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Introduction to Computer Networking
The document provides an introduction to computer networking, covering fundamental concepts such as networking definitions, history, and components like wired and wireless connections. It discusses protocols like DHCP, ARP, DNS, and routing methodologies such as BGP, along with the differences between TCP and UDP transmission protocols. Additionally, it highlights the importance of manageability and industry expectations for modern data centers and the future of computer networks.
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Overview of the course by Amit Saha, introduction to networking concepts, and recommended resources.
Definition of networking and computer networking, with a brief history of computer network technology.
Visual schematics of a computer network, including wired and wireless first hop connections and their challenges.
Detailed discussion on WiFi standards, access point connections, and the general concept of wireless networks.
Introduction to wired networks focusing on Ethernet standards and CSMA/CD protocols.
Mechanisms for obtaining IP addresses via DHCP, IP packet structure, and header formats.
Basics of routing and domain name services (DNS) for network communication.
ARP functions, how it maps IP addresses to MAC addresses, and the basics of Ethernet.
Functionality of NAT for managing IP addresses and network translation processes.
Overview of routing hierarchies, intra-domain and inter-domain routing protocols.
Introduction to transport layer protocols, difference between TCP and UDP.
Techniques for ensuring reliable connections, including congestion control and the TCP three-way handshake.
Transitioning from shared to switched Ethernet, STP, VLANs, and properties of modern data centers.
Expectations for data center management, cost impacts of downtime, and the future trends in networking.
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Introduction to Computer Networking
- 1. INTRODUCTION TO COMPUTER NETWORKING AmitSaha IIT Gandhinagar 13th, 14th March 2015
- 2. Ground Rules • Thereare no “silly” questions. Focus on “why” • Slides with have fundamental concepts • Search on the web for anything you don’t understand • Almost everything is explained reasonably well on the web • You can send questions to [email protected]
- 3. Books – notmandatory • Data and Computer Communications - William Stallings • Internetworking with TCP/IP Volume 1 Principles, Protocols, and Architecture - Douglas E. Comer
- 4. What is Networking? •networking – the exchange of information or services among individuals, groups, or institutions • computer networking – the exchange of information or services among computers
- 5. A Brief History •http://visual.ly/brief-history-computer-network-technology
- 6. Schematic of aComputer Network
- 7. The first hop– wired
- 8. The first hop– wireless
- 9. Wireless First Hop- Possibilities • WLAN/WiFi • Cellular
- 10. Layering – LetsBreak up the Problem TheoreticalPractical
- 11. Wireless First Hop– WiFi • IEEE 802.11 (a/b/g/n/…) standards • Infrastructure mode (common) or Ad hoc mode Ethernet Token Ring New 802.11n
- 12. Connecting to aWiFi Access Point • Scanning • Joining • Authentication • Association • The station feels as if it is “plugged” into a wired network
- 13. Communicating with aWiFi AP • Wireless is a half duplex channel – either speak or listen • Signal strength is inversely proportion to square of distance • Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA) • Fancy name for how humans talk • This is generally true of all wireless systems (including humans)
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- 15. Wireless First Hop– Cellular • Not covered in this course
- 16. Wired First Hop- Ethernet • IEEE 802.3 standard • If two ends of the Ethernet cable (e.g., RJ45) is electrically up, connection is up. • Some authentication steps are usually there but we will skip those
- 17. CSMA/CD • Carrier SenseMultiple Access / Collision Detect
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- 20. Getting an IPaddress • DHCP – DHCP clients get IP addresses and networking parameters from DHCP server • Based on BOOTP • DHCPv6 (for IPv6) is also available
- 21. DHCP Packets • Discovery •Offer (possibly multiple) • Request • Acknowledge • Renew • Release Why do we need an IP address?
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- 26. Got an IP!Hurray! • But now what? How do I “go to” some website? • IP is just an identity • Still need to “route” to somewhere
- 27. DNS – DomainName Service • We almost always try to reach a human readable name • But machines route based on IP addresses • There must be a mapping from names to IP addresses • But who is going to do this translation?
- 28. Default Gateway • Ifhost does not know how to route, who does it ask? • There must be a “goto” guy in the network
- 29. Routing table –Host ubuntu@ubuntu-VirtualBox:~/Projects/OpenStack/New/cinder$ route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface default 10.0.2.2 0.0.0.0 UG 0 0 0 eth0 10.0.2.0 * 255.255.255.0 U 1 0 0 eth0 • Routing table becomes very interesting in a core router • 50,000 to 1,00,000 routes (entries like the above table) • We will get to it later
- 30. Who could … •Be a host’s Domain Name Server • Be a host’s Default Gateway
- 31. Are we readyto send?
- 32. ARP – AddressResolution Protocol • What is the MAC address for a given IP? • ARP resolves network layer address to link layer address • Remember network layer is the same as routing layer. This is also known as Layer 3(L3) • Link Layer is Layer 2 (L2)
- 33. Ethernet – IEEE802.3b • Broadcast medium • These days mostly switched Ethernet (point-to-point) • These days mostly Ethernet II • No LLC
- 34. Finally! • We cannow send
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- 36. An Example • Wireshark– Download it, install it and then play around with it • Instructions are there on the web itself • Will give you a lot of detail about packets and layering
- 37. DNS – DomainName Service • Hierarchical way of managing name space • Managed by Internet Assigned Numbers Authority (IANA) • http://www.iana.org/domains/root/db
- 39. DNS – RootServers • <a-m>.root-servers.net – 13 hostnames, around 500 instances • Use anycast to reach “nearest” instance – BGP supports this • 12 of the 13 root servers A-M exist in multiple locations • 11 on multiple continents • Root server ‘h’ exists in two U.S. locations. • Root server ‘b’ exists in a single location in the Los Angeles Area • http://www.root-servers.org/
- 40. Subnetting • Routing toeach individual hosts does not scale • Addresses grouped into different classes
- 41. CIDR • Any “classsystem” is bad • IPv4 was running out of unique IP addresses • Hence IPv6 but… • Classless Inter Domain Routing • Network portion can be of any size • Addresses need to specify subnet mask as well
- 42.
- 43. NAT – NetworkAddress Translation
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- 45.
- 46. Routing Hierarchy • Internetis divided into Autonomous Systems (AS) • Managed by a single administrator • 16 bit AS Number (ASN)
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- 48. Intra-Domain Routing • Typicallyuses UDP • Distance Vector • RIP – Bellman – Ford Algorithm • Link State • OSPF – Dijkstra’s shortest path • ISIS – Dijkstra’s shortest path • Note: The fundamental concept here is Distance Vector and Link State as two types of algorithms, not that they are used for intra-domain routing
- 49. Inter-Domain Routing • BorderGateway Protocol (BGP) – BGP version 4 • Path – vector routing • Uses TCP • External BGP – eBGP • Internal BGP – iBGP • Not to be confused with intra-domain routing (though iBGP could do that ) • Used to send information from one “side” of network to another • Policy engineering
- 50. Inter – DomainRouting
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- 54. Transport Layer • Providesend-to-end connection • On top of the routing layer • Two types of transmissions • Unreliable – User Datagram Protocol (UDP) • Reliable – Transmission Control Protocol (TCP)
- 55. UDP • Best effort,connection-less • Just send as fast as possible • When is it okay? • Phone calls, gaming, etc. • