cisco networking academy chabot college elec 99.05 addressing & routing foundation concepts

CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY

Chabot CollegeChabot College

ELEC 99.05ELEC 99.05Addressing & Routing Foundation ConceptsAddressing & Routing Foundation Concepts


Switches & Bridges (review)Switches & Bridges (review)

• Layer-2 device

• Reduce large collision domains

• Uses MAC address table to determine whether or not to forward a frame


Switches & Bridges (review)Switches & Bridges (review)

• Make “low level” decisions

• Flood the network if address unknown

• Always forwards broadcasts– Excess broadcast traffic can result


Layer 2 Switch LimitationsLayer 2 Switch Limitations

Switches & Bridges:

• Don’t handle device moves well

• Can’t control broadcast traffic

• Lack path determination abilities

• Have limited address capacity



• 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”.



• 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.



• 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.



• 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!


Layer 3 solves these problems!Layer 3 solves these problems!

• Allows device moves throughlogical addresses.

• Uses routers to control broadcast propagation.

• Provides path determinationthrough routing.

• Uses hierarchical addresses to support world-wide addressing.

3


Logical OrderLogical Order

In order to impose logical order on a network, a different kind of address needs to be used.

Data Link Layer

Physical Layer

Network Layer

No address

Physical Address (Hardware)

Logical Address (Software)


Physical v. Logical AddressPhysical 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


Physical v. Logical AddressPhysical 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


Layer 3 addressesLayer 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.


Addresses at LayersAddresses at Layers

Data Link Layer

Physical Layer

Network Layer

Session Layer

Transport Layer

Presentation Layer

Application Layer

TCP/IP or IPX/SPX or AppleTalk

EthernetMAC address

Logical address


Logical Address CompositionLogical 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

NETWORK NUMBER HOST NUMBERHOST NUMBER


Logical Addresses ExplainedLogical Addresses Explained

Phone Numbers:

510-723-7464 = Alameda County

510-723-7464 = Hayward Exchange

510-723-7464 = Particular Hayward Phone


Logical Addresses ExamplesLogical Addresses Examples

• AppleTalk addressnetwork 400, host 22

• IPX (Novell)network 4b39, host 00c0.4f31.03d2

• IP (Internet)network 207.81.104, host 15

400:22400:22

4b39.00c0.4f31.03d24b39.00c0.4f31.03d2

207.81.104.15207.81.104.15


Logical Addresses ExplainedLogical Addresses Explained

• AppleTalk addressnetwork 400, host 22

• IPX (Novell)network 4b39, host 00c0.4f31.03d2

• IP (Internet)network 207.81.104, host 15

400:22400:22

4b39.00c0.4f31.03d24b39.00c0.4f31.03d2

207.81.104.15207.81.104.15


RoutersRouters

• 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


Routers at workRouters at work

RR

R R

A

Z

NETWORK 1 NETWORK 2 NETWORK 3

NE

TW

OR

K 4

NETWORK 5 NETWORK 6 NETWORK 7

Don’t know Z, but I know

net #7.

Node 1.A is sending to Node 7.Z


The IP AddressThe IP Address

IP addresses are made up of 32 bits:

10101001110001110100010110001001


Binary IP AddressesBinary IP Addresses

In the binary numbering system, each digit has two possible values:

0 or 1



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).



An octet that is all zeros has a decimal value of 0:

Binary = 00000000

Decimal = 0



An octet that is all ones has a decimal value of 255:

Binary = 11111111

Decimal = 255



In decimal, each place value is a power of ten.

We read the number 2342 as two-thousand three-hundred forty-two.

1101001000

2432

100101102103



In binary, each place value is a power of two.

The octet 11001111 is equivalent to 207 in decimal.

124

111

81632

100

64128

11

2021222324252627


Binary IP Addresses Binary IP Addresses

The 32 bits of an IP address are grouped into 4 bytes:

10101001110001110100010110001001

10101001 11000111 01000101 10001001


IP AddressesIP Addresses

We use dotted notation to represent the value of each byte (octet) of the IP address in decimal.

10101001 11000111 01000101 10001001

169 199 69 137



An IP address has two parts:

– network number– host number



• Which bits refer to the network number?

• Which bits refer to the host number?



• 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).

cisco networking academy chabot college elec 99.05 addressing & routing foundation concepts

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