Day15

1
Day15

• IP Space/Setup

2
IP

• Suite of protocols
• TCP
• UDP
• ICMP
• GRE
• Gives us many benefits
• Routing of packets over internet
• Fragmentation/Reassembly of packets
• IP Address System
• Netmasks

3
What is a network address?

• In every range of IP addresses, 2 addresses are
  reserved for special purposes
• The lowest address in the range
• The Network Address
• This identifies the network
• Example
• 200.200.200.55 / 255.255.255.0 has a network
  address of 200.200.200.0
• The highest address in the range
• The Broadcast Address
• An address in the network which everyone listens
  to
• Example
• 200.200.200.55 / 255.255.255.0 has a broadcast
  address of 200.200.200.255

4
Unusable Addresses

• In every network, the upper and lower addresses
  in your range, cannot be assigned to a
  workstation.
• Broadcast Network addresses.
• Example
• 199.120.197.128 / 255.255.255.128
• You cannot use
• 199.120.197.128
• 199.120.197.255

5
So how many?

• How many COMPUTERS can you put into the network
• 10.2.3.64 /255.255.255.224 ?
• 255-224 32
• Hence, there are 32 IPs in that range
• Neither the first nor last can be used
• 10.2.3.64 network
• 10.2.3.95 broadcast
• First available 10.2.3.65
• Last available 10.2.3.94

6
Use of IP addresses

• Given a 32 bit IP address, there are
  4,294,967,296 possible IP addresses. (In theory)
• IP addresses are running out quickly
• Not all computers NEED an IP address.
• With a smart router, or firewall, you can save IP
  addresses by using Network Address Translation
• Servers still need unique IP addresses

7
Network Address Translation (NAT)

• Computers send traffic with one address
• NAT router converts connection to new address
  and forwards it on
• NAT router receives reply and converts back to
  original address

10.0.0.2
I
Computer
NAT Router
209.2.3.4
10.0.0.1
10.0.0.3
Computer
Router
10.0.0.4
Computer
123.2.3.4
Computer
8
What are private addresses?

• 3 ranges of addresses were defined as being
  private
• These addresses are specifically dropped by
  routers on the internet
• Millions of computers in the world can have the
  same private address, but they are not DIRECTLY
  connected to the internet, something (Firewall,
  Router) is translating their address to a real
  one.

9
The Private Addresses

• 10.0.0.0 - 10.255.255.255

• 192.168.0.0 - 192.168.255.255

• 172.16.0.0 - 172.31.255.255

10
Private Addresses

• Drawbacks
• Public servers need a routable address, which
  must be converted to a private address
• Less intuitive
• Problem with trusted office to office VPN.
• Each office must be using DIFFERENT private
  addresses, otherwise you will run into address
  conflicts.

• Benefits
• Economic
• Conserve registered IP addresses
• Convenient
• Wont have to renumber your internal network if
  you change ISP
• Some Security
• Since nobody can connect to them directly, they
  must go through a firewall. Thus you can control
  who can have access

11
Long term solution

• In the long run we need to change to using IP V6
• 128 bit addresses
• 340,282,366,920,938,463,463,374,607,431,768,211,45
  6 addresses
• 1 IP per 1/10 square inch earth
• Slow progress on adaptation
• Equipment/software replacement
• Some of the best parts already back ported to
  IPV4 (ipsec)

12
Configuring a workstation

• All workstations should be configured with
• IP address
• Must be unique in the world unless behind a NAT
  router
• Either way must be unique in LAN
• Netmask
• This tells your computer what other computers it
  can talk directly to on the LAN
• Default Gateway
• This tells your computer the IP address of a
  router to which it can send traffic that isnt
  for your lan
• DNS settings
• This allows your computer to find out the IP of
  machines on the internet by name.
• You may optionally have static routes and WINS
  settings also.

13
Auto Configuring Workstations

• You dont need to configure every workstation in
  your company by hand
• DHCP Dynamic Host Configuration Protocol can be
  used to do it for you
• Each client has to be set up for DHCP
• It is the default TCP/IP setting in all versions
  of Windows
• Your DHCP server should be configured to
  distribute
• IP addresses from a free range
• The default gateway address
• DNS WINS server information

14
Lets see our DHCP info

• In windows type
• Ipconfig /all
• Physical Address. . . . . . . . .
  00-02-2D-A6-01-FB
• Dhcp Enabled. . . . . . . . . . . Yes
• Autoconfiguration Enabled . . . . Yes
• IP Address. . . . . . . . . . . .
  10.0.1.10
• Subnet Mask . . . . . . . . . . .
  255.255.0.0
• Default Gateway . . . . . . . . .
  10.0.1.1
• DHCP Server . . . . . . . . . . .
  10.0.1.1
• DNS Servers . . . . . . . . . . .
  10.0.1.2
• Lease Obtained. . . . . . . . . .
  Saturday, September 30, 2004 123511 PM
• Lease Expires . . . . . . . . . .
  Tuesday, October 03, 2004 123511 PM

15
When to use/not use DHCP

• DHCP perfect for
• Mobile environments
• Laptops come and go, dont want to assign a
  permanent IP to a computer which youll only see
  every 2 months.
• Desktops in a corporation
• Saves you from having to keep track of which IPs
  youve assigned.
• Allows end users set up computers without network
  admin help
• Its bad for
• Servers
• You dont want a web server to change address,
  since DNS needs to track it

16
Static Routes

• Necessary if you have more than 1 router in
  network.
• Either the routers need to know how to get to
  each others networks
• Or the workstations need to know
• Route print
• Route add 10.0.0.0 mask 255.0.0.0 168.28.48.1
• Route delete 10.0.0.0 mask 255.0.0.0

17
Which route wins

• When a route table is read the most specific
  route wins
• Network Netmask GW
• 10.0.0.0 255.0.0.0 1.1.1.1
• 10.0.0.0 255.255.0.0 1.1.1.2
• 10.0.0.0 255.255.255.0 1.1.1.3
• 10.0.0.0 255.255.255.252 1.1.1.4
• 0.0.0.0 0.0.0.0 1.1.1.5
• If this is the routing table a packet to 10.0.0.1
  would be routed to 1.1.1.4 because it is the most
  specific route in the table.