TCP/IP & INTERNET Unit 2 Department Of Computer Science & Engineeing

Syllabus Internet Addresses: IP address classes subnet mask CIDR,ARP,RARP Internet Protocol Routing IP Datagram’s ICMP and IGMP.

Learning Objective Understand IPv4 addresses and classes Identify the class of an IP address Find the network address given an IP address Understand masks and how to use them Understand the different types of delivery and the connection Understand forwarding techniques in classful addressing Understand forwarding techniques in classless addressing

Learning Objective Continue… Understand the need for ARP Understand the cases in which ARP is used Understand the components and interactions in an ARP package Understand the need for RARP Understand the format and fields of a datagram Understand the need for fragmentation and the fields involved Understand the options available in an IP datagram Know the types of error reporting messages Know the types of query messages Be able to calculate the ICMP checksum Know how to use the ping and traceroute commands Know the purpose of IGMP Know the types of IGMP messages Understand how a member joins a group and leaves a group Understand membership monitoring

Introduction The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet is called the Internet address or IP address. An IP address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet. IP addresses are unique. They are unique in the sense that each address defines one, and only one, connection to the Internet. Two devices on the Internet can never have the same address.The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet is called the Internet address or IP address. An IP address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet. IP addresses are unique. They are unique in the sense that each address defines one, and only one, connection to the Internet. Two devices on the Internet can never have the same address.

An IP address is a 32-bit address. The IP addresses are unique. The address space of IPv4 is 2 32 or 4,294,967,296.

Dotted Decimal Figure : Dotted-decimal notation

CLASSFUL ADDRESSING IP addresses, when started a few decades ago, used the concept of classes. This architecture is called classful addressing. In the mid-1990s, a new architecture, called classless addressing, was introduced and will eventually supersede the original architecture. However, part of the Internet is still using classful addressing, but the migration is very fast.IP addresses, when started a few decades ago, used the concept of classes. This architecture is called classful addressing. In the mid-1990s, a new architecture, called classless addressing, was introduced and will eventually supersede the original architecture. However, part of the Internet is still using classful addressing, but the migration is very fast.

Topics in Classful Addressing Recognizing ClassesRecognizing Classes Netid and HostidNetid and Hostid Classes and BlocksClasses and Blocks Network AddressesNetwork Addresses Sufficient InformationSufficient Information MaskMask CIDR NotationCIDR Notation Address DepletionAddress Depletion

Occupation of the address space

Addresses per class

Finding the class in binary notation

Finding the address class

Finding the class in decimal notation

Netid and hostid

Note Millions of class A addresses are wasted. Many class B addresses are wasted. The number of addresses in class C is smaller than the needs of most organizations. Class D addresses are used for multicasting; there is only one block in this class. Class E addresses are reserved for future purposes; most of the block is wasted.

Blocks in Class A

Blocks in class B

Blocks in class C

Note: In classful addressing, the network address (the first address in the block) is the one that is assigned to the organization. The range of addresses can automatically be inferred from the network address.

Masking Concept

Figure : AND operation

Default Mask

The network address is the beginning address of each block. It can be found by applying the default mask to any of the addresses in the block (including itself). It retains the netid of the block and sets the hostid to zero. Note that we must not apply the default mask of one class to an address belonging to another class.

Special IP Address

Figure : Default mask and subnet mask

CIDR In CIDR notation, the block granted is defined by the first address and the prefix length.

Table :Prefix lengths

Delivery The network layer supervises delivery, the handling of the packets by the underlying physical networks. Two important concepts are the type of connection and direct versus indirect delivery.The network layer supervises delivery, the handling of the packets by the underlying physical networks. Two important concepts are the type of connection and direct versus indirect delivery.

Figure : Direct delivery

Figure : Indirect delivery

Forwarding Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table..Forwarding means to place the packet in its route to its destination. Forwarding requires a host or a router to have a routing table..

Next-hop method

Figure :Network-specific method

Figure : Host-specific routing

Figure : Default routing

Figure : Simplified forwarding module in classful address without subnetting

Figure : Simplified forwarding module in classful address with subnetting

Note In classful addressing we can have a routing table with three columns; in classless addressing, we need at least four columns.

Figure :Simplified forwarding module in classless address

Routing Routing deals with the issues of creating and maintaining routing tables.Routing deals with the issues of creating and maintaining routing tables. Figure : Common fields in a routing table

ARP & RARP ARP associates an IP address with its physical address. On a typical physical network, such as a LAN, each device on a link is identified by a physical or station address that is usually imprinted on the NIC. ARP & RARP ARP associates an IP address with its physical address. On a typical physical network, such as a LAN, each device on a link is identified by a physical or station address that is usually imprinted on the NIC. Figure : ARP and RARP

Figure : ARP operation

Figure : ARP packet

Figure : Encapsulation of ARP packet

Figure : Four cases using ARP

RARP RARP finds the logical address for a machine that only knows its physical address.RARP finds the logical address for a machine that only knows its physical address. The RARP request packets are broadcast; the RARP reply packets are unicast.

