1 / 22

Networks and Protocols CE00997-3

Learn about classful IP addressing, subnet masks, and how routers route packets based on IP addresses. Understand the need for subnetting and how to obtain sub-network addresses.

bsalas
Download Presentation

Networks and Protocols CE00997-3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Networks and Protocols CE00997-3 Week 4a

  2. Classful IP addressing

  3. IP ADDRESSING • These slides are for background reading only • They will not be used in the lecture, you will need to take notes from the white board

  4. Subnet masks • Subnet masks are used to indicate which bits define the network and which bits define the host. • Class A • 11111111 00000000 00000000 00000000 • 255.0.0.0 • Class B • 11111111 11111111 00000000 00000000 • 255.255.0.0 • Class C • 11111111 11111111 11111111 00000000 • 255.255.255.0

  5. IP Address Routing • Routers look at the IP address and logically “AND” it with the subnet mask to obtain the network address or ID (not the individual host). • Routers route packets based on their network address. • Routers do not know about individual hosts on remote networks.

  6. IP Address Routing • Example an IP address of 146.87.114.32 means: • 10010010 01010111 01110010 00100000 • first two bits are 10 therefore Class B (16 bit NET ID) • obtain net id by bitwise AND with class B mask 10010010 01010111 01110010 00100000 11111111 11111111 00000000 00000000 AND 10010010 01010111 00000000 00000000 Thus the NET ID is = 146.87.0.0 • Note this means a host field of all 0’s cannot be used for a specific host as it refers to the network itself (or the wire)

  7. Routing from Net 1 to Net 2 Net 1 Net 2 S0 S1 E0 S0 S1 S0 130.29.45.7 Router B 130.5.7.12 Router A Router C • Data from Host 130.29.45.7 is sent to 130.5.7.12 • Routers route the packets to network 130.5.0.0 • Router C is directly connect to this network and delivers the packets to the host.

  8. Routing from Net 1 to Net 2 130.5.7.12 AND 255.255.0.0 = 130.5.0.0 130 . 5 . 0 . 0

  9. The need for sub-netting • The destination network may be a corporate WAN • It may be international with several thousand computers • Each router would need to know the route to all devices. • It needs breaking down into smaller networks.

  10. A Sub-Netted Network 130.29.3.0 130.29.2.0 130.29.4.0 130.29.5.0 130.29.1.0 130.29.0.0 130.29.6.0 130.29.7.0 IP packet DA=130.29.5.7

  11. A Sub-Netted Network • In the Internet we route to 130.29.0.0 • Within the 130.29.0.0 network we route to 130.29.X.0 (X subnet) • How? • Use a subnet mask which extends the range of bits representing the network.

  12. Obtaining the Sub-Network Address • Example an IP address of 130.29.5.7 in a subnetted network. Subnet mask = 255.255.255.0 • obtain subnet id by bitwise AND with the subnet mask • 10000010 00011101 00000101 00000111 • 11111111 11111111 11111111 00000000 AND • = 10000010 00011101 00000101 00000000 • Thus the SubNet ID is = 130.29.5.0

  13. A Sub-Netted Network 130.29.3.0 130.29.2.0 130.29.4.0 130.29.5.0 130.29.1.0 Route to 130.29.5.0 IP packet DA=130.29.5.7 130.29.7.0 130.29.6.0

  14. Obtaining the Sub-Network Address • First network is 130.29.1.0 • First host on 1st network is 130.29.1.1 • Last host on 1st subnet is 130.29.1.254 • Broadcast on 1st subnet is 130.29.1.255 • Second network is 130.29.2.0 • First host on 2nd network is 130.29.2.1 • Last host on 2nd subnet is 130.29.2.254 • Broadcast on 2nd subnet is 130.29.2.255

  15. Obtaining the Sub-Network Address • Last network is 130.29.254.0 • First host on last network is 130.29. 254.1 • Last host on last subnet is 130.29. 254.254 • Broadcast on last subnet is 130.29. 254.255 • NOTE • The all 0’s and the all 1’s subnets are not used, as this can cause confusion with the class B address. • e.g • 130.29.0.0 (which network ?) • 130.29.255.255 (broadcast to which network?)

  16. Sub-netting • With a class A address we have 24 host bits. • We can borrow between 2 an 22 bits for a sub-net-id • With a class B address we have 16 host bits. • We can borrow between 2 an 14 bits for a sub-net-id • With a class C address we have 8 host bits. • We can borrow between 2 an 6 bits for a sub-net-id

  17. Choice of Subnet mask Consider a class C network 201.56.121.0 • Can borrow 2-6 bits for subnet • Subnet masks • 255.255.255.192 (11000000) – 2 bits • 255.255.255.224 (11100000) – 3 bits • 255.255.255.240 (11110000) – 4 bits • 255.255.255.248 (11111000) – 5 bits • 255.255.255.252 (11111100) – 6 bits

  18. Choice of Subnet mask • Borrow 2 bits SN mask 255.255.255.192 • 2bits subnet – 2 subnets (01 –10) • 6 bits for host - 62 hosts per subnet • Borrow 3 bits SN mask 255.255.255.224 • 3 bits subnet – 6 subnets (001 – 110) • 5 bits for host - 30 hosts per subnet • Borrow 4 bits SN mask 255.255.255.240 • 4 bits subnet – 14 subnets (0001 – 1110) • 4 bits for host - 14 hosts per subnet

  19. Choice of Subnet mask • Borrow 5 bits SN mask 255.255.255.248 • 5 bits subnet – 30 subnets (00001 – 11110) • 3 bits for host - 6 hosts per subnet • Borrow 6 bits SN mask 255.255.255.252 • 6 bits subnet – 62 subnets (000001 – 111110) • 2 bits for host - 2 hosts per subnet

  20. Example mask • IP Address 201.56.121.0 (201=11001001) Class C 1 1 0 Net id Host id • SN Mask 255.255.255.224 (11100000) 1 1 0 Net id SN id Host id 24 bits 3 bits 5 bits

  21. Example mask • IP Address 201.56.121.0 • SN Mask 255.255.255.224 (11100000) Subnets 201.56.121.32 (001 00000) – 1st subnet 201.56.121.64 (010 00000) – 2nd subnet 201.56.121.96 (011 00000) – 3rd subnet 201.56.121.128 (100 00000) – 4th subnet 201.56.121.160 (101 00000) – 5th subnet 201.56.121.192 (110 00000) – 6th subnet

  22. Example mask • Look at the 3rd subnet • Sub net 201.56.121.96 (011 00000) 210.56.121.96 (011 00000) – the network 210.56.121.97 (011 00001) – 1st host 210.56.121.126 (011 11110) – last host 210.56.121.127 (011 11111) – broadcast

More Related