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Computer Networks Unit III Network layer (2012 pattern) By Prof. B.A.Khivsara Assistant Prof. Department of Computer Engg. SNJB’s KBJ COE, Chandwad Introduction1-1.

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Presentation on theme: "Computer Networks Unit III Network layer (2012 pattern) By Prof. B.A.Khivsara Assistant Prof. Department of Computer Engg. SNJB’s KBJ COE, Chandwad Introduction1-1."— Presentation transcript:

1 Computer Networks Unit III Network layer (2012 pattern) By Prof. B.A.Khivsara Assistant Prof. Department of Computer Engg. SNJB’s KBJ COE, Chandwad Introduction1-1

2 Introduction1-2 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

3 Introduction1-3 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

4 20.4 Basics of IPv4 The Internet Protocol version 4 (IPv4) is the delivery mechanism used by the TCP/IP protocols. Datagram Classes Options Topics discussed in this section:

5 Position of IPv4 in TCP/IP protocol suite

6 IPv4 datagram format (IPV4 Header)

7  Version: IP Version ◦ 4 for IPv4 ◦ 6 for IPv6  HLen: Header Length ◦ 32-bit words (typically 5)  TOS: Type of Service ◦ Priority information  Identifier, flags, fragment offset  used primarily for fragmentation  Time to live ◦ Must be decremented at each router ◦ Packets with TTL=0 are thrown away ◦ Ensure packets exit the network  Protocol ◦ Demultiplexing to higher layer protocols ◦ TCP = 6, ICMP = 1, UDP = 17…  Header checksum ◦ Ensures some degree of header integrity ◦ Relatively weak – only 16 bits  Options ◦ E.g. Source routing, record route, etc. ◦ Performance issues at routers  Poorly supported or not at all  Source Address ◦ 32-bit IP address of sender  Destination Address ◦ 32-bit IP address of destination

8 20.8 Service type field in IPV4

9 Protocol values

10 5-54

11 11 IPv4 Addressing- Introduction An IP address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet. 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.

12 12 An IP address is a 32-bit address. Note:

13 13 The IP addresses are unique. Note:

14 14 The address space of IPv4 is 2 32 or 4,294,967,296. Note:

15 15 Dotted-decimal and Binary equivalent notation

16 16 Change the following IP addresses from binary notation to dotted-decimal notation. a b c d Example 1 Solution We replace each group of 8 bits with its equivalent decimal number and add dots for separation: a b c d

17 17 Change the following IP addresses from dotted-decimal notation to binary notation. a b c d Example 2 Solution We replace each decimal number with its binary equivalent: a b c d

18

19 19 Finding the class in binary notation

20 20 Find the class of each address: a b c d Example Solution 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 0; the second bit is 1. This is a class B address. d. The first 4 bits are 1s. This is a class E address..

21 21 Finding the class in decimal notation

22 22 Find the class of each address: a b c d e Example 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. e. The first byte is 134 (between 128 and 191); the class is B.

23 23 Netid and hostid

24 24 Given the network address , find the class, the block, and the range of the addresses. Example Solution The class is A because the first byte is between 0 and 127. The block has a netid of 17. The addresses range from to

25 25 Given the network address , find the class, the block, and the range of the addresses. Example Solution The class is B because the first byte is between 128 and 191. The block has a netid of The addresses range from to

26 26 Given the network address , find the class, the block, and the range of the addresses. Example Solution The class is C because the first byte is between 192 and 223. The block has a netid of The addresses range from to

27 TCP/IP Protocol Suite27 Masking concept

28 TCP/IP Protocol Suite28

29 TCP/IP Protocol Suite29 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:

30 TCP/IP Protocol Suite30 Given the address , find the beginning address (network address). Example Solution The default mask is , which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is

31 TCP/IP Protocol Suite31 Given the address , find the beginning address (network address). Example Solution The default mask is , which means that the first 2 bytes are preserved and the other 2 bytes are set to 0s. The network address is

32 TCP/IP Protocol Suite32 Given the address , find the beginning address (network address). Example Solution The default mask is , which means that the first 3 bytes are preserved and the last byte is set to 0. The network address is

33 .

