CN Unit IV - Internetworking

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Network Layer design issues, IPV4, IPV6, ARP, RARP, ICMP(V4&V6)

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Unit IV: Internetworking Reference: Kurose, Ross “Computer Networking-a top down approach featuring the internet” and Andrew Tanenbaum “Computer Network” Slides p repared by: Mr. Vaibhav Dabhade for TE Computer Engineering

Network Layer Design Isues:

Network Layer Design Isues Store-and-Forward Packet Switching Services Provided to the Transport Layer Implementation of Connectionless Service Implementation of Connection-Oriented Service Comparison of Virtual-Circuit and Datagram Subnets

Store-and-Forward Packet Switching:

Store-and-Forward Packet Switching The environment of the network layer protocols. fig 5-1

Services Provided to the Transport Layer :

Services Provided to the Transport Layer The network layer services have been designed with the following goals in mind. The services should be independent of the router technology. The transport layer should be shielded from the number, type, and topology of the routers present. The network addresses made available to the transport layer should use a uniform numbering plan, even across LANs and WANs. Internet community : argues that the routers' job is moving packets around and nothing else  Conclusion : Connection less Services Telephone companies : argues that the subnet should provide a reliable, connection-oriented service.

Implementation of Connectionless Service:

Implementation of Connectionless Service Routing within a diagram subnet.

Implementation of Connection-Oriented Service:

Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet.

Comparison of Virtual-Circuit and Datagram Subnets:

Comparison of Virtual-Circuit and Datagram Subnets 5-4

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IP

The IP Protocol:

The IP Protocol

IP Addresses:

IP Addresses IP address formats.

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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 IPv4 address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet, An IPv6 address is a 128-bit address An IP address is the address of the interface. Subnetting: Short-term Solution.

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An IPv4 address is 32 bits long. Note The IPv4 addresses are unique and universal. Note

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The address space of IPv4 is 2 32 or 4,294,967,296. Note

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Dotted-decimal notation

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Change the following IPv4 addresses from binary notation to dotted-decimal notation. a. 10000001 00001011 00001011 11101111 b. 11000001 10000011 00011011 11111111 Solution We replace each group of 8 bits with its equivalent decimal number and add dots for separation: a. 129.11.11.239 b. 193.131.27.255

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Change the following IPv4 addresses from dotted-decimal notation to binary notation. a. 111.56.45.78 b. 221.34.7.82 c. 241.8.56.12 Solution We replace each decimal number with its binary equivalent: a. 01101111 00111000 00101101 01001110 b. 11011101 00100010 00000111 01010010 c. 11110001 00001000 00111000 00001100

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Find the error, if any, in the following IPv4 addresses: a. 111.56.045.78 b. 221.34.7.8.20 c. 75.45.301.14 d. 11100010.23.14.67 Solution a. There should be no leading zeroes (045). b. We may not have more than 4 bytes in an IPv4 address. c. Each byte should be less than or equal to 255. d. A mixture of binary notation and dotted-decimal notation.

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A 32-bit IPv4 address was logically subdivided into the network number field & rest field, This format was sufficient at a time when only a few large networks existed, IP addresses, when started a few decades ago, used the concept of classes, This architecture is called classful addressing, The method divides the address space for Internet Protocol Version 4 (IPv4) into five address classes.

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Find the class of each address: a. 00000001 00001011 00001011 11101111 b. 11000001 10000011 00011011 11111111 c. 10100111 11011011 10001011 01101111 d. 11110011 10011011 11111011 00001111 Solution See the procedure in Figure 5.7. a. The first bit is 0. This is a class A address. b. The first 2 bits are 1; the third bit is 0. This is a class C address. c. The first bit is 1; the second bit is 0. This is a class B address. d. The first 4 bits are 1s. This is a class E address.

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Find the class of each address: a. 227.12.14.87 b. 193.14.56.22 c. 14.23.120.8 d. 252.5.15.111 Solution a. The first byte is 227 (between 224 and 239); the class is D. b. The first byte is 193 (between 192 and 223); the class is C. c. The first byte is 14 (between 0 and 127); the class is A. d. The first byte is 252 (between 240 and 255); the class is E.

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Netid and hostid

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Blocks in Class A

Address Resolution Protocol (ARP):

Address Resolution Protocol (ARP)

Overview:

Overview

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Figure 7.1 ARP and RARP

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ARP 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. Address resolution provides a mapping between the two different forms of address. 32-bit Internet address 48-bit Ethernet address

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Figure 7.3 ARP operation

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Figure 7.4 ARP packet Hardware Type - Ethernet is type 1 Protocol Type- IPv4=x0800 Hardware Length:length of Ethernet Address (6) Protocol Length:length of IPv4 address (4)

Operation of ARP (An Example):

Operation of ARP (An Example) The application calls the function “gethostbyname” to convert the hostname into its 32-bits IP address. The FTP client asks its TCP to establish a connection with that IP address. TCP sends a connection request segment to the remote host by sending an IP datagram to its IP address.

