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CENG415 – Communication Networks

CENG415 – Communication Networks. Lectures 13 Network layer. Chapter 4 – Network layer. 4. 1 Introduction 4.4 IP: Internet Protocol IP V4 addressing 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.5 Routing algorithms 4.6 Routing in the Internet

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CENG415 – Communication Networks

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  1. CENG415 – Communication Networks Lectures 13 Network layer

  2. Chapter 4 – Network layer 4. 1 Introduction 4.4 IP: Internet Protocol • IP V4 addressing 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.5 Routing algorithms 4.6 Routing in the Internet 4.7 Broadcast and multicast routing

  3. Network layer • transport segment from sending to receiving host • on sending side encapsulates segments into datagrams • on receiving side, delivers segments to transport layer • network layer protocols in every host, router • Router examines header fields in all IP datagrams passing through it

  4. Two network layer functions • forwarding: move packets from router’s input to appropriate router output • routing: determine route taken by packets from source to destination • routing algorithms

  5. Chapter 4 – Network layer 4. 1 Introduction 4.4 IP: Internet Protocol • IP V4 addressing 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.5 Routing algorithms 4.6 Routing in the Internet 4.7 Broadcast and multicast routing

  6. 223.1.1.2 223.1.2.1 223.1.3.27 223.1.3.1 223.1.3.2 223.1.2.2 IP Addressing • IP address: 32-bit identifier for host, and router interface • interface: connection between host/router and physical link (sometimes called a "port"). • router’s typically have multiple interfaces • host typically has one interface • IP addresses associated with each interface 223.1.1.1 223.1.2.9 223.1.1.4 223.1.1.3 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1

  7. IP Addressing - Review • IP addressing is the method used to identify hosts and network devices. • In order to send and receive messages on an IP network, every network host must be assigned a unique 32 bit IP address. • large binary numbers are difficult for humans to read and understand • IP addresses are usually displayed in dotted-decimal notation • each of the four octets is converted to a decimal number separated by a decimal point

  8. IP Addressing - Classes • The 32-bit address space was organized into five classes. • Three of these classes, A, B, and C, provide addresses that can be assigned to individual hosts or networks. • Class D is reserved for multicast (will be explained later) • Class E is reserved for experimental use

  9. IP Addressing - Classes

  10. IP Addressing - Classes NOTE: To send a message to all the hosts in a network we use the broadcasting address. Broadcasting address is the IP address where all the host bits are set to 1.

  11. IP Addressing - Classes

  12. IP Addressing - Classes

  13. IP Addressing -Subnet • Organizations with thousands of hosts rarely had them all in one place. • Some organizations wanted to separate individual departments from each other for security purposes. • To solve these problems, the organizations leading the development of the Internet chose to partition their networks into mini-networks, or subnets, using a process called subnetting. • How does a single class B network get split into multiple networks, in a way that each subnet is treated as a separate network? • RFC 917, Internet Subnets, defines the subnet mask as the method routers use to isolate a subnet from an IP address.

  14. IP Addressing -Subnet • The subnet mask is read from left to right, bit for bit. • If a bit in the subnet mask is set to 1, it indicates that the value in that position is part of the network ID. • A 0 in the subnet mask indicates that the value in that position is part of the host ID. • The two-level hierarchy of classed addressing included a network ID and a host ID. • In classfulsubnetting, the network ID is left alone, and the host ID is divided into a subnet ID and a new host ID. • For example, a Class B network has a 16-bit default subnet mask of 11111111 11111111 00000000 00000000, or 255.255.0.0. That leaves 16-bits for the host ID.

  15. IP Addressing -Subnet • One way to divide a class B into multiple networks is to use two of the host bits as a subnet ID. • There is now a 18-bit subnet mask of 255.255.192.0, and only 14-bits remain for the host ID.   • Partitioning the host ID this way always results in a fixed number of subnets and a fixed number of hosts per subnet.

  16. IP Addressing -Subnet Example: 160.211.0.0 is a class B network Network IP: 10100000 11010011 00000000 00000000 Mask: 11111111 11111111 00000000 00000000 This is one network that can support 65534 hosts. Divide into 4 subnets, for each subnet specify the Network IP, the subnet Mask, the rang of IPs and the broadcasting IP.

  17. IP Addressing -Subnet Divide into 4 subnets, two bits are used. The 4 resulting networks are: Network 1: 10100000 11010011 00000000 00000000 160.211.0.0 Mask: 11111111 11111111 11000000 00000000 255.255.192.0 Range of IPs : 160.211.0.1 to 160.211.63.254 Broadcasting IP: 160.211.63.255 Network 2: 10100000 11010011 01000000 00000000 160.211.64.0 Mask: 11111111 11111111 11000000 00000000 255.255.192.0 Range of IPs : 160.211.64.1 to 160.211.127.254 Broadcasting IP: 160.211.127.255 Network 1: 10100000 11010011 10000000 00000000 160.211.128.0 Mask: 11111111 11111111 11000000 0000000 255.255.192.0 Range of IPs : 160.211.128.1 to 160.211.191.254 Broadcasting IP: 60.211.191.255 Network 1: 10100000 11010011 11000000 00000000 160.211.192.0 Mask: 11111111 11111111 11000000 00000000 255.255.192.0 Range of IPs : 160.211.192.1 to 160.211.255.254 Broadcasting IP: 60.211.255.255 These are 4 networks each of 16382 hosts (equal mask for all subnets)

  18. IP Addressing -Subnet Example: consider a class C network IP address 182.168.1.0 The table for the subnet possibilities for the 192.168.1.0 network shows how the selection of a number of bits for the subnet ID affects both the number of possible subnets and the number of hosts that can be in each subnet

  19. IP Addressing -Example Q: Consider a network with 2000 hosts. What IP class should be used? A: Class B since class C support no more than 254 hosts. So from class B we use 2000 IPs, or a class B subnet can handle up to 65534 hosts. • 65534 – 2000 = 63534 IPs are wasted. Solution: In order to allow more efficient use of IP addresses Classless Inter-Domain Routing (CIDR) was created

  20. Host part Subnet part 11001000 0001011100010000 00000000 200.23.16.0/23 OR 200.23.16.0 255.255.254.0 IP Addressing -CIDR • With CIDR, there are no more network classes • CIDR uses variable length subnet masks (VLSM) for subnetting • The network ID no longer has to be on an octet boundary CIDR • subnet portion of address of arbitrary length • address format: a.b.c.d/x, where x is # bits in subnet portion of address

  21. LAB: Practicing subnetting Objective: • Create an IP addressing plan for a small network. Consider the network 192.168.64.0 / 19 You are requested to subnet this network into for networks as indicated in the picture What is your strategy?

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