

• Maps IP addresses to physical hardware addresses • Encapsulates IP packets into frames • Defines the physical media connection based on the hardware type

and network interface



Network access layer




The OSI model and the TCP/IP model • Comparison of the OSI model and the TCP/IP model

– Similarities include: • Both have layers. • Both have application layers, though they include very different services. • Both have comparable transport and network layers. • Both models need to be known by networking professionals. • Both assume packets are switched

– Individual packets may take different paths to reach the same destination

– Differences include: • TCP/IP combines the presentation and session layer issues into its application layer. • TCP/IP combines the OSI data link and physical layers into the network access layer. • TCP/IP appears simpler because it has fewer layers. • TCP/IP protocols are the standards around which the Internet developed

– The TCP/IP model gains credibility– Networks are not usually built on the OSI protocol

» The OSI model is used as a guide

• Only TCP provides reliable delivery of packets while Layer 4 of OSI model always does



The OSI model and the TCP/IP model




Internet architecture • The limitation of the LAN

– Geographical distance– Scalability

• Requirements for internetworking– A network of networks– Scalability in size and distance– Flexibility for technology innovations– Adjustability to dynamic conditions on the network – Permit data communications to anyone, anywhere, at any time

• The concept of the Internet (IP network)– Uses the principle of network layer interconnection– Builds the functionality of the network in independent modules

• Allows intermediate networking devices to relay traffic without details about the LAN/WAN technologies and the applications

• Allows a diversity of LAN/WAN technologies at Layers 1 and 2 of the OSI model and a diversity of applications at Layers 5, 6, and 7



Internet architecture • Internetworking using the router

– Directly connected network

• All networks are directly connected to a router• A router knows about all networks• The router handles any path decisions required for the two networks

to communicate

LAN 1

LAN 2

LAN 3

LAN 4Router

W X

Y Z



Internet architecture – Internetworking using two or more routers

• Not all networks are directly connected to one another • Option 1

– A router keeps a list of all computers and all the paths to them – Not desirable when the networks grow large

• Option 2– A router keeps a list of all networks (or summary of networks), but

leaves the local delivery details to the local physical networks» Each router shares information about its connected network » The routers pass the information about the networks to other routers

X Y Z

LAN 2LAN 1 LAN 3

Router 1 Router 2



Internet architecture • User-transparency of the Internet

– The Internet acts like a transparent end-to-end network– The underlying structures can be extremely complex

• Over 90,000 core routes and 300,000,000 end users • Factors that ensures transparency

– All devices in the Internet follow certain hardware, software, and protocol standards







• Why the IP address is needed in the networking and how it is used• IPv4 address scheme and classification• The use of the reserved IP addresses• Efficient use of IP address space; private IP address, subnetting



Outlines9.2.1 IP addressing

9.2.2 Decimal and binary conversion

9.2.3 IPv4 addressing

9.2.4 Class A, B, C, D, and E IP addresses

9.2.5 Reserved IP addresses

9.2.6 Public and private IP addresses

9.2.7 Introduction to subnetting

9.2.8 IPv4 versus IPv6



IP addressing • Concept of IP address

– Each host in a TCP/IP network must have a unique identifier, or IP address

– IP address operates at Layer 3– It allows one computer to locate another computer on a network

• The concept of address grouping– An address is divided into the network address and host address




IP addressing • Why NOT MAC address? Why IP address?

MAC address IP address• Not systematic (Flat)

• Permanently assigned to the hardware

• Works well within a network

• In the switched network, too many ‘flooding of unknown destination’ occur

• Cannot be used to locate a network and a host

• Each switch must know the MAC address of all hosts in the entire network to communicate

• Difficult to use over the Internet

• Systematic (Hierarchical)

• Logically assigned to the networks and the hosts in them

• Can be used to locate a network and a host

• Each router knows the network address of all networks (or the summary of the networks) and the hosts in its own network



IP addressing

Network A

Network B

A router is a special computer:• Having multiple NIC ports• Multi-homed• Passes traffic between the

ports- It is called ‘routing’

Router


• Dual-homed computer– IP address is NOT assigned to

the computer, BUT assigned to the interface

– A dual-homed computer is attached to both networks



IP addressing • Notation of the IP address

– The length is 32-bit, separated by a period every octet– Usually written as four decimal numbers separated by periods

(Dotted decimal numbers)Copyrighted material is cleared



Decimal and binary conversion • It is important to remember the following relationships