Operation of ARP (An Example):

Operation of ARP (An Example) If the destination host is on a locally attached network, the IP datagram can be sent directly to that host. If the destination host is on a remote network, the IP routing function determines the Internet address of a locally attached next-hop router to send the IP datagram to.

Operation of ARP (An Example):

Operation of ARP (An Example) Assuming an Ethernet, the sending host must convert the 32-bit IP address into a 48-bit Ethernet address. ARP is intended for broadcast networks where many hosts or routers are connected to a single network. ARP sends an Ethernet frame called an ARP request to every host on the network. This is called broadcast.

Operation of ARP (An Example):

Operation of ARP (An Example) The destination host’s ARP layer receives this broadcast recognizes that the sender is asking for its hardware address, and replies with an ARP reply. The ARP reply is received and the IP datagram that forced the ARP request-reply to be exchanged can now be sent. The IP datagram is sent to the destination host.

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Figure 7.6 Four cases using ARP

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Reverse Address Resolution Protocol RARP finds the logical address for a machine that only knows its physical address. This if often encountered on thin-client workstations. No disk, so when machine is booted, it needs to know its IP address. RARP requests are broadcast, RARP replies are unicast. If a thin-client workstation needs to know its IP address, it probably also needs to know its subnet mask, router address, DNS address, etc. So we need something more than RARP. BOOTP, and now DHCP have replaced RARP.

ARP and RARP:

ARP and RARP Note: The Internet is based on IP addresses Protocols (Ethernet, FDDI, ATM) may have different (MAC) addresses The ARP and RARP protocols perform the translation between IP addresses and MAC layer addresses

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RARP RARP finds the logical address for a machine that only knows its physical address. The topics discussed in this section include: Packet Format Encapsulation RARP Server

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RARP operation

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RARP packet

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Encapsulation of RARP packet

RARP Server Design:

RARP Server Design RARP Servers as User Processes The complication with an RARP server is that the server normally provides the mapping from a hardware address to an IP address for many hosts. RARP requests are transmitted as Ethernet frames with a specific Ethernet frame type field.

RARP Server Design:

RARP Server Design Multiple RARP Servers per Network RARP requests are sent as hardware-level broadcasts. As the number of servers increases, the network traffic increase, since every server sends an RARP reply for every RARP request. The diskless system that sent the RARP request normally uses the first RARP reply that it receives.

Summary:

Summary RARP is used by many diskless systems to obtain their IP address when bootstrapped. The RARP packet format is nearly identical to the ARP packet. Problems with RARP include its use of a link-layer broadcast, preventing most routers from forwarding an RARP request, and the minimal information returned. While the RARP concept is simple, the implementation of an RARP server is system dependent.

Internet Control Message Protocol (ICMP):

Internet Control Message Protocol (ICMP)

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21-2 ICMP The IP protocol has no error-reporting or error-correcting mechanism. The IP protocol also lacks a mechanism for host and management queries. The Internet Control Message Protocol (ICMP) has been designed to compensate for the above two deficiencies. It is a companion to the IP protocol.

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Figure 21.8 General format of ICMP messages

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ICMP type code description 0 0 echo reply (to ping) 3 0 destination network unreachable 3 1 destination host unreachable 3 2 destination protocol unreachable 3 3 destination port unreachable 3 6 destination network unknown 3 7 destination host unknown 4 0 source quench (congestion control) 8 0 echo request 9 0 router advertisement 10 0 router discovery 11 0 TTL expired 12 0 IP header bad Selected ICMP messages

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ICMP always reports error messages to the original source. Note

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Figure 21.9 Error-reporting messages

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Important points about ICMP error messages : ❏ No ICMP error message will be generated in response to a datagram carrying an ICMP error message. ❏ No ICMP error message will be generated for a fragmented datagram that is not the first fragment. ❏ No ICMP error message will be generated for a datagram having a multicast address.

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Figure 21.11 Redirection concept

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Figure 21.12 Query messages

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Figure 21.13 Encapsulation of ICMP query messages

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Example 21.3 (continued)

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Figure 21.15 The traceroute program operation

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21. 57 21-4 ICMPv6 We discussed IPv6 in Chapter 20. Another protocol that has been modified in version 6 of the TCP/IP protocol suite is ICMP (ICMPv6). This new version follows the same strategy and purposes of version 4. Error Reporting Query Topics discussed in this section:

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21. 58 Figure 21.23 Comparison of network layers in version 4 and version 6

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21. 59 Table 21.3 Comparison of error-reporting messages in ICMPv4 and ICMPv6

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21. 60 Table 21.4 Comparison of query messages in ICMPv4 and ICMPv6

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