Transcript Logical Address - Chabot College

Chabot College
ELEC 99.05
Addressing & Routing Foundation Concepts
CISCO NETWORKING ACADEMY
Switches & Bridges (review)
• Layer-2 device
• Reduce large collision domains
• Uses MAC address table to
determine whether or not to forward
a frame
CISCO NETWORKING ACADEMY
Switches & Bridges (review)
• Make “low level” decisions
• Flood the network if address
unknown
• Always forwards broadcasts
– Excess broadcast traffic can result
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
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”.
CISCO NETWORKING ACADEMY
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.
CISCO NETWORKING ACADEMY
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.
CISCO NETWORKING ACADEMY
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!
CISCO NETWORKING ACADEMY
Layer 3 solves these problems!
• Allows device moves through
logical addresses.
• Uses routers to control broadcast
propagation.
• Provides path determination
through routing.
• Uses hierarchical addresses
to support world-wide
addressing.
CISCO NETWORKING ACADEMY
3
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
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
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.
CISCO NETWORKING ACADEMY
Addresses at Layers
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
CISCO NETWORKING ACADEMY
TCP/IP or IPX/SPX or
AppleTalk
Logical address
MAC address
Ethernet
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
CISCO NETWORKING ACADEMY
HOST NUMBER
Logical Addresses Explained
Phone Numbers:
510-723-7464 = Alameda County
510-723-7464 = Hayward Exchange
510-723-7464 = Particular Hayward Phone
CISCO NETWORKING ACADEMY
Logical Addresses Examples
• AppleTalk address
400:22
network 400, host 22
• IPX (Novell)
4b39.00c0.4f31.03d2
network 4b39, host 00c0.4f31.03d2
• IP (Internet)
207.81.104.15
network 207.81.104, host 15
CISCO NETWORKING ACADEMY
Logical Addresses Explained
• AppleTalk address
400:22
network 400, host 22
• IPX (Novell)
4b39.00c0.4f31.03d2
network 4b39, host 00c0.4f31.03d2
• IP (Internet)
207.81.104.15
network 207.81.104, host 15
CISCO NETWORKING ACADEMY
Logical Addresses Explained
• AppleTalk address
400:22
network 400, host 22
• IPX (Novell)
4b39.00c0.4f31.03d2
network 4b39, host 00c0.4f31.03d2
• IP (Internet)
207.81.104.15
network 207.81.104, host 15
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
Routers at work
Don’t know
Z, but I know
net #7.
NETWORK 1
NETWORK 2
R
A
R
NETWORK 4
NETWORK 5
NETWORK 3
Node 1.A is sending to Node 7.Z
NETWORK 6
R
NETWORK 7
R
Z
CISCO NETWORKING ACADEMY
The IP Address
IP addresses are made up of 32 bits:
10101001110001110100010110001001
CISCO NETWORKING ACADEMY
Binary IP Addresses
In the binary numbering system,
each digit has two possible values:
0 or 1
CISCO NETWORKING ACADEMY
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).
CISCO NETWORKING ACADEMY
Binary IP Addresses
An octet that is all zeros has a
decimal value of 0:
Binary = 00000000
Decimal = 0
CISCO NETWORKING ACADEMY
Binary IP Addresses
An octet that is all ones has a
decimal value of 255:
Binary = 11111111
Decimal = 255
CISCO NETWORKING ACADEMY
Binary IP Addresses
In decimal, each place value is a
power of ten.
103
102
101
100
1000
100
10
1
2
3
4
2
We read the number 2342 as twothousand three-hundred forty-two.
CISCO NETWORKING ACADEMY
Binary IP Addresses
In binary, each place value is a power of
two.
27
26
25
24
23
22
21
20
128
64
32
16
8
4
2
1
1
1
0
0
1
1
1
1
The octet 11001111 is equivalent to 207
in decimal.
CISCO NETWORKING ACADEMY
Binary IP Addresses
The 32 bits of an IP address are
grouped into 4 bytes:
10101001110001110100010110001001
10101001 11000111 01000101 10001001
CISCO NETWORKING ACADEMY
IP 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
CISCO NETWORKING ACADEMY
IP Addresses
An IP address has two parts:
– network number
– host number
CISCO NETWORKING ACADEMY
IP Addresses
• Which bits refer to the network
number?
• Which bits refer to the host
number?
CISCO NETWORKING ACADEMY
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).
CISCO NETWORKING ACADEMY