• For more details on the conversion method, see module 1




IPv4 addressing


• The structure of the IP address– Consists of two part

• The network address– Identifies the network to which a host belongs

• The host address– Identifies the address of the host in that network

• Use of an IP address – Every packet has source and destination IP address– A router uses the destination IP address in the packet

• Determine the forwarding route from the source network to the destination

– Determine the destination network using the network address– Determine the destination host in that network using the host address



IPv4 addressing • Hierarchical structure of the IP address

– First octet of the IP address represents the highest hierarchy• There are 256 groups of IP addresses in this hierarchy• For each group, second octet of the IP address represents the next

highest hierarchy– There are 256 subgroups of IP addresses for a group of IP addresses– …

– Groups in the higher hierarchy represents the network addresses– Subgroups in the lower hierarchy represents the host addresses



Class A, B, C, D, and E IP addresses • Why class?

– Efficient use of IP address space is possible• Some networks are large, whereas some networks are small• Assign class A network to the large network and assign class

C network to the small network

• IP address classes

0.0.0~255.255.255

0.0~255.255

0~255

8 16 24 32

0 (1~126)

1 0 (128~191)

1 1 0 (192~223)

(240~255)

multicast addressmulticast address

reserved for future usereserved for future use

class A

class B

class C

class D

class E

0.0~255.255

0~255

1 1 1 1

1 1 1 0 (224~239)



Class A, B, C, D, and E IP addresses • Identifying IP address classes

• Number of networks and hosts in each IP address class

* 0.0.0.0 network and 127.0.0.0 network are reserved for the special uses





Class A, B, C, D, and E IP addresses

• IPv4 Address Space

class A

class B

class C

class Dclass E

0

128

192

224

240

(28/2 -2)nets×(224-2)hosts216/4 nets×(216-2)hosts

224/8 nets×(28-2)hosts



Class A, B, C, D, and E IP addresses




Reserved IP addresses• Network address

– All 0’s of host address bits• Identifies the network number itself

– Does not specify a specific host– All 0’s of 32 bits

1. Means ‘this host’ whose IP address is unknown to itself2. Means default network

• Broadcast address– All 1’s of host address bits

• Indicates all hosts in that network – All 1’s of 32 bits

• Indicates all hosts in this network when the host does not know its own IP address

• Local loopback address (127.x.x.x, normally 127.0.0.1)– Virtual interface of a device; NOT asigned to the physical interface– Normally used to test the TCP/IP capability of the host itself



Reserved IP addresses



Public and private IP addresses• Allocation of IP addresses

– Managed by IANA– Allocated to the regional Internet registry (RIR)

• Sub-allocated to the national Internet registry (NIR)– Sub-allocated to the ISP

» Users are assigned IP addresses by Internet service providers or Internet Registry

• Public IP address– Obtained from an ISP or a registry – Must be uniquely assigned throughout the Internet– Globally reachable network must use the public IP addresses

• Private IP address– For hosts in the network with no connection to the Internet – Can be non-unique throughout the world

• Should be unique within a network



Public and private IP addresses• Address allocation for private Internets (RFC 1918)

• Should not be routed outside the corporate LAN• Using private IP addresses with network address translation

– Networks using private IP addresses can be connected to the Internet via NAT

• Internetworking is possible for the hosts that use private IP addresses

– Typically operates at the border of a stub network• The border gateway router performs the NAT process

– Can be one of the solution for the exhaustion of the IP address

(1 Class A network)

(16 Class B networks)

(256 Class C networks)




Public and private IP addresses

NATInternal (private or local) network

External (public or global) network

NATprocess

SA 10.0.0.3

DA 128.23.2.2

SA 179.9.8.80

DA 128.23.2.2

NAT Table

SA 128.23.2.2

DA 179.9.8.80

SA 128.23.2.2

DA 10.0.0.3


Inside local IP address

Inside global IP address

Outside global IP address

10.0.0.3 179.9.8.80 128.23.2.2



Public and private IP addresses• Using private IP addresses for the point-to-point serial link

– Can be intermixed with public IP addresses– Conserves the number of addresses for internal connections




Public and private IP addresses

203.237.160.8

192.168.11.0

192.168.26.0

192.168.7.0

192.168.13.0 192.168.15.0210.181.186.4

203.249.39.111

203.237.166.10

203.249.39.0

203.237.166.0

210.181.186.0



Introduction to subnetting• Concept of subnetting (RFC 950)

– Dividing a classful network address space into smaller pieces• A class A, B, or C network can be subnetted into several subnets• Subnet mask is used to identify the subnets

– Enables efficient use of IP address spaces– Reduces the size of broadcast domain

