Internet Protocol Addressing

1
Internet Protocol Addressing

• Basics of IP addresses
• Classes of IP Networks
• Subnet masks and introduction to subnetting

2
IP layer 3 - Addressing

• IP addresses are used to identify the source and
  destination of a packet
• IP addresses are logical, configured by software
• An IP address
• Is a 32-bit number that is assigned manually or
  dynamically (DHCP)
• Contains a network ID a host ID embedded within
  the 32-bit number
• Usually expressed using dotted decimal notation
• Physical address? OSI Layers 1 2 technologies
  (Ethernet, Token Ring) use physical addresses
• MAC address an unchangeable number that is
  burned into a network cards read only memory
  by the manufacturer
• ARP (address resolution protocol) is used to
  resolve an IP address into a physical address for
  a given local area network. Ultimately MAC
  addresses are used to identify hosts

3
Binary numbers

• Binary numbers - Two digits possible, 1 or 0
• In an 8 bit number the following shows how each 1
  digit would be interpreted

27 26 25 24 23 22 21 20
Decimal equivalent
128 64 32 16 8 4 2 1 255
4
High-Order Bit Patterns
27 26 25 24 23 22 21 20

• Binary Decimal
• 10000000 128
• 11000000 192
• 11100000 224
• 11110000 240
• 11111000 248
• 11111100 252
• 11111110 254
• 11111111 255

5
Low-Order Bit Patterns

• Binary Decimal Exponent
• 00000001 1 21 - 1
• 00000011 3 22 - 1
• 00000111 7 23 - 1
• 00001111 15 24 - 1
• 00011111 31 25 - 1
• 00111111 63 26 - 1
• 01111111 127 27 - 1
• 11111111 255 28 - 1

6
IP addresses

• Have 32 bits one long binary integer, for
  example
• 11000000101010001111111101100100
• Usually interpreted as 4, 8-bit numbers, each 8
  bit number is referred to as an octet
• Here is the IP address with periods between each
  octet
• 11000000 . 10101000 . 11111111 . 01100100
• Each 8 bit number is usually expressed in
  decimal, each decimal separated by a period (or
  dot)
• Referred to as Dotted decimal notation
• And finally, the same IP address in dotted
  decimal notation
• 192.168.255.100

7
How an IP address Is Composed
Part of the 32 Bits represents A network ID
The remainder is Used to represent A host with
the network
8
Network Host IDs

• Network ID Each network has a unique network
  number
• Each Network connected to the Internet has to
  have a globally unique ID no other
  Internet-connected network in the world can have
  the same Network ID
• Host ID
• Within a given network Host IDs are used to
  identify hosts
• Hosts any device that needs to be addressed by
  an IP address - computers, printers, routers,
  etc.
• Host IDs must be unique within a given network.

9
Classes of networks

• 3 basic classes of IP networks of most interest
  in MIS 424
• Class A, B, and C
• Class D is a special purpose class used for
  multi-casting
• Classes differ in how many octets are used to
  represent network ID
• In designing IP addressing, the intent was to
  efficiently use the address space to accommodate
  different types of networks
• A few very large networks class A
• A fair number of medium size networks class B
• A large number of small networks class C

10
How Bits Are Set Up for Each IP Address Class
Note This shows the binary values in the first
3 bits of the 3 classes 0?? For class A 10? For
class B 110 for class C
11
How Address Classes Affect a Network
Ranges of 1st octet network IDs
A
B
C
12
private address cannot be routed on the
internet
13
Network and Broadcast Addresses

• Network address identifies a network (apart
  from any hosts)
• Any IP address where all host bits are 0
• Broadcast address
• Address that all hosts on a network must read
  all host bits are 1
• Broadcast traffic
• Seldom forwarded from one physical network to
  another

14
IP Address Guidelines

• First Octet Network ID Rules
• Network ID cannot be 127.
• ID bits cannot be all 1s.
• ID bits cannot be all 0s.
• For class B or C Network IDs
• Second octet (and the third octet for class C
  networks) can be any number from 1 -255, or
  00000000 to 11111111
• Class B 131.0.x.x or 131.255.x.x are OK
• Class C 200.0.0.x or 200.255.255.x or
  200.255.0 are all OK

15
IP Address Guidelines

• Host ID must be unique within a network ID
• Host ID cannot be all ones or all zeros (all ones
  or zeros for an octet translates into decimal 0
  or decimal 255 for the octet)
• Class A 10.0.0.0 and 10.255.255.255 are not OK
• Class B 131.210.0.0 and 131.210.255.255 are not
  OK
• Class C 200.10.10.0 and 200.10.10.255 are not OK
• 10.0.0.0, 131.210.0.0 , and 200.10.10.0 are
  network IDs
• For class A B networks a specific octet could
  be all ones or zeros (but not all octets)
• Class A 10.0.0.5 and 10.10.255.0 are OK
• Class B 131.210.0.10 and 131.210.255.5 are OK
• IP address of client gateway is the router.
• Address class affects subnet mask value.