34 TCP/IP Protocol Suite34 IPv4 Addressing- Subnetting The problems associated with classful addressing is that the network addresses available for assignment to organizations are close to depletion. This is coupled with the ever-increasing demand for addresses from organizations that want connection to the Internet. In this section we briefly discuss two solutions: subnetting and supernetting.

35 TCP/IP Protocol Suite35 IP addresses are designed with two levels of hierarchy. Note:

36 TCP/IP Protocol Suite36 A network with two levels of hierarchy (not subnetted)

37 TCP/IP Protocol Suite37 Addresses in a network with and without subnetting

38 TCP/IP Protocol Suite38 Default mask and subnet mask

39 TCP/IP Protocol Suite39 Comparison of a default mask and a subnet mask

40

41 Placement and operation of a NAT box.

42 19.42 A NAT implementation

43 19.43 Addresses in a NAT

44 19.44 NAT address translation

45 Introduction1-45 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

46 46 ICMP V4 -Introduction  The IP protocol has no error-reporting or error correcting mechanism.  What happens if something goes wrong? What happens if a router must discard a datagram because it cannot find a router to the final destination, or  Because the time-to-live field has a zero value?  These are examples of situations where an error has occurred and the IP protocol has no built-in mechanism to notify the original host.  The solution is ICMP protocol

47 47 Position of ICMP in the network layer

48 48 ICMP encapsulation

49 49 ICMP V4 -MESSAGES  ICMP messages are divided into two broad categories: 1.error-reporting messages 2. query messages.  The error-reporting messages report problems that a router or a host (destination) may encounter when it processes an IP packet.  The query messages, help a host or a network manager get specific information from a router or another host. Also, hosts can discover and learn about routers on their network and routers can help a node redirect its messages.

50 50 General format of ICMP messages or ICMP header

51  Headers are 32 bits in length; all contain same three fields ◦ type - 8 bit message type code  Thirteen message type are defined ◦ code - 8 bit; indicating why message is being sent ◦ checksum - standard internet checksum  for purpose of calculation the checksum field is set to zero

52 52

53 53 Error-reporting messages

54 Query Messages Echo Request Timestamp Reply Timestamp Request Echo Reply

55 55 ICMP V6- INTRODUCTION  Another protocol that has been modified in version 6 of the TCP/IP protocol suite is ICMP.  This new version, Internet Control Message Protocol version 6 ( ICMPv6 ), follows the same strategy and purposes of version 4.  ICMPv6, however, is more complicated than ICMPv4: some protocols that were independent in version 4 are now part of ICMPv6 and  some new messages have been added to make it more useful.

56 56 Comparison of network layers in version 4 and version 6

57 57 Taxonomy of ICMPv6 messages

58 58 ICMP V6- ERROR MESSAGES  As we saw in our discussion of version 4, one of the main responsibilities of ICMP is to report errors.  Four types of errors are handled: 1.destination unreachable, 2.packet too big, 3.time exceeded, and 4.parameter problems

59 59 Error-reporting messages

60 60 ICMP V6- INFORMATIONAL MESSAGES  Two of the ICMPv6 messages can be categorized as informational messages: echo request and echo reply messages.  The echo request and echo response messages are designed to check if two devices in the Internet can communicate with each other.  A host or router can send an echo request message to another host; the receiving computer or router can reply using the echo response message.

61 61 ICMP V6- NEIGHBOR-DISCOVERY MESSAGES  Several messages in the ICMPv6 have been redefined in ICMPv6 to handle the issue of neighbor discovery.  Some new messages have also been added to provide extension.  The most important issue is the definition of two new protocols that clearly define the functionality of these group messages: 1.Neighbor-Discovery (ND) protocol 2.Inverse-Neighbor-Discovery (IND) protocol.  These two protocols are used by nodes (hosts or routers) on the same link (network).