Figure : RARP operation

Figure : RARP packet

Figure: Encapsulation of RARP packet

IP A packet in the IP layer is called a datagram, a variable-length packet consisting of two parts: header and data. The header is 20 to 60 bytes in length and contains information essential to routing and delivery.A packet in the IP layer is called a datagram, a variable-length packet consisting of two parts: header and data. The header is 20 to 60 bytes in length and contains information essential to routing and delivery.

Figure : IP datagram

The precedence subfield was designed, but never used in version 4. Figure: Service type or differentiated services

Table : Types of service

Table : Default types of service

Table : Values for codepoints The total length field defines the total length of the datagram including the header.

Figure : Multiplexing

Fragmentation The format and size of a frame depend on the protocol used by the physical network. A datagram may have to be fragmented to fit the protocol regulations.The format and size of a frame depend on the protocol used by the physical network. A datagram may have to be fragmented to fit the protocol regulations.

Figure : MTU Figure : Flags field

Option The header of the IP datagram is made of two parts: a fixed part and a variable part. The variable part comprises the options that can be a maximum of 40 bytes.The header of the IP datagram is made of two parts: a fixed part and a variable part. The variable part comprises the options that can be a maximum of 40 bytes.

Figure : Option format

Figure : Categories of options

Checksum The error detection method used by most TCP/IP protocols is called the checksum. The checksum protects against the corruption that may occur during the transmission of a packet. It is redundant information added to the packet.The error detection method used by most TCP/IP protocols is called the checksum. The checksum protects against the corruption that may occur during the transmission of a packet. It is redundant information added to the packet.

Checksum At Sender Side To create the checksum the sender does the following: ❏ The packet is divided into k sections, each of n bits. ❏ All sections are added together using 1’s complement arithmetic. ❏ The final result is complemented to make the checksum.

Figure : Checksum concept

ICMP ICMP messages are divided into error- reporting messages and query messages. The error-reporting messages report problems that a router or a host (destination) may encounter. The query messages get specific information from a router or another host.ICMP messages are divided into error- reporting messages and query messages. The error-reporting messages report problems that a router or a host (destination) may encounter. The query messages get specific information from a router or another host.

Figure : ICMP messages

Table : ICMP messages

An ICMP message has an 8-byte header and a variable-size data section. Although the general format of the header is different for each message type, the first 4 bytes are common to all. Figure : General format of ICMP messages

IP, as an unreliable protocol, is not concerned with error checking and error control. ICMP was designed, in part, to compensate for this shortcoming. ICMP does not correct errors, it simply reports them ICMP always reports error messages to the original source.

ICMP can also diagnose some network problems through the query messages, a group of four different pairs of messages. In this type of ICMP message, a node sends a message that is answered in a specific format by the destination node.

Debugging Tools We introduce two tools that use ICMP for debugging: ping and traceroute.We introduce two tools that use ICMP for debugging: ping and traceroute.

Figure : The traceroute program operation

IGMP IGMP is a protocol that manages group membership. The IGMP protocol gives the multicast routers information about the membership status of hosts (routers) connected to the network..IGMP is a protocol that manages group membership. The IGMP protocol gives the multicast routers information about the membership status of hosts (routers) connected to the network.. IGMP is a group management protocol. It helps a multicast router create and update a list of loyal members related to each router interface.

Types of Messages: IGMP has three types of messages: the query, the membership report, and the leave report. There are two types of query messages, general and special.IGMP has three types of messages: the query, the membership report, and the leave report. There are two types of query messages, general and special.

Figure : IGMP message types

Figure : IGMP message format

Table : IGMP type field

IGMP Operation A multicast router connected to a network has a list of multicast addresses of the groups with at least one loyal member in that network. For each group, there is one router that has the duty of distributing the multicast packets destined for that group.A multicast router connected to a network has a list of multicast addresses of the groups with at least one loyal member in that network. For each group, there is one router that has the duty of distributing the multicast packets destined for that group.

Figure : IGMP operation

Figure : Membership report In IGMP, a membership report is sent twice, one after the other.

Figure : Leave report

Figure : General query message

Summary The IP address is of 32 bits and universally unique. The IP address consist of net id and host id Five classes of IP address: A, B. C D & E Delivery, forwarding & routing is studied Structure of router is studied, Physical address identifies a host or router at the physical level ARP request is broadcast &reply is unicast IP is unreliable connectionless protocol responsible for source to destination delivery Fragmentation is the division of datagram into smaller units to accommodate the MTU of data link protocol. Error detection method is called checksum ICMP & IGMP is studied.

References TCP/IP Protocol suite, Behrouz A. Forouzan, Third Edition, TMH. Internetworking and TCP/IP: Principles, Protocols and Architectures, Douglas Comer, Pearson Education Computer Network by William Stallings