Transcript PowerPoint - DePaul University

Journey to the Center of the
Internet
John Kristoff
[email protected]
+1 312 362-5878
DePaul University
Chicago, IL 60604
ISOC-Chicago 2001
John Kristoff - DePaul University
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Internet as a layered architecture
• Application layer
• Web, email
• Transport layer
• Reliability, flow control
• Internet layer
• Routing, global addressing
• Link layer
• Ethernet, PPP
• Physical layer
• Wires, radio, optical fiber
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Meet Ms. Dana Paquette
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She has a high-speed
Internet connection
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She's browsing the web
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She just clicked on a
web link
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Let's watch...
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Take me to www.isoc.org
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Web site clicked is www.isoc.org
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IP doesn't understand names
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We must convert this to an IP address
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TCP/IP software to DNS server:
•
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"What is the IP address of www.isoc.org?"
DNS server replies:
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"www.isoc.org = 206.131.249.182"
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Protocol stack, connect()!
•
•
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Create destination TCP/IP packet using:
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Destination host = 206.131.249.182
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Destination application = http (port 80)
Fill in source host information
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Source IP address
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Source application number
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Other info (we'll return to specifics later)
Send connection request
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TCP/IP sends packet to adapter
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Ethernet card encapsulates data
"
Could be wireless, FDDI, cable modem, etc.
"
TCP/IP packet goes into payload
"
Ethernet dest. address = gateway router
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Out the card, onto the wire...
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Bit by bit...
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Into the walls and ceilings...
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Through the patch panel...
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Onto the Ethernet switch...
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To the campus router...
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Peels off layer 2 info
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Router performs
lookup for IP dest.
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Forwards towards
destination network
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Decrements time to
live field
•
Re-computes IP
checksum
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And out the Internet router...
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To the Internet towards ISOC.org!
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IP ties everything together
•
IP carries data end-to-end across links
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Routers examine IP layer information
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They forward towards the destination
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Similar to the sorting process of postal service
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Identifies both a source and destination
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Unreliable - no guaranteed delivery!
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Primary role of IP: to move packets around
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The IP datagram
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The case for reliability
•
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Sometimes the network is offered more
packets than it can handle
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Can't queue forever
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Might prefer to drop packets rather than delay them
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Sender can easily re-send packets
Need a protocol to ensure reliability
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The case for TCP!
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Note: reliability is placed in the hands of end-points
•
We'll come back to this in a minute
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Congestion control and avoidance
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TCP increases transmission rate over time
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If TCP detects a packet loss it slows down
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Competing TCPs lead to fairness over time
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The TCP segment
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The end-to-end picture
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Dana to ISOC.org TCP/IP packet
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End-to-end principle
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Guiding principle of the Internet architecture
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Considers where to put intelligence
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Minimize functions and features within the
communcations system
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Need end-to-end functions anyway
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Argues against fate-sharing and network
statefulness
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Is the Internet broken?
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E2E is being violated as standard practice
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Network address translation (NAT)
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Firewalls
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Various middleboxes
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New applications are difficult to deploy
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IPv6 could shift move back towards E2E
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Architecture has probably changed forever
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...won't come all the way back
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Anything else wrong with the 'net?
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Security, security and security
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There will continue to be major issues here
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Internet is based on trust relationships
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Host security is hard, net security doesn't work
Routing table growth
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Not a critical problem, but causing some concern
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Increase in multi-homing casing table bloat
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What's new and exciting?
(or "the I finished too early slide")
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Wireless
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Interactive applications
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Voice and games
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IPv6
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DNS
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High-speed technologies and testbeds
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References
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http://www.reed.com/Papers/EndtoEnd.html
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http://www.ietf.org
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RFC 2775 Internet Transparency
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RFC 1958 Architectural Principles of the Internet
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http://www.nanog.org
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http://networks.depaul.edu
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http://condor.depaul.edu/~jkristof/
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