62 Introduction1-62 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

63  New countries with differing administrative policies  IPv4 same for about 20 years  Since IPv4 designed ◦ Enhanced processor performance ◦ Memory size increased ◦ Network bandwidth for Internet backbone increased ◦ New LAN technologies ◦ Number of hosts on Internet risen to over 56 million 63

64  Support billions of hosts  Reduce size of routing tables  Simplify protocol, to allow routers to process packets faster  Provide better security  Pay more attention to type of service  Make it possible for hosts to roam without changing its address

65  Despite many conceptual similarities IPv6 changes most protocol details  Completely revises datagram format ◦ Replace IPv4 variable length fields with a series of fixed format headers  Still supports connectionless delivery  Allows sender to choose datagram size but requires sender to specify maximum hops 65

66  Includes facilities for fragmentation and source routing  Main changes introduced are 1. Larger Addresses: IPv6 quadruples the size from 32 bits to 128 bits 2. Extended Address Hierarchy: Creates ability to have additional address levels on an internet  IPv4 Addresses – 2 levels, Network and Host  IPv6 Addresses – Can define a hierarchy of ISPs as well as hierarchy within a site 66

67 3. Flexible Header Format: Datagram format entirely different ◦ Defines a fixed size (40 octets) header with optional extended headers 4. Improved Options: ◦ Has same options as IPv4 plus some new ones 5. Provision for Protocol Extension: ◦ Move away from protocol that fully specifies all details to one that permits additional features 67

68 6. Support for Autoconfiguration and Renumbering (Plug and Play) ◦ Allows computers on an isolated network to assign themselves addresses and begin communicating without depending on a router or manual configuration ◦ Facility to permit a manager to renumber networks dynamically 7. Support for Resource Allocation: ◦ Two facilities for pre-allocation of network resources  a Flow abstraction  a Differentiated Services specification 68

69 19.69 IPv6 ADDRESSES Despite all short-term solutions, address depletion is still a long-term problem for the Internet. This and other problems in the IP protocol itself have been the motivation for IPv6. Structure Address Space Topics discussed in this section:

70 An IPv6 address is 128 bits long. Note

71 © MMII JW RyderCS 428 Computer Networking71  How big is ?  So large that everyone on earth will have enough addresses to have their own internets with as many addresses as the current Internet has  So large that there would be internet addresses per each square meter on earth  So large that the address space is greater than 3.4 * ◦ If addresses are assigned at the rate of 1,000,000 every microsecond (1/1,000,000 th of a second), it would take more than years to assign all possible addresses

72 IPv6 address in binary and hexadecimal colon notation

73 Abbreviated IPv6 addresses

74 © MMII JW RyderCS 428 Computer Networking74  128 bit number expressed as dotted decimal becomes 68E6:8C64:FFFF:FFFF:0:1180:96A:FFFF  Hex notation allows zero compression ◦ A string of repeated zeros is replaced with a pair of colons ◦ FF05:0:0:0:0:0:0:B3 becomes FF05::B3 ◦ Can be applied only once in any address

75 © MMII JW RyderCS 428 Computer Networking75 0:0:0:0:0:0: becomes ::  Looks quite similar to IPv4 12AB::CD30:0:0:0:0/60 says use first 60 bits and becomes 12AB CD3

76 76  Unicast – Destination address specifies a single computer. Route datagram along shortest path.  Anycast – Destination is a set of computers, possibly at different locations, that all share a single address. Route datagram along shortest path and deliver to exactly one member of the group (i.e. closest member)  Multicast - Destination is a set of computers, possibly at different locations. One copy of the datagram will be delivered to each member of the group using hardware multicast or broadcast if viable.

77 The IPv6 fixed header (required).

78  Version (4-bits): It represents the version of Internet Protocol  Traffic Class (8-bits): These 8 bits are divided into two parts. The most significant 6 bits are used for Type of Service to let the Router Known what services should be provided to this packet. The least significant 2 bits are used for Explicit Congestion Notification (ECN).

79  Flow Label (20-bits): This label is used to maintain the sequential flow of the packets belonging to a communication. The source labels the sequence to help the router identify that a particular packet belongs to a specific flow of information. This field helps avoid re-ordering of data packets. It is designed for streaming/real- time media.  Payload Length (16-bits): This field is used to tell the routers how much information a particular packet contains in its payload.

80  Next Header (8-bits): This field is used to indicate either the type of Extension Header.  Hop Limit (8-bits): This field is used to stop packet to loop in the network infinitely. The value of Hop Limit field is decremented by 1 as it passes a link (router/hop). When the field reaches 0 the packet is discarded.  Source Address (128-bits): This field indicates the address of originator of the packet.  Destination Address (128-bits): This field provides the address of intended recipient of the packet.

