IP Addressing Revision'

1
IP AddressingRevision.

• Chris Beaumont

2
Session Aims

• Calculate IP addresses using Subnet masks

3
The story so far

• Each computer has an address called a ? ? ?
  Address.
• Which OSI Layer is this?
• How does the device get the address?
• What devices join the computers together?

4
How do we expand a LAN?

• Is there a limit to the size of an Ethernet LAN?
• What is it?
• Why ?

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Internetworking
Network A
NetworkB
Layer 3 Address (Network Number , Node Number)
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Routable Protocols

• Layer 3 protocols have to deliver the packet from
  Source to destination across many intermediate
  networks
• Routable protocols,
• eg
• IP (Internet Protocol)
• IPX (Internet Packet Exchange) - Novell
  Proprietary protocol

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Internetworking
R4
Router1
R5
R2
R6
1
3
2
Network66
Router3
1
2
3
Network42
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IP version 4 Addresses

• 32 bit binary number
• four octets
• Written as four decimal numbers separated by a
  full stop or dot
• One per octet
• E.g. 172.16.0.60
• How much of this address is network and how much
  is node address depends on the actual address and
  on the subnet mask being used

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IP Address Construction
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IP Network (Segment) Address vs. Node(host)
Address
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Subnet Mask

• IP address contains Network and node address
• First X bits are Network, rest is node
• indicate the number of bits as follows
• e.g

110.234.9.202 / 12
01101110.11101010.000001001.11001010
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Subnet mask tells us the value of X

• Subnet mask has first X bits are 1, rest 0
• Usually written in dotted decimal
• E.g. IP address

01101110.11101010.000001001.11001010
Subnet Mask
11111111.11110000.000000000.00000000
As dotted decimal
255.240.0.0
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Subnet Masks further example
255.0.0.0
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(No Transcript)
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QQuestions on the Diagram

• How many networks are shown in this diagram?
• What does the IP address on Interface 1, 2 etc
  refer to?
• Suggest suitable IP addresses for PCs shown
• If PC 192.168.2.1 sends to 192.168.2.2 what
  happens?
• If PC 192.168.2.1 sends to 192.168.1.1 what
  happens?
• If PC 192.168.2.1 sends to 192.168.3.1 what
  happens?

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Exercise

• Work out the network address, host address and
  subnet mask of the following
• a) 192.168.3.15/24
• b) 10.24.130.16 /18
• c) 194.200.240.202/25
• What is the maximum decimal value of an IP
  address octet?

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IP Address Classes

• Subnet mask may split address anywhere
• Classful addresses (old system)
• Class A, B, C distributed amongst user
  organisations for use on Internet connected
  networks
• Class D used for multicasting
• Class E reserved for future use

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IPv4 Address Classes
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Problems with IPv4

• Running out of IP addresses
• particular problems with Classful addresses
• Wasted addresses
• Internet routing tables size problem
• Each network needs an entry
• Other issues
• Packet fragmentation / Quality of Service
  implementation

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Solutions

• Private addresses / NAT
• Eg following cant be used on Internet
• 192.168.0.0/16
• 172.16.0.0/12
• 10.0.0.0/8
• NAT on border of the LAN converts any private
  addresses to a public address ( vice versa).

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Solutions

• CIDR (Classless Internet Domain Routing)
• Subnetting not confined to the octet boundaries
• Eg organisation needing 500 public IP addresses
  can be allocated /23 network rather than class B
  (/16)

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Solutions IPv6

• IPng
• Replacement for IPv4
• Addressing
• 128 bits
• Written as 6 x 4byte hex, colon separated
• FF0E00A0B9023
• Note repeated zero suppression
• Direct mapping of IPv4 to IPv6 addresses
• a.b.c.d
• See loads on the web

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Routing and Subnetworking
NIC1
NIC3
NIC2
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Subnetting Example1

• Suppose an organisation has been allocated
  193.1.1.0/24
• It requires 6 subnets
• Largest subnet requires 25 nodes
• How many bits needed to determine the subnet
  number?
• What is the subnet mask?
• How many hosts can we have on each subnet?

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193.1.1.0/24
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Allocated IP Address
193 . 1 . 1 .
0 /24 11000001.00000001.00000001.0000000
0
6 subnets requires 3 bits, thus
Subnet mask
255 . 255 . 255 .
224 /27 11111111.11111111.11111111.11100000
27
Subnet
193 . 1 . 1 .
0 /27 11000001.00000001.00000001.00000000

0
193 . 1 . 1 .
32 /27 11000001.00000001.00000001.0010000
0
1
Router
193 . 1 . 1 .
64 /27 11000001.00000001.00000001.0100000
0
3
193 . 1 . 1 .
128 /27 11000001.00000001.00000001.10000000

4
193 . 1 . 1 .
160 /27 11000001.00000001.00000001.10100000

5
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Subnet 1 addresses
193 . 1 . 1 .
32 /27 11000001.00000001.00000001.0010000
0
Router
193.1.1.33
193.1.1.36
193 . 1 . 1 .
34 11000001.00000001.00000001.00100010

193 . 1 . 1 .
35 11000001.00000001.00000001.00100011

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Exercise

• Suppose there are 8 x PCs on Subnet 4.
• Work out all the addresses needed for that
  subnet.
• Does a switch have an IP address?
• Does a router have an IP address?

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1. How many NICs in the Firewall?2. How many
subnets?3. What subnet mask?4. Allocate IP
Addresses
129.25.32.0 /24
Internet
Switch
Firewall
Border Router
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Summary

• Internetworking requires routable protocols
  (Layer 3)
• Address in 2 parts (Network / host)
• Subnet Mask determines split
• Calculate Subnets IP addresses