Download ppt - Dr. Wissam Fawaz

Chapter 4: Network Layer
 4. 1 Introduction
 4.2 Virtual circuit and
datagram networks
 4.3 What’s inside a
router
 4.4 IP: Internet
Protocol




Datagram format
IPv4 addressing
ICMP
IPv6
 4.5 Routing algorithms
 Link state
 Distance Vector
 Hierarchical routing
 4.6 Routing in the
Internet



RIP
OSPF
BGP
 4.7 Broadcast and
multicast routing
Network Layer
4-1
IP Addresses
Network Layer
4-2
Special IP addresses
 The IP address 0.0.0.0
 Is
used by hosts when they are booting
 IP addresses with 0 as network number
Network Layer
 Refer to the current network
4-3
Class A, B, and C networks: default
masks without subnetting
 Routers use a default mask
 To define size of the network and host parts of
address
 Default mask
 is a 32 bit binary number written in dotteddecimal

defines the structure of an IP address
• Identifying the size of the network part of an IP
address
– Class A mask has a default mask of 255.0.0.0
– Class B default mask => 255.255.0.0
Network Layer
– Class C default mask => 255.255.255.0
4-4
A typical campus network
A
E
B
F
C
G
D
H
Network Layer
4-5
Subnets
 Main objective

Allow networks to be split into several parts
(subnets)
• For internal use and still act like a single network to
outside
 Idea

Some bits are taken away from the host number
• To create a subnet number

A third part appears in the middle of the address
Network Layer
4-6
Subnets: example
 The main router uses a subnet mask
 Indicating the split between
• network + subnet and host

The subnet mask in this case
is 255.255.252.0
• alternative notation is /22 indicating a 22 bit long mask

Outside the network, subnetting is not visible
Network Layer
4-7
How IP packets are processed
at a router
 Without subnetting
 Each router has a routing table listing
• Some number of network IP addresses
– Telling how to get to distant networks
• Some number of local host IP addresses
– Telling how to get to local hosts
 With subnetting
 Router table is reduced furthermore
• By creating a three-level hierarchy (network, subnet, and
host)

A router on subnet k
• Knows how to get to all other subnets and to local hosts
• does not have to know details about hosts on other
subnets
Network Layer
4-8
Scaling the IP address for the
Internet
 In the early 1990s

It became apparent that Internet was growing
so fast
• That all IP addresses would be assigned by mid-1990s
– new organizations would be unable to connect to Internet
 Several solutions were developed
 That allowed the Internet to grow
• Without letting us run out of IP addresses
– Classless Interdomain Routing (CIDR)
– Network Address Translation (NAT)
Network Layer
4-9
IP Addressing
 IP address: 32-bit
identifier for host,
router interface
 interface: connection
between host/router
and physical link



router’s typically have
multiple interfaces
host typically has one
interface
IP addresses
associated with each
interface
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
223.1.3.1
223.1.1.1 = 11011111 00000001 00000001 00000001
223
1
1
1
Network Layer 4-10
Subnets
 IP address:
 subnet part (high
order bits)
 host part (low order
bits)
 What’s a subnet ?
 device interfaces with
same subnet part of IP
address
 can physically reach
each other without
intervening router
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
subnet
223.1.3.1
223.1.3.2
network consisting of 3 subnets
Network Layer
4-11
Subnets
Recipe
 To determine the
subnets, detach each
interface from its
host or router,
creating islands of
isolated networks.
Each isolated network
is called a subnet.
223.1.1.0/24
223.1.2.0/24
223.1.3.0/24
Subnet mask: /24
Network Layer 4-12
Subnets
223.1.1.2
How many?
223.1.1.1
223.1.1.4
223.1.1.3
223.1.9.2
223.1.7.0
223.1.9.1
223.1.7.1
223.1.8.1
223.1.8.0
223.1.2.6
223.1.2.1
223.1.3.27
223.1.2.2
223.1.3.1
223.1.3.2
Network Layer 4-13
IP addressing: CIDR
CIDR: Classless InterDomain Routing
subnet portion of address of arbitrary length
 address format: a.b.c.d/x, where x is # bits in
subnet portion of address

subnet
part
host
part
11001000 00010111 00010000 00000000
200.23.16.0/23
Network Layer 4-14
Exercises
 You have a class C network, and you need
to design it for 7 usable subnets with
each subnet handling a minimum of 18
hosts each. Which of the following
network masks should you use?





255.255.224.0
255.255..255.230
255.255.255.224
255.255.255.240
None of the above
Network Layer 4-15
Exercises
 If a host on a network has the address
172.16.210.0/22, what is the address of
the subnetwork to which the host
belongs?





172.16.42.0
172.16.107.0
172.16.208.0
172.16.255.208
172.16.254.0
Network Layer 4-16
IP Addressing
 IP address: 32-bit
identifier for host,
router interface
 interface: connection
between host/router
and physical link



router’s typically have
multiple interfaces
host typically has one
interface
IP addresses
associated with each
interface
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
223.1.3.2
223.1.3.1
223.1.1.1 = 11011111 00000001 00000001 00000001
223
1
1
1
Network Layer 4-17
Subnets
 IP address:
 subnet part (high
order bits)
 host part (low order
bits)
 What’s a subnet ?
 device interfaces with
same subnet part of IP
address
 can physically reach
each other without
intervening router
223.1.1.1
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
subnet
223.1.3.1
223.1.3.2
network consisting of 3 subnets
Network Layer 4-18
Subnets
Recipe
 To determine the
subnets, detach each
interface from its
host or router,
creating islands of
isolated networks.
Each isolated network
is called a subnet.
223.1.1.0/24
223.1.2.0/24
223.1.3.0/24
Subnet mask: /24
Network Layer 4-19
IP addressing: CIDR
CIDR: Classless InterDomain Routing
subnet portion of address of arbitrary length
 address format: a.b.c.d/x, where x is # bits in
subnet portion of address

subnet
part
host
part
11001000 00010111 00010000 00000000
200.23.16.0/23
Network Layer 4-20
IP addresses: how to get one?
Q: How does network get subnet part of IP
addr?
A: gets allocated portion of its provider ISP’s
address space
ISP's block
11001000 00010111 00010000 00000000
200.23.16.0/20
Organization 0
Organization 1
Organization 2
...
11001000 00010111 00010000 00000000
11001000 00010111 00010010 00000000
11001000 00010111 00010100 00000000
…..
….
200.23.16.0/23
200.23.18.0/23
200.23.20.0/23
….
Organization 7
11001000 00010111 00011110 00000000
200.23.30.0/23
Network Layer 4-21
CDR – Classless InterDomain
Routing
A set of IP address assignments.
5-59
Network Layer 4-22
CIDR (ctd)
 Routing tables:

Address
• C: 11000010 00011…
• E: 194.24.00001…
• O: 194.24.0001…
Mask
255.255.11111000.0
255.255.11111100.0
255.255.11110…..
 A packet addressed to 194.24.17.4
 Matches the Oxford base
 A router
 with a single line for all 3 universities =>
• Three entries may be combined: 194.24.0.0/19
Network Layer 4-23