16
IP Networks, Subnets, And Masks

• Subnet mask
• Special bit pattern that blocks off the
  network portion of an IP address with an all-ones
  pattern
• Default masks for Classes A, B, and C
• Class Layout Default Mask
• Class A n h.h.h 255.0.0.0
• Class B n.n h.h 255.255.0.0
• Class C n.n.n h 255.255.255.0

17
Example of a Subnet Mask Used for a Class B IP
Address
This heading should read Bits used for a default
subnet mask
18
Use of a subnet mask

• For now, an octet in the mask will either be all
  ones or zeros
• decimal 0 or 255
• A 255 means use the number in this address
  octet
• A 0 means to not look at an octet of an IP
  address and replace it with a zero.
• The following shows how you can use a mask to
  transform an IP address into a modified number

19
Example of using a subnet mask for routing
Network 131.107.0.0 Mask 255.255.0.0
Network 200.10.10.0 Mask 255.255.255.0
200.10.10.100
131.107.0.100
131.107.0.101
200.10.10.101
20
Using a subnet mask for routing
Source host

• Suppose host 131.107.0.100 wants to send a packet
  to 131.107.0.101
• 1st, the host uses its subnet mask to determine
  its own network ID
• Then the host applies its mask to the destination
  address
• If these two numbers are the same, it indicates
  that the destination is on the same network as
  the source it doesnt need to be routed.

Destination host
21
Using a subnet mask for routing
Source host

• Suppose host 131.107.0.100 wants to send a packet
  to 200.10.10.100
• The host uses its subnet mask is used to
  determine its network ID
• Then the host applies its mask to the destination
  address
• If these two numbers are the different, it
  indicates that the destination is on a different
  network than the source it needs to be routed.

Destination host
22
Routing

• A basic purpose of the subnet mask is to make a
  binary decision is the destination local or not
• If the destination address is not local, it will
  send the packet to the router
• So, how does a host know where the router is?
• One way is through the default gateway the IP
  address of the router that a host will normally
  use
• Minimum pieces of IP configuration
• IP address
• Subnet mask
• IP address of the default gateway (if you want to
  send packets outside of the current network)

23
Problems with default masks

• They only provide for a single network segment
• Class C 255.255.255.0 allows for a maximum of
  254 hosts on the segment
• Class B 255.255.0.0 allows for a maximum of
  65,534 hosts on the segment
• Class C 255.0.0.0 allows for a maximum of
  16,777,214 hosts on the segment
• Beyond class C networks, current LAN technologies
  will not support anywhere near the maximum number
  of hosts/segment
• Since there is only 1 network segment
• Difficult to use different topologies in the LAN
  (Ethernet, FDDI, Token Ring)
• Difficult to have a geographically dispersed LAN
  connected using a WAN technology.

24
IP Subnets

• Subnetting
• Using bits from the host portion of an IP address
  to further subdivide an organizations network
• Use of a default mask can only identify the true
  class A, B or C network ID for a hosts own IP
  address.
• Additional bits to the right of the default mask
  are used to identify subnet IDs that are assigned
  by the organization
• the Class A, B or C network ID still exists, the
  extended network ID is used internally within an
  organizations network for routing
• Two basic approaches of subnetting
• Constant length subnet mask (CLSM) all subnets
  have the same subnet mask (our main emphasis
  here)
• Variable length subnet mask (VLSM) subnets can
  have different masks depending on the of hosts
  on each subnet

25
Subnetting

• A subnet is a physical segment that uses IP
  addresses derived from a single network ID
• Each subnet segment uses a the same network ID,
  but appends it with a unique subnet ID
• Subnetting offers several advantages.
• Allows you to mix different technologies such as
  Ethernet and Token Ring
• Allows you to overcome limitations of current
  technologies, such as number of hosts per segment
• Allows you to reduce network congestion by
  redirecting traffic and reducing broadcasts

26
A simple approach to subnetting

• A common approach is to use 1 or 2 whole octets
  of the host ID to represent a subnet ID
• Possible Class A masks with subnetting
• 255.255.0.0 254 subnets, 65,534 hosts/subnet
• 255.255.255.0 - 65,534 subnets, 254 hosts/subnet
• Possible Class B mask with subnetting
• 255.255.255.0 254 subnets, 254 hosts/subnet
• No subnetting possible with a Class C network

1st octet of a Class A address is the network ID
It remains fixed
1st 2 octets of a Class B address are the network
ID They remain fixed
27
Example of routing within a subnetted network
Network 131.210.2.0 Mask 255.255.255.0
Network 131.210.1.0 Mask 255.255.255.0
131.210.1.100
131.210.2.100
131.210.2.101
131.210.1.101
To the Internet
28
Example 1 Routing within a subnetted network
Source host

• Suppose host 131.210.1.100 wants to send a packet
  to 131.210.1.101
• 1st, the host uses its subnet mask to determine
  its own subnet ID
• Then the host applies its mask to the destination
  address
• If these two numbers are the same, it indicates
  that the destination is on the same subnet as the
  source it doesnt need to be routed.

Destination host
29
Example 2 Routing within a subnetted network
Source host

• Suppose host 131.210.1.100 wants to send a packet
  to 131.210.2.100
• The host uses its subnet mask is used to
  determine its subnet ID
• Then the host applies its mask to the destination
  address
• If these two numbers are different, it indicates
  that the destination is not on the same subnet as
  the source it needs to be routed

Destination host
30
Example 3 Routing within a subnetted network
Source host

• Suppose host 131.210.1.100 wants to send a packet
  to 60.5.10.100 (somewhere on the Internet)
• The host uses its subnet mask is used to
  determine its subnet ID
• Then the host applies its mask to the destination
  address
• If these two numbers are different, it indicates
  that the destination is not on the same subnet as
  the source it needs to be routed.
• The router sends it onto the Internet since its
  not a local subnet, its on a network of a
  different organization

Destination host