IP: The Internet Protocol

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IPThe Internet Protocol
Kevin BoldingElectrical EngineeringSeattle
Pacific University
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Internet Protocol

• IP is by far the most common networking protocol
• Used to connect thousands of local internetworks
  together

• IP is a network layer protocol, and is built on
  top of a data-link and physical layer protocol

Transport
TCP
UDP
IP
ICMP
Network
ARP
OSPF
RIP
ODI/NDIS
Data Link
NIC Driver
Physical
NIC/Media
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Datagrams

• Information to transmit may be anything from
  short messages to continuous streaming contents
• IP is a packet-switching network
• Maximum size of message that may be sent in one
  datagram
• Each datagram must be 64KB or less
• Long (or continuous) messages must be broken into
  many datagrams and sent separately
• Breaking messages into datagrams and reassembling
  them is the job of a Transport Layer Protocol
• TCP (Transmission Control Protocol) makes long
  messages appear continuous to the application
• UDP (User Datagram Protocol) provides less
  support, but is more lightweight and faster in
  some situations

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The Multi-Layer Process
Reading a web page at facebook.com using a browser
1. Browser asks TCP to open a connection with
www.facebook.com,assigns a TCP session number
(ex 1432)
2. facebook.com asks TCP to send the web page
data using session 1432
3. fackbook.coms TCP sends components using
datagrams in IP, eachtagged with session number
1432 Components lt 64KB each take one
datagram Components gt 64KB are split into
multiple datagrams
4. IP passes the data through the network using
routers
5. Your computers TCP client receives packets
and reassembles them
6. Web page contents are delivered to your browser
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IPv4 Header
Total Length (bytes)
Source Address
Identification
Type of Service
Destination Address
32 bits
Fragment Offset
Version
HeaderLength
Header Checksum
Options Padding
Flags
Time to Live
Protocol
20 bytes minimum
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IPv4 Addressing
1-254
1-254
1-254
1-254

• Each IP address is 32 bits long
• 4 groups of 8 bits
• Each group can have numbers 1-254
• 0 and 255 are reserved for broadcast

• Groups to the left specify the network, others
  the host
• Network address is assigned by InterNIC

• Class A Network.host.host.host
• Network is from 1-126, allows up to 16,000,000
  hosts

• Class B Network.network.host.host
• Network begins with 128 to 191, allows up to
  64,000 hosts

• Class C Network.network.network.host
• Network begins with 192-223, allows up to 254
  hosts

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The IP problem

• Were running out of IP addresses
• Solution A Bigger IP - 128-bit address (IPv6)
• In the meantime
• 32 bits - 4 billion addresses ought to do

• Squeezing the most out of the bits
• Private networks can have duplicate addresses
• 10.x.x.x, 172.16.x.x to 172.31.x.x, 192.168.0.x
  to 192.168.255.x

• Classless Inter-Domain Routing (CIDR)
• Forget classes, allow the number of network bits
  to be assigned as desired (ex 129.32.56.222/18
  is between B and C size)

• Dynamic Host Configuration Protocol (DHCP)
• DHCP server maintains a list of available IP
  addresses
• Computers request IP address from DHCP server
• IP address is leased for a fixed amount of time
  recycled

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IPv6 Header
Flow Label
Source Address 128-bit
Payload Length
Note Land area of earth 247 m2 --gt 281 1024
addresses/m2
Traffic Class
32 bits
Version
Destination Address 128-bit
Next Header
Hop Limit
40 bytes minimum
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Interface to Lower Layers

• What does an Ethernet (or other Data-Link Layer
  network) do with an IP message?
• Ethernet uses MAC addresses for routing
• IP address is nice, but useless

• ARP - Address Resolution Protocol
• Router/Host broadcasts an ARP Request
• Contains the IP address of desired destination
• Host with matching IP address responds
• ARP Reply broadcasts MAC address

• Caching
• Routers generally cache IP-to-MAC translations
• Need to refresh every now and then

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IP Summary

• Network-layer protocol
• Used from LANs to The Internet
• Routers are the key

• Still going strong
• Basic form (IPv4) has been given new life
• CIDR, private networks
• DHCP allows it to work with rapidly changing
  networks (I.e. laptops)

• The future
• IPv6 is coming
• Bigger addresses, better addresses