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Chapter Overview

Chapter Overview. Subnet. What is a subnet. When you break a network into a few smaller networks, you have created several subnets Like IP address where we have network addresses and host IDs, we now have subnet addresses and host IDs. What Is a Subnet Mask?.

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Chapter Overview

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  1. Chapter Overview • Subnet

  2. What is a subnet • When you break a network into a few smaller networks, you have created several subnets • Like IP address where we have network addresses and host IDs, we now have subnet addresses and host IDs

  3. What Is a Subnet Mask? • A subnet mask is a 32-bit binary number that indicates which bits of an IP address identify the network and which bits identify the host. • The 1 bits are the network identifier bits and the 0 bits are the host identifier bits. • A subnet mask is typically expressed in dotted decimal notation.

  4. Subnet Masks for IP Address Classes

  5. Creating Subnets • Borrow bits from the host identifier and use them as a subnet identifier. • Convert the binary values to decimals.

  6. Subnetting a Class B Address

  7. Classless Inter-Domain Routing (CIDR) • (CIDR) is an Internet Protocol (IP) address allocation and route aggregation methodology used within the Internet addressing architecture that replaced the IPv4 classful network organization of the IP address space.

  8. CIDR notation • In the CIDR notation, the IP address is expressed according to the standards of IPv4 or IPv6, followed by the separator character which is a slash (/), followed by the prefix size as a decimal number. • the address specification 192.168.100.1/24 represents the given IPv4 address and its associated routing prefix 192.168.100.0 or, equivalently, its subnet mask, 255.255.255.0.

  9. CIDR notation (2) • You cannot have 192.168.100.1/31 because the hosts need to have at least two bits

  10. The five key questions of a subnet mask • How many subnets does a subnet mask produce? • Number of valid hosts per subnet • What are the valid subnets • What are the broadcast address of each subnet • What are the valid hosts in a subnebt

  11. How many subnets • 2x where x is the number of 1s in the subnet mask after the 1s for the traditional class (8 for A, 16 for B, and 24 for C) • For example, the subnet mask 255.255.255.192 would have 22=4 subnet for a class C network.

  12. Number of valid hosts per subnet • 2y -2, where y is the number of zeros in a subnet mask, is the number of hosts • The -2 are for all 0s and all 1s. • For 255.255.255.192, the number of hosts are 26 -2 = 62

  13. What are the valid subnets • For 255.255.255.192 on a class C network they are • 0, (00000000 to 00111111) • 64, (01000000 to 01111111) • 128, (10000000 to 10111111) and • 192 , (11000000 to 11111111)

  14. What are the broadcast address • For 255.255.255.192 they are • 0  00111111 • 64  01111111 • 128  10111111 • 192  11111111

  15. What are the valid hosts • For 255.255.255.192 they are • 0, (00000001 to 00111110) • 64, (01000001 to 01111110) • 128, (10000001 to 10111110) and • 192 , (11000001 to 11111110)

  16. Example #1C (Page 219) • On mask of 255.255.255.128/25 • # of subnet 2 • Hosts in each subnet 126 • The two subnets are 0 and 128, which broadcast address be 127 and 255 respectively • Valid host addresses

  17. Assigning IP addresses • Note, this 192.168.0.0 ~192.168.255.255 are class C private IP addresses

  18. Troubleshooting • 1. Ping 127.0.0.1 (or ::1) • If cannot connect, host problems • NIC, TCP/IP, subnet mask, etc • Ping IP address of the host • If works, NIC is working • Ping the default gateway • If works, connected to LAN • If not, most likely physical layer issues • Ping server • If working, the server is working, so is IP • If not, server could be down, or others

  19. What’s wrong here (pp. 237) It is a broadcast address

  20. Tools • Ping (Packet Internet groper) • Traceroute/tracert • Arp –a • Ipconfig

  21. Network Address Translation (NAT) • Access the Internet with private IP address • Change ISP without renumbering computer’s IP addresses • Merge two networks with some duplicated IP addresses

  22. NAT where?

  23. Good and bad

  24. Three types of translations • Static – allow one to one mapping of local and global address, use to hide internal addresses • Dynamic – doing the same as Static, just need a pool of real IP addresses • Overloading – most interesting, used by home Internet routers – using ports

  25. Example of overloading

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