• The router is needed to communicate between the subnets• Provides some level of security

131.108.0.0 (Class B) network131.108.1.0 subnetwork

131.108.2.0 subnetwork 131.108.3.0 subnetworkBroadcast domains




Introduction to subnetting• Engineering the network with the subnets

– Analyze current network size, future demands– Determine the size of networks and number of subnets

• Subnetting procedures– Borrows most significant bit(s) from the host field bits

• Maximum bits that can be borrowed = the number of host bits - 2– Designate them as the subnet bits– Address bits can be divided into

• Classful network address bits• Subnet address bit(s)• Host bits

8 16 24 32class A

class B

class C

New network address bits

Host address bits



Introduction to subnetting• Number of useable subnets

– 2subnet bits - 2• All-zeros subnet and all-ones subnet have been excluded

– To avoid confusion with the network’s own address and the broadcast address– Currently, they can be used if not the legacy network (RFC 1878)

• Number of useable hosts in a subnet– 2host bits – 2

• All-zeros host and all-ones host are the address of the subnet itself and the broadcast address, respectively

• Subnet mask– 32-bit – 1’s represent the portion of the network (including the subnet) address– 0’s represent the portion of the host in the subnet– Bitwise logical AND operation with the IP address yields the address of

the subnetwork– Can be represented as the subnet prefix number (number of 1’s)



Introduction to subnetting

Borrowed bits

Number of subnets (except all-zero subnet and all-one

subnet)Number of hosts per

subnetSubnet mask

(subnet prefix)

Class A Class B Class C Class A Class B Class C Class A Class B Class C

1 21 (21-2) 223-2 215-2 27-2255.128.0.0

(/9)255.255.128.0

(/17)255.255.255.128

(/25)

2 22 (22-2) 222-2 214-2 26-2255.192.0.0

(/10)255.255.192.0

(/18)255.255.255.192

(/26)

3 23 (23-2) 221-2 213-2 25-2255.224.0.0

(/11)255.255.224.0

(/19)255.255.255.224

(/27)

4 24 (24-2) 220-2 212-2 24-2255.240.0.0

(/12)255.255.240.0

(/20)255.255.255.240

(/28)

5 25 (25-2) 219-2 211-2 23-2255.248.0.0

(13)255.255.248.0

(/21)255.255.255.248

(/29)

6 26 (26-2) 218-2 210-2 22-2255.252.0.0

(/14)255.255.252.0

(/22)255.255.255.252

(/30)

7 27 (27-2) - 217-2 29-2 -255.254.0.0

(/15)255.255.254.0

(/23) -

8 28 (28-2) - 216-2 28-2 -255.255.0.0

(16)255.255.255.0

(/24) -

9 29 (29-2) - 215-2 27-2 -255.255.128.0

(/17)255.255.255.128

(/25) -

10 210 (210-2) - 214-2 26-2 -255.255.192.0

(/18)255.255.255.192

(/26) -

11 211 (211-2) - 213-2 25-2 -255.255.224.0

(/19)255.255.255.224

(/27) -

• Quick reference subnetting chart



Introduction to subnetting• Lab 9.2.7 IP Addressing Basics

• IP-Addressing Exercise

• Subnetting Exercise

Decimal number of last non-zero octet of the subnet mask (number of ones)

Increment of number of subnet

Subnet address increases by

Subnet addresses

128 (1) ×2 128 0, 128192 (2) ×4 64 0, 64, 128, 192224 (3) ×8 32 0, 32, 64, 96, 128, 160, 192, 224240 (4) ×16 16 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, …248 (5) ×32 8 0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, …252 (6) ×64 4 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, …254 (7) ×128 2 0, 2, 4, 6, 8, 10, 12, 16, 18, 20, 22, 24, 26, 28, …

5353

Introduction to subnetting• Subnetting chart

/25 /26 /27 /28 /29 /30Class CSubnetTable

.128 (100000000)2 subnets/128 hosts

.192(11000000)

2 subnets/62 hosts

.224(11100000)

6 subnets/30 hosts

.240(11110000)

14 subnets/14 hosts

.248(11111000)

30 subnets/6 hosts

.252(11111100)

62 subnets/2 hosts.0 .0.4 .4 (.5-.6).8 .8 .8 (.9-.10)

.12 (.9-.14) .12 (.13-.14)

.16 .16 .16 .16 (.17-.18)

.20 (.17-.22) .20 (.21-.22)

.24 (.17-.30) .24 .24 (.25-.26)

.28 (.25-.30) .28 (.29-.30)