81 Format of an IPv6 datagram

82 Extension header types

83 5-69

84 FeatureIPv4IPv6 Source and destination address 32 bits128 bits Address FormatDotted DecimalHexadecimal Notation No of Address2^322^128 IPSecOptionalrequired Payload ID for QoS in the header No identificationUsing Flow label field FragmentationBoth router and the sending hosts Only supported at the sending hosts Header checksum includedNot included Resolve IP address to a link layer address broadcast ARP request Multicast Neighbor Solicitation message

85 FeatureIPv4IPv6 Determine the address of the best default gateway ICMP Router Discovery(optional) ICMPv6 Router Solicitation and Router Advertisement (required) Send traffic to all nodes on a subnet BroadcastLink-local scope all- nodes multicast address Configure addressManually or DHCPAutoconfiguration Manage local subnet group membership (IGMP)Multicast Listener Discovery (MLD)

86 Introduction1-86 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

87 87 ARP and RARP

88 88 Position of ARP and RARP in TCP/IP protocol suite Notice that ARP and RARP are supplemental to IP.

89 ARP (Address Resolution Protocol) 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. The delivery of a packet to a host or a router requires two levels of addressing: logical and physical. We need to be able to map a logical address to its corresponding physical address and vice versa. These can be done using either static or dynamic mapping. Logical address to physical address translation can be done statically (not practical) or dynamically (with ARP).

90 90 Position of ARP in TCP/IP protocol suite

91 91 ARP operation

92 92 ARP packet

93 93 An ARP request is broadcast; an ARP reply is unicast. Note

94 94 RARP (Reverse Address resolution Protocol) RARP finds the logical address for a machine that only knows its physical address. RARP requests are broadcast, RARP replies are unicast. This if often encountered on thin-client workstations. No disk, so when machine is booted, it needs to know its IP address (don’t want to burn the IP address into the ROM). 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.

95 95 RARP operation

96 96 RARP packet

97  when diskless workstation is booted. Such m/c get the binary image of its operating system from remote file server. But how does it learn its IP address?  The first solution to this problem was RARP used to map Ethernet address to IP address.  Next solution is BOOTP. But problem with BOOTP is that it requires manual configuration of tables mapping IP address to Ethernet address  Next come DHCP allows both manual IP address assignment and automatic assignment

98 Introduction1-98 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

99 99OBJECTIVES:  To discuss addressing issues related to a mobile host and the need for a care-of address.  To discuss two agents involved in mobile IP communication, the home agent and the foreign agent, and how they communicate.  To explain three phases of communication between a mobile host and a remote host: agent discovery, registration, and data transfer.  To mention inefficiency of mobile IP in two cases, double crossing and triangular routing, and a possible solution.

100 100 Outline 1 Addressing 2 Agents 3 Three Phases 4 Inefficiency in Mobile IP

101 101 1 ADDRESSING The main problem that must be solved in providing mobile communication using the IP protocol is addressing.

102 TCP/IP Protocol Suite 102 Topics Discussed in the Section Stationary Host Mobile Host

103 TCP/IP Protocol Suite 103 The IP addresses are designed to work with stationary hosts because part of the address defines the network to which the host is attached. Note

104 TCP/IP Protocol Suite 104 Figure 10.1 Home address and care-of address

105 TCP/IP Protocol Suite 105 Mobile IP has two addresses for a mobile host: one home address and one care-of address. The home address is permanent; the care-of address changes as the mobile host moves from one network to another. Note

106 TCP/IP Protocol Suite AGENTS To make the change of address transparent to the rest of the Internet requires a home agent and a foreign agent.

107 TCP/IP Protocol Suite 107 Topics Discussed in the Section Home Agent Foreign Agent

108 TCP/IP Protocol Suite 108 Figure 10.2 Home agent and foreign agent

109 TCP/IP Protocol Suite THREE PHASES To communicate with a remote host, a mobile host goes through three phases: agent discovery, registration, and data transfer. The first phase, agent discovery, involves the mobile host, the foreign agent, and the home agent. The second phase, registration, also involves the mobile host and the two agents. Finally, in the third phase, the remote host is also involved. We discuss each phase separately.

