Basics of Networking

1
Basics of Networking

• Thursday, September 16th, 2004
• Jason Parente
• IP
• TCP/UDP
• DHCP
• DNS
• WINS

2
IP
A
F
G
E
D
C
B
H
Router
Segment 2
Segment 1
3
IP

• Ethernet(MAC) Addresses
• MAC Media Access Control
• Every network card has an Ethernet address.
• My computers 00-0B-DB-42-13-26
• Problem MAC address cannot easily be easily
  be changed. They are hardcoded into the NIC
  (network interface card).

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IP

• IP Internet Protocol
• A 32-bit address. Example
• 11001010 00001111 10101010 000000001
• Dotted-Quad notation. Eg
• 202 15 170 1

5
IP

• IP Routing

A
F
G
E
D
C
B
H
Router
Segment 2
Segment 2
Segment 1
6
IP

• IP Routing

A
F
G
E
D
C
B
H
Router
Segment 2
Segment 2
Segment 1
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IP

• IP Routing
• 1- Packet must be routed if destination address
  is not in subnet.
• 2- If destination address is in subnet, send to
  that address.
• 3- If destination address is not in subnet, send
  to router address.

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IP

• Class A 132.x.y.z
• Class B 132.216.y.z
• Class C 132.216.68.z
• CTF has a class C network 132.216.68.x

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IP

• Reserved Addresses
• Loopback Class A ? 127.x.y.z
• Multicast Class A ? 224.x.y.z to 239.x.y.z
• Experimental Class A ? 240.x.y.z to
  255.x.y.z
• Intranets
• 10.0.0.0 10.255.255.255
• 172.16.0.0 172.31.255.255
• 192.168.0.0 192.168.255.255

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IP

• Reserved Addresses
• All the Internet 0.0.0.0 ? 0.x.y.z
• Network number 132.216.68.0
• IP Broadcast 132.216.68.255
• Default Router (Gateway) 132.216.68.1
• APIPA 169.254.0.1 ? 169.254.255.254

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IP

• One Subnet
• Subnet Mask 255.255.255.0
• Network number x.y.z.0
• Gateway x.y.z.1
• Broadcast Address x.y.z.255
• Total IP addresses 253

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IP

• Two Subnets
• Subnet Mask 255.255.255.128
• Network number x.y.z.0
• Gateway x.y.z.1
• Broadcast Address x.y.z.127
• Total IP addresses 125

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IP

• Two Subnets
• Subnet Mask 255.255.255.128
• Network number x.y.z.0 x.y.z.128
• Gateway x.y.z.1 x.y.z.129
• Broadcast Address x.y.z.127 x.y.z.255
• Total IP addresses 125 125

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IP

• Four Subnets
• Subnet Mask 255.255.255.192
• Eight Subnets
• Subnet Mask 255.255.255.224

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TCP UDP

• TCP Transmission Control Protocol
• UDP User Datagram Protocol

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TCP UDP

• UDP Process
• Send Packet A
• Send Packet B
• Packet B checksum invalid
• Re-Send Packet B
• Send Packet C (Lost)
• Send Packet D

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TCP UDP

• TCP
• Reliable
• Packet checksum
• Acknowledgement of received packets.

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TCP UDP

• TCP Process

Original Transmission
Re-transmit
ACK
Original Transmission 2
Sender
Receiver
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TCP UDP

• TCP Process
• Send Packet A
• Receive Acknowledgement(ACK) for A
• Send Packet B
• Wait for ACK for B
• Timeout exceeded -gt Re-send Packet B
• Receive ACK for B
• Send Packet C

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DHCP

• DHCP Dynamic Host Configuration Protocol
• System to dynamically and centrally loan IPs to
  machines.

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DHCP

• A server maintains a pool of available addresses.
• Clients request an IP and the server loans an IP
  to the machine for a set amount of time.
• If necessary, leases are renewed half-way through.

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DHCP

• The Process

DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPACK
DHCP Server
Client
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DNS

• DNS Domain Name System
• HOSTS Simple Name Systems

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DNS

• HOSTS
• ASCII text file that contains IP and Host name.
• Location
• \WINNT\System32\Drivers\ETC\hosts
• Example
• 132.216.68.5 nexus.sus.mcgill.ca
• 132.216.68.17 home.sus.mcgill.ca
• 132.216.68.17 tacos.sus.mcgill.ca

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DNS

• Tree architecture

mcgill.ca
campus.mcgill.ca
sus.mcgill.ca
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DNS

• Forward Name Resolution
• nexus.sus.mcgill.ca ? 132.216.68.5
• Reverse Name Resolution
• 132.216.68.5 ? nexus.sus.mcgill.ca
• Note The CTF reverse lookup zone is
• 68.216.132.in-addr.arpa

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DNS

• Common DNS Record Types
• A Records (Hosts)
• Simple forward pointer
• nexus.sus.mcgill.ca ? 132.216.68.5
• Start of Authority(SOA) Records
• Names the primary DNS for the domain
• E-mail address of administrator
• Useful for primary vs. secondary DNS servers.

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DNS

• Common DNS Record Types
• Name server/NS Records
• Define the Name servers in the domain.
• Ex
• sus.mcgill.ca NS nexus.sus.mcgill.ca
• CNAME Records(aliases)
• Use for more than one pointer to the same IP.
• EX
• Home ALIAS tacos.sus.mcgill.ca

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DNS

• Common DNS Record Types
• MX Records(Mail Exchange)
• Where to send jason_at_sus.mcgill.ca
• Note that there is a preference . Practical if
  more than one mail server exist.
• Pointer(PTR) Record or Reverse Host Record
• A PTR record is a reverse A record.

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WINS

• WINS Windows Internet Name Service
• Think of it as DNS for NT4 machines. Its legacy,
  and Windows specific.
• Uses Microsoft NetBios API.

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Resources

• Mastering Windows 2000 Server(Sybex - CTF)
• MCSA/MCSE Windows XP Professional Study Guide
  (Sybex - mine)
• Computer Networks A Systems Approach (Morgan
  Kaufmann - mine and crap)