.32 .32 .32 .32 .32 (.33-.34)

.36 (.33-.38) .36 (.37-.38)

.40 (.33-.46) .40 .40 (.41-.42)

.44 (.33-.62) (.41-.46) .44 (.45-.46)

.48 .48 .48 .48 (.49-.50)

.52 (.49-.54) .52 (.53-.54)

.56 (.49-.60) 0.56 .56 (.57-.58)

.60 (.1~.126) (.57-.62) .60 (.61-.62)

.64 .64 .64 .64 .64 .64 (.65-.66)

.68 (.65-.70) .68 (.69-.70)

.72 (.65-.78) .72 .72 (.73-.74)

.76 (.65-.94) (.73-.78) .76 (.77-.78)

.80 .80 .80 .80 (.81-.82)

.84 (.81-.86) .84 (.85-.86)

.88 (.81-.94) .88 .88 (.89-.90)

.92 (.65-.126) (.89-.94) .92 (.93-.94)

.96 .96 .96 .96 .96 (.97-.98).100 (.97-102) .100 (.101-.102).104 (.97-.110) .104 .104 (.105-.106).108 (.97-.126) (.105-.110) .108(.109-.110).112 .112 .112 .112 (.113-.114).116 (.113-.118) .116 (.117-.118).120 (.113-.126) .120 .120 (.121-.122).124 (.121-.126) .124 (.125-.126).128 .128 .128 .128 .128 .128 .128 (.129-.130).132 (.129-.134) .132 (.133-.134).136 (.129-.142) .136 .136 (.137-.138).140 (.129-.158) (.137-.142) .140 (.1417-.142).144 .144 .144 .144 (.145-.146).148 (.145-.150) .148 (.149-.150).152 (.145-.158) .152 .152 (.153-.154).156 (.129-.190) (.153-.158) .156 (.157-.158).160 .160 .160 .160 .160 (.161-.162).164 (.161-.166) .164 (.165-.166).168 (.161-.174) .168 .168 (.169-.170).172 (.161-.190) (.169-.174) .172 (.173-.174).176 .176 .176 .176 (.177-.178).180 (.177-.182) .180 (.181-.182).184 (.177-.190) .184 .184 (.185-.186).188 (.129~.254) (.185-.190) .188 (.189-.190).192 .192 .192 .192 .192 (.193-.194).196 (.193-.198) .196 (.197-.198).200 (.193-.206) '.200 .200 (.201-.202).204 (.193-.222) (.205-.206) .204 (.205-.206).208 .208 .208 .208 (.209-.210).212 (.209-.214) .212 (.213-.214).216 (.209-.222) .216 .216 (.217-.218).220 (.221-.222) .220 (.221-.222).224 .224 .224 .224 (.225-.226).228 (.225-.230) .228 (.229-.230).232 (.225-.238) .232 .232 (.233-.234).236 (.233-.238) .236 (.237-.238).240 .240 .240 (.241-.242).244 (.241-.246) .244 (.245-.246).248 .248 (.249-.250)

CCNA1 / 1st semester, 2007Network Information & Communication Program,




IPv4 versus IPv6

(27-2)×(224-2)214×(216-2)

221×(28-2)


• Allocation of IPv4 address space– Allocated by the class for the organizations

• Class A network for the large organizations• Class B network for the middle-size organizations• Class C network for the small organizations

– Inefficient and insufficient• With the class A, B networks,

too many IP addresses in a network but too few networks

• With the class C networks, toomany networks but too few IPaddresses in a network

– The size of the routing table getstoo large

• Introduced subnetting orCIDR with VLSM

– With the rapidly increasing demand for the IP addresses, they cannot be the perfect solutions



IPv4 versus IPv6 • Introduction of new IP addressing scheme

– IPv6 has been developed• Provides enough addresses (2128) for future communication needs

• Structure of the IPv6 address– 128bit (16 octets) address is separated by colon (:) every 16-bit

field – Each field is represented by 4-hexadecimal digits– Leading zeros in each field can be omitted







• How to assign IP information for a host- Statically- Dynamically; RARP, BOTP, DHCP

• How to get the MAC address of the destination host- When the destination is in the same network; ARP- When the destination is outside the same network; ARP, proxy ARP



Outlines9.3.1 Obtaining an Internet address

9.3.2 Static assignment of an IP address

9.3.3 RARP IP address assignment

9.3.4 BOOTP IP address assignment

9.3.5 DHCP IP address management

9.3.6 Problems in address resolution

9.3.7 Address Resolution Protocol (ARP)



Obtaining an Internet address


• Two methods to assign IP addresses1. Static addressing method

2. Dynamic addressing method• BOOTP, RARP, DHCP



Static assignment of an IP address • Works best on small, infrequently changing networks

– Suitable for network printers, application servers, and routers

• The system administrator manually assigns and tracks– Good recordkeeping is critical to prevent duplicate problems – Possible only when there are a small number of devices to track

• Parameters to be assigned– IP address– Subnet mask– Default gateway– DNS server– Etc.



