Chabot College

1. Chabot College ELEC 99.05 Addressing & Routing Foundation Concepts

2. Switches & Bridges (review) • Layer-2 device • Reduce large collision domains • Uses MAC address table to determine whether or not to forward a frame

3. Switches & Bridges (review) • Make “low level” decisions • Flood the network if address unknown • Always forwards broadcasts • Excess broadcast traffic can result

4. Layer 2 Switch Limitations Switches & Bridges: • Don’t handle device moves well • Can’t control broadcast traffic • Lack path determination abilities • Have limited address capacity

5. Layer 2 Switch Limitations • Switch doesn’t handle device moves well. • When a device is moved from one switch port to another, the switch’s MAC address table will be wrong until it is “flushed” or “ages out”.

6. Layer 2 Switch Limitations • Switch can’t control broadcast traffic. • Switches (and bridges) always forward broadcast traffic, which is essential to LAN operation. • Broadcasts only stop at the edge of the network. • Excess broadcast traffic can result.

7. Layer 2 Switch Limitations • Path determination abilities • Almost no ability to determine paths when there are multiple routes from source to destination. • No ability to change paths when a route becomes unavailable.

8. Layer 2 Switch Limitations • Limited address capacity • There are 10’s of millions of MAC addresses in the world, but the typical switch can store only a few thousand MACs. • Fine for LANs, but inadequate for internetworks (networks of networks). • This is the key limitation!

9. 3 Layer 3 solves these problems! • Allows device moves throughlogical addresses. • Uses routers to control broadcast propagation. • Provides path determinationthrough routing. • Uses hierarchical addressesto support world-wide addressing.

10. Logical Order In order to impose logical order on a network, a different kind of address needs to be used. Network Layer Logical Address (Software) Data Link Layer Physical Address (Hardware) Physical Layer No address

11. Physical v. Logical Address • Physical Address • Layer 2 • aka MAC address, hardware address, Ethernet address • burned in card • can’t be changed without changing card • flat scheme (like Social Security Numbers) • Analogy: your name

12. Physical v. Logical Address • Logical Address • Layer 3 • aka protocol address • set by administrator in software • can be easily changed • hierarchical scheme like Phone Numbers (area code, prefix) or ZIP codes • Analogy: your mailing address

13. Layer 3 addresses • Logical or Layer 3 addresses come in different flavors, depending on the layer-3 protocol used: • TCP/IP = IP address • Novell IPX = IPX address • AppleTalk = AT address etc.

14. Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Addresses at Layers TCP/IP or IPX/SPX or AppleTalk Logical address MAC address Ethernet

15. Logical Address Composition Though the exact length and format of a logical (layer 3) address differs depending on the protocol, all logical addresses share this basic formula: NETWORK NUMBER HOST NUMBER

16. Logical Addresses Explained Phone Numbers: 510-723-7464 = Alameda County 510-723-7464 = Hayward Exchange 510-723-7464 = Particular Hayward Phone

17. Logical Addresses Examples • AppleTalk address network 400, host 22 • IPX (Novell) network 4b39, host 00c0.4f31.03d2 • IP (Internet) network 207.81.104, host 15 400:22 4b39.00c0.4f31.03d2 207.81.104.15

18. Logical Addresses Explained • AppleTalk address network 400, host 22 • IPX (Novell) network 4b39, host 00c0.4f31.03d2 • IP (Internet) network 207.81.104, host 15 400:22 4b39.00c0.4f31.03d2 207.81.104.15

19. Logical Addresses Explained • AppleTalk address network 400, host 22 • IPX (Novell) network 4b39, host 00c0.4f31.03d2 • IP (Internet) network 207.81.104, host 15 400:22 4b39.00c0.4f31.03d2 207.81.104.15

20. Routers • Routers: • internetworking devices that work at Layer 3 • understand and use logical addresses • keep tables of information about networks • can make path determinations • don’t normally forward broadcasts • can support multiple layer 3 protocols (TCP/IP, IPX, AppleTalk) at the same time

21. R R R R Routers at work Don’t know Z, but I know net #7. NETWORK 1 NETWORK 2 NETWORK 3 A Node 1.A is sending to Node 7.Z NETWORK 4 NETWORK 5 NETWORK 6 NETWORK 7 Z

22. The IP Address IP addresses are made up of 32 bits: 10101001110001110100010110001001

23. Binary IP Addresses In the binary numbering system, each digit has two possible values: 0 or 1

24. Binary IP Addresses Each value is a binary digit, or bit for short. 01111000 Eight bits together make a unit called a byte. In IP addresses, bytes are called octets (group of eight).

25. Binary IP Addresses An octet that is all zeros has a decimal value of 0: Binary = 00000000 Decimal = 0

26. Binary IP Addresses An octet that is all ones has a decimal value of 255: Binary = 11111111 Decimal = 255

27. Binary IP Addresses In decimal, each place value is a power of ten. We read the number 2342 as two-thousand three-hundred forty-two. 103 102 101 100 1000 100 10 1 2 3 4 2

28. Binary IP Addresses In binary, each place value is a power of two. The octet 11001111 is equivalent to 207 in decimal. 27 26 25 24 23 22 21 20 128 64 32 16 8 4 2 1 1 1 0 0 1 1 1 1

29. Binary IP Addresses The 32 bits of an IP address are grouped into 4 bytes: 10101001110001110100010110001001 10101001 11000111 01000101 10001001

30. IP Addresses We use dotted notation to represent the value of each byte (octet) of the IP address in decimal. 10101001 11000111 01000101 10001001 16919969137

31. IP Addresses An IP address has two parts: • network number • host number

32. IP Addresses • Which bits refer to the network number? • Which bits refer to the host number?

33. IP Addresses • The answers to these questions vary. • To find out for a specific address, you need to know how to convert decimal numbers to binary numbers (and back again).