110 TCP/IP Protocol Suite 110 Topics Discussed in the Section Agent Discovery Registration Data Transfer

111 TCP/IP Protocol Suite 111 Figure Remote host and mobile host configuration

112 TCP/IP Protocol Suite 112 Figure Data transfer

113 Introduction1-113 Chapter 3: ROAD MAP  Basics of IPV4  ICMPV4 and ICMPV6  IPV6 in details(Motivation,features,Address Representation,Unicast and /Multicast Addresses, Header format)  ARP  RARP  Mobile IP  Distance Vector Routing Agorithm  Link State Routing Algorithm  RIP  OSPF  BGP

114 TCP/IP Protocol Suite114  To introduce the idea of autonomous systems (ASs) that divide the Internet into smaller administrative regions.  To discuss the idea of distance vector routing and the RIP that is used to implement the idea.  To discuss the idea of link state routing as the second intra-AS routing method and OSPF that is used to implement the idea.  To discuss the idea of path vector routing as the dominant inter-AS routing method and BGP that is used to implement the idea.

115 115 Outline 1 Introduction 2 Intra- and Inter-Domain Routing 3 Distance Vector Routing 4 RIP 5 Link State Routing 6 OSPF 7 Path Vector Routing 8 BGP

116 TCP/IP Protocol Suite116 1 INTRODUCTION An internet is a combination of networks connected by routers. When a datagram goes from a source to a destination, it will probably pass through many routers until it reaches the router attached to the destination network.

117 TCP/IP Protocol Suite117 Topics Discussed in the Section Cost or Metric Static versus Dynamic Routing Table Routing Protocol

118  The Optimality Principle  Shortest Path Routing  Flooding  Distance Vector Routing  Link State Routing  Hierarchical Routing  Broadcast Routing  Multicast Routing  Routing for Mobile Hosts  Routing in Ad Hoc Networks

119 TCP/IP Protocol Suite119 2 INTER- AND INTRA-DOMAIN ROUTING  Today, an internet can be so large that one routing protocol cannot handle the task of updating the routing tables of all routers.  For this reason, an internet is divided into autonomous systems.  An autonomous system (AS) is a group of networks and routers under the authority of a single administration.  Routing inside an autonomous system is called intra-domain routing.  Routing between autonomous systems is called inter- domain routing

120 TCP/IP Protocol Suite120 Figure Autonomous systems

121  Collection of networks with same policy  Single routing protocol  Usually under single administrative control AS 100 A

122  Identified by ‘AS number’  Examples: ◦ - service provider ◦ - multihomed customers ◦ - anyone needing policy descrimination

123 TCP/IP Protocol Suite123 Popular routing protocols

124 Interior Gateway ProtocolWithin an Autonomous System Carries information about internal prefixes Examples—OSPF, ISIS, EIGRP…

125 Exterior Gateway Protocol Used to convey routing information between Autonomous Systems Decoupled from the IGPCurrent EGP is BGP

126 TCP/IP Protocol Suite126 3 DISTANCE VECTOR ROUTING Today, an internet can be so large that one routing protocol cannot handle the task of updating the routing tables of all routers. For this reason, an internet is divided into autonomous systems. An autonomous system (AS) is a group of networks and routers under the authority of a single administration. Routing inside an autonomous system is called intra-domain routing.

127  No node has complete information about the costs of all network links  Gradual calculation of path by exchanging information with neighbors  Each node constructs a one-dimensional array containing the “distances” or “costs” to all other nodes (as it relates to its knowledge) and distributes it to its immediate neighbors.  Key thing -- each node knows the cost of links to its neighbors.  If no link exists between two nodes, the cost of a direct link between the nodes is “infinity”.

128 TCP/IP Protocol Suite128 Periodic Update A node sends its routing table, normally 30 seconds, in a periodic update Triggered Update A node sends its routing table to its neighbors any time when there is a change in its routing table 1. After updating its routing table, or 2. Detects some failure in the neighboring links

129 TCP/IP Protocol Suite129 If the next-node entry is different The receiving node chooses the row with the smaller cost If the next-node entry is the same i.e. the sender of the new row is the provider of the old entry The receiving node chooses the new row, even though the new value is infinity.