RARP IP address assignment • RARP (Reverse Address Resolution Protocol)

– The client, such as diskless system, knows its own MAC address but not its own IP address

– The server keeps MAC address↔IP address mapping database• The database is maintained statically by the administrator

• Usually, the server is a router

• Associates the client’s MAC address with an IP addresses

– Procedures• The client host initiates a process called a RARP request

– RARP codes are in the ROM of the source device

– RARP requests are broadcast onto the LAN

• RARP server replies with the IP address for the client in the database

• The client binds its own MAC address to the received IP address



RARP IP address assignment • General structure of the RARP L2 frame (64 octets)

– Frame header• DA = 0xFFFFFFFFFFFF for RARP request (broadcast)• DA = Client’s MAC address for RARP reply (unicast)• Type = RARP request/reply (0x8035)

• General structure of the RARP packet (28 octets)

DA SA 0x8035 RARP (28Bytes) PAD ( ? Bytes) FCS

0x0001 (Ethernet) 0x0800 (IPv4)0x06 (Ethernet) 0x04 (IPv4) 0x0003/0x0004 (RARP request/reply)

Destination MAC address(Source MAC address for RARP request)

Source MAC addressSource IP addr. (undefined for RARP request)

Source IP address (continued)

Destination IP address (undefined for RARP request)



RARP IP address assignment • RARP procedures

0x0001 0x08000x06 0x04 0x0003

FE:ED:F9:23:44:EFundefined

FE:ED:F9:23:44:EFundefined

PAD FCS

FF:FF:FF:FF:FF:FF FE:ED:F9:23:44:EF 0x8035Transmit RARP request frameReceive RARP request frameDeencapsulate the framePass the packet up to the network layer

Packet is NOT for me! RARP request to me!

0x8035

RARP packet for me!

Keep the IP address

192.168.10.36

0x00030x0001 0x0800

0x06 0x04 0x0004FE:ED:F9:65:33:3A

192.168.10.98FE:ED:F9:23:44:EF

192.168.10.36PAD FCS

FE:ED:F9:23:44:EF FE:ED:F9:65:33:3A 0x8035

RARP reply for me!

Unicast RARP reply frameReceive RARP reply frame

192.168.10.36




BOOTP IP address assignment • The bootstrap protocol

– Operates in a client-server environment

– Uses UDP to carry messages

– Only requires a single packet exchange to obtain IP information

– Can get• The IP address, the address of a router, the address of a boot server,

bootfile name, and vendor-specific information – The client uses boot server information and bootfile name for subsequent

boot process

– Subsequent boot process typically uses TFTP for boot and receiving subnet mask, default gateway, DNS server, etc.

– Not designed to provide dynamic address assignment • The administrator must add hosts and maintain the BOOTP database



BOOTP IP address assignment • General structure of the BOOTP frame

– Frame header• DA (MAC) = 0xFFFFFFFFFFFF or specified BOOTP server for

request, or client’s MAC address for reply• Type = IPv4 (0x0800)

– IP header• Protocol = UDP• SA (IP) = all 0 (0.0.0.0; means “this host”) for request• DA (IP) = all 1 (255.255.255.255; means “broadcast to this network”)

or specified BOOTP server for request– ‘all 1’ also applies to BOOTP reply because the client still doesn’t know its

own IP address

– UDP header• SP & DP = 67 (for server) & 68 (for client)

DA SA 0x0800 Protocol SA DA FCSSP DP BOOTP (300Bytes)

L4 segment

L3 packet



BOOTP IP address assignment • General structure of the BOOTP message

Opcode/message type (Request=1/Reply=2)

H/W address type (Ethernet=1)

H/W address length (6)

Hop count

Transaction ID (randomly selected to identify a session; 4 Bytes)Number of seconds (From the client’s first try) Unused

Client IP Address (filled in by client; all 0s @ request)Your IP Address (filled by the BOOTP server)

Server IP Address (IP address of the server to be used for the subsequent boot process)Gateway IP Address (used in optional cross-gateway booting )

Client H/W Address (16 Bytes)Server Hostname (boot file server; 64 Bytes)

Boot filename (128 Bytes)Vender specific info (64 Bytes)



BOOTP IP address assignment • BOOTP request message

1 1 6 0221

2 UnusedClient IP address=0.0.0.0Your IP address=0.0.0.0

Server IP Address=0.0.0.0Gateway IP Address=0.0.0.0

Client H/W Address=FE:ED:F9:23:44:EFServer Hostname (specify boot file server to use; null if unspecified)

Boot filename (specify boot file name to use; null if unspecified)Vender specific info



BOOTP IP address assignment • BOOTP reply message

2 1 6 0221

2 UnusedClient IP address=0.0.0.0

Your IP address=192.168.10.36Server IP Address=192.168.10.97 (set to the IP addr. of the server to be used for the

subsequent bootstrap process)Gateway IP Address=0.0.0.0 (set to the IP address of the gateway if the server is not in the

same network; to identify the network to which the client belongs)Client H/W Address=FE:ED:F9:23:44:EF

Server Hostname=TFTP server nameBoot filename = Name of the boot file in the TFTP server

Vender specific info



BOOTP IP address assignment



DHCP IP address management • Dynamic host configuration protocol (DHCP)

– Successor to BOOTP

– Allows a host to obtain an IP address dynamically• No need to set up an individual profile for each device

• The DHCP server chooses an address from a pre-defined pool of IP addresses and leases it to that host

– Lease period can be pre-defined

• Offers mobility to the clients

• Efficient use of the IP address space is possible

– Only requires a single packet exchange to obtain IP information • Information from BOOTP + subnet mask, DNS server, WINS server,

and other TCP/IP configuration settings



DHCP IP address management • Comparison

BOOTP DHCPStatic MAC↔IP mapping from pre-defined table in the server

Dynamic mapping from a pool of IP addresses in the server

Permanent assignment Lease for a pre-defined periodOnly supports 4 basic parameters:

– IP address

– Gateway address

– Subnet mask

– DNS server address

Supports over 30 configuration parameters listed in RFC 1533

RFC 951 in 1985 RFC 2131 in 1997Uses UDP port 67 & 68 (client/server based)



DHCP IP address management • Overview of the operation

DiscoverOffer

255.255.255.255




DHCP IP address management • DHCP procedure overview

1. The client locates a DHCP server by broadcasting a DHCPDISCOVER• Sometimes the client may suggest the IP address it wants

2. The server determines whether it can service the request from its own DB • If it cannot, the server may forward the request on to another DHCP server• If it can, the DHCP server unicasts DHCPOFFER packet with lease information

3. The client selects one of the DHCPOFFERs from servers• Usually, the first received DHCPOFFER is selected• The client then broadcasts DHCPREQUEST to inform the selected offer

4. The selected server unicasts DHCPACK to the client• The client receives DHCPACK and begin using the assigned address

immediately • If the server send DHCPNACK, the client restarts the process

5. If the client detects that the address is already in use on the local segment, it will send a DHCPDECLINE message and the process restarts

6. If the client no longer needs the IP address, the client sends a DHCPRELEASE message to the server



DHCP IP address management • General structure of the DHCP frame

– Frame header• DA (MAC) = 0xFFFFFFFFFFFF for DHCP discover & request, client’s

MAC address for offer & acknowledge• Type = IPv4 (0x0800)

– IP header• Protocol = UDP• SA (IP) = all 0 (0.0.0.0) for request• DA (IP) = all 1 (255.255.255.255) for DHCP discover & request

– Unselected server must be notified too at the request phase– In many cases, ‘all 1’ also applies to DHCP offer & DHCP acknowledge

because the client still doesn’t know its own IP address» This happens when the client has set flags=0x8000 at the query and request

– UDP header• SP & DP = 67 (for server) & 68 (for client)

DA SA 0x0800 Protocol SA DA FCSSP DP DHCP (548Bytes)



DHCP IP address management • General structure of the DHCP message

– Almost the same as that of the BOOTP• Same field length unless specified

Opcode/message type (Request=1/Reply=2)

H/W address type (Ethernet=1)

H/W address length (6)

Hop count

Transaction ID (randomly selected to identify a session)Number of seconds Flags

Client IP Address (filled in by client; all 0s @ discover)Your IP Address (filled by the BOOTP server @ offer)

Server IP AddressGateway IP Address (relay agent; set by the router to gateway address if DHCP server was

outside the client’s network)Client H/W Address

Server Hostname (boot file server)Boot filename

Options (312 Bytes or more)