130 (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.

131

132 TCP/IP Protocol Suite132 RIP- Routing Information Protocol The Routing Information Protocol (RIP) is an intra-domain (interior) routing protocol used inside an autonomous system. It is a very simple protocol based on distance vector routing. In the Internet, goal of routers is to learn how to forward packets to various networks.

133 Routers advertise the cost of reaching networks. In this example, C’s update to A would indicate that C can reach Networks 2 and 3 with cost 0, Networks 5 and 6 with cost 1and Network 4 with cost 2.

134 TCP/IP Protocol Suite134 Request A request message is sent by a router that has just come up or by a router that has some time- out entries A request can ask about specific entries or all entries Response A response can be within 30s or when there is a change in the routing table

135 TCP/IP Protocol Suite135 Periodic timer Routing tables are exchanged every 30 seconds using the RIP advertisement. Expiration timer If a router does not hear from its neighbor once every 180 seconds, the neighbor is deemed unreachable.

136 TCP/IP Protocol Suite136 LINK STATE ROUTING  Link state routing has a different philosophy from that of distance vector routing.  In link state routing, if each node in the domain has the entire topology of the domain] —the list of nodes and links, how they are connected including the type, cost (metric), and the condition of the links (up or down) —the node can use the Dijkstra algorithm to build a routing table.

137 Discover its neighbors, learn their network address.Measure the delay or cost to each of its neighbors.Construct a packet telling all it has just learned.Send this packet to all other routers. Compute the shortest path to every other router.

138 (a) Nine routers and a LAN. (b) A graph model of (a). Hello packets are used to find Neighbors

139 Echo packets are used to measure the line cost Calculate total time used to echo packett = Arrival time – Departure timeThen t/2 gives cost(time) of line

140 (a) A subnet. (b) The link state packets for this subnet.

141 The packet buffer for router B in the previous slide

142 TCP/IP Protocol Suite142 OSPF- Open Shortest Path First The Open Shortest Path First (OSPF) protocol is an intra- domain routing protocol based on link state routing. Its domain is also an autonomous system.Support variety of distance metrics Dynamic algorithm that adapted to changes in the topology automatically and quickly

143 Support routing based on type of service Do load balancing, splitting the load over multiple lines Prevent spoofing ie better security provision Provision for dealing with routers that were connected to the internet via a tunnel

144  OSPF divides AS into areas. Every AS has a backbone area called area 0 All areas are connected to backbone areas  OSPF has four classes of router 1. Internal routers -wholly within on area 2. Area border routers -connect two or more areas 3. Backbone routers -On the backbone area 4. AS boundary routers -Talk to other routers in other AS

145 The relation between ASes, backbones, and areas in OSPF.

146 The five types of OSPF messeges. 5-66

147 Border Gateway Protocol (BGP) is an interdomain routing protocol using path vector routing. It first appeared in 1989 and has gone through four versions. The Border Gateway Protocol makes routing decisions based on paths, network policies or rule-sets configured by a network administrator, network administrator TCP/IP Protocol Suite147 BGP- Border Gateway Protocol

148 When BGP runs between two peers in the same autonomous system (AS), it is referred to as Internal BGP (iBGP or Interior Border Gateway Protocol).autonomous system When it runs between different autonomous systems, it is called External BGP (EBGP or Exterior Border Gateway Protocol). Routers on the boundary of one AS exchanging information with another AS are called border or edge routers

149 TCP/IP Protocol Suite149 Types of BGP messages

150 Lecture #13: Open Announces AS ID Determines hold timer – interval between keep_alive or update messages, zero interval implies no keep_alive Keep_alive Sent periodically to peers to ensure connectivity. Notification Used for error notification TCP connection is closed immediately after notification

151 (a) A set of BGP routers. (b) Information sent to F.

152 TCP/IP Protocol Suite152 ORIGIN The source of the routing information (RIP, OSPF, etc) AS_PATH The list of ASs through which the destination can be reached NEXT-HOP The next router to which the data packet should be sent

153 TCP/IP Protocol Suite153 BGP uses the services of TCP on port 179. Note

154


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