DHCP IP address management • DHCP discover message

1 1 6 012

2 0x8000(broadcast to client)/0x0000(unicast)0.0.0.00.0.0.00.0.0.00.0.0.0

AA:EC:F9:23:44:19NullNull

Options (312 Bytes or more)



DHCP IP address management • DHCP offer message

2 1 6 012

2 0x8000(broadcast to client)/0x0000(unicast)0.0.0.0

192.168.10.35192.168.10.98 (or IP address of the next bootstrap server)

0.0.0.0 (set to gateway address if DHCP server was outside the client’s network)AA:EC:F9:23:44:19

NullNull

Server identifier=192.168.10.98



DHCP IP address management • DHCP request message

1 1 6 012

2 0x8000(broadcast to client)/0x0000(unicast)0.0.0.00.0.0.00.0.0.00.0.0.0

AA:EC:F9:23:44:19NullNull

Requested IP address=192.168.10.35 Server identifier=192.168.10.98



DHCP IP address management • DHCP acknowledge message

2 1 6 012

2 0x8000(broadcast to client)/0x0000(unicast)0.0.0.0

192.168.10.35192.168.10.98 (or IP address of next bootstrap server)

0.0.0.0 (set to gateway address if DHCP server was outside the client’s network)AA:EC:F9:23:44:19

NullNull

Server identifier=192.168.10.98



DHCP IP address management



DHCP IP address management• DHCP procedure example

1. Setup in the OS



DHCP IP address management

DHCP clients203.249.39.26

2.Network configuration

203.237.160.1 DHCP server

Routers(relay agent)

218.145.241.1



DHCP IP address management3. DHCP

discover



DHCP data



frame



4. DHCP offer



DHCP data



frame



5. DHCP request



DHCP data



frame



6. DHCP acknowledge



DHCP data



frame



7. Results



Problems in address resolution • Learning the MAC address↔IP address mapping

– Within a LAN segment• In the Ethernet, source MAC address and source IP address in a frame

is monitored to learn the source host’s MAC address and IP addressby all hosts in the segment

– Monitor broadcast traffic and unicast traffic destined to itself

– It does NOT ALWAYS work

• How do hosts know the MAC address and the IP address of a host that has not sent a packet yet?

– ARP solves this problem



Problems in address resolution – Across the LAN segments

• MAC address is meaningful only within a LAN– The switch switches a Layer 2 frame transparently based on the

destination MAC address of the frame

– The router switches a Layer 3 packet transparently based on the IP address of the packet

– The router is a special computer with multiple NICs

– Each NIC has its own MAC address for the communication

– To communicate with the host outside a LAN, it is necessary to communicate with the gateway (router) to that network first

– In that case, the MAC address of the NIC in the router is used for the communication

» Proxy ARP or ARP to the default gateway can locate that MAC address

• Learning the MAC address of the destination outside a LAN is meaningless



Problems in address resolution



Address Resolution Protocol (ARP) • ARP table

– MAC address↔IP address mapping table for other hosts that are connected to the same LAN

• Used to identify the MAC address of the destination, given the IP address of the destination

– Stored in RAM memory – Usually maintained automatically by the OS



Address Resolution Protocol (ARP)• Building the ARP table for the hosts within a LAN segment

1. By monitoring the traffic within the segment• Monitor each frame and record its source IP address and MAC

address into the ARP table

• It does not always work

2. By broadcasting the ARP request to the network• ARP request includes the destination IP address whose MAC

address is wanted

• Destination host unicasts ARP reply with its own MAC address

• Receive the ARP reply and build the ARP table from it



Address Resolution Protocol (ARP)• Learning by monitoring at host 176.10.16.1

ARP cache timeout




Address Resolution Protocol (ARP) • ARP process



Address Resolution Protocol (ARP)




Address Resolution Protocol (ARP)• Sending a packet from 176.10.16.1 to 176.10.16.4

– Assume that 176.10.16.1 doesn’t know the MAC address of 176.10.16.4

1 starts ARP request

4 recognizes ARP request4 receives ARP request

4 starts ARP reply1 receives ARP reply1 sends a packet to 44 receives the packet Copyrighted material is cleared



Address Resolution Protocol (ARP)• Example of an ARP for ping

– Pinging from 203.237.160.84 to 203.237.160.81



Address Resolution Protocol (ARP)– Packet flow overview



Address Resolution Protocol (ARP)– 203.237.160.84 looks for the MAC address of 203.237.160.81



Address Resolution Protocol (ARP)– 203.237.160.81 replies its MAC address to 203.237.160.81



– 1st pingrequest



– 1st pingreply



– 4th pingrequest



– 4th pingreply



Address Resolution Protocol (ARP)• Data communication in the IP network

1. Anyway, a node has a packet to send• In the router, it may be received from a host or from another router

• In a host, it may be received from the upper layer of the host

• It has a source IP address– It is the sending end’s IP address

• It has a destination IP address– It is the receiving end’s IP address

2. A node has its own IP address and the subnet mask• Represents the network address it belongs + node address in the

network



Address Resolution Protocol (ARP)3. Determine the best path toward the destination (routing at L3)

• Determine the destination network– The IP address of the node (source) and destination are logical ANDed

with the subnet mask, respectively

– If the two results are the same, the destination network is the same as the network to which the node belongs

– If they are different, the destination network is not the same• Determine the best output port to the destination network

– A routing table is used to determine the best path» The routing table has a list of networks and the cost of each port through

which a packet travels to the destination network» Select the port that has the minimum cost to the destination network

– If the destination network is directly connected to the node, the selected port is directly connected to that network

– If not, the selected port is connected to the gateway to the destination network

» Normally, the gateway is a router’s port



Address Resolution Protocol (ARP)4. Prepare a frame to send to the selected output port (Framing at

L2)• Now, the packet is to be encapsulated into a frame

– The source and the destination MAC address are needed• The source MAC address is that of the output port (NIC)• There are two cases for the destination MAC address

– If the destination network is directly connected to the output port,» The destination MAC address is that of the destination device’s NIC» It can be determined by the normal ARP broadcast to that network» The frame is sent directly to the destination

– If not, the frame must be routed by the gateway» The host send the packet to the default gateway to have it routed» The destination MAC address is that of the receiving port of the gateway» It can be determined by one of the following methods



Address Resolution Protocol (ARP)• ARP for communication with outside the LAN segment

– The node must communicate with the router (gateway) first– Determining the MAC address of the gateway

1. If the IP address of the default gateway is set in the node, broadcast ARP request for the IP address of the default gateway

2. If the IP address of the default gateway is NOT set, broadcast ARP request for IP address of the destination host

– Some legacy systems do not have the means to set the default gateway

– If the gateway (router) is set to work as a proxy ARP (default for the Cisco router), it replies the ARP broadcast with the MAC address of its own incoming port

• Both of the results are the same

– The source node uses the MAC address of the default gateway as the destination MAC address

• Destination IP address is unchanged



Router Router




• Proxy ARP

• Default gateway




What do these results mean?



Address Resolution Protocol (ARP) • Lab 9.3.7 Workstation ARP

1. Find the IP address of the host in the same network2. Prepare Ethereal or Protocol Inspector for capturing ARP packet

– Apply capture filter for the ARP packet

3. Display current MAC address table by typing arp –a in the command window4. Clear MAC address table by typing arp –d in the command window and

display the MAC address table again5. Start capture at the Ethereal or Protocol Inspector 6. Ping to the host in the same network7. Ping to the host outside the network (such as www.yahoo.com) 8. Stop capture at the Ethereal or Protocol Inspector 9. Display the ARP table10.Analyze the sender, receiver, replier, and the contents of ARP packets for both

case (steps 6 & 7) and explain the results– Caution: In the college network, ping to the outside the campus network is

impossible because of the FIREWALL



Summary• Students should understand the following main points:

– Why the Internet was developed and how TCP/IP fits the design of the Internet– The four layers of the TCP/IP model– The functions of each layer of the TCP/IP model– The OSI model compared to the TCP/IP model– IP addressing gives each device on the Internet a unique identifier– IP address classes are logical divisions of the address space used to meet the needs of

various size networks– Subnetting is used to divide a network into smaller networks– Reserved addresses fulfill a special role in IP addressing and cannot be used for any other

purpose– Private addresses cannot be routed on the public Internet– The function of a subnet mask is to map the parts of an IP address that are the network and

the host– Someday IPV4 will be completely obsolete and IPV6 will be the commonly used version– A computer must have an IP address to communicate on the Internet– An IP address may be configured statically or dynamically– A dynamic IP address may be allocated using RARP, BOOTP, or DHCP– DHCP supplies more information to a client than BOOTP– DHCP allows computers to be mobile allowing a connection to many different networks– ARP and Proxy ARP can be used to solve address resolution problems

ccna 1 v3.11 module 9ocw.dongyang.ac.kr/cms_ocw/network/435/note/5_10.pdf · ccna1 / 1st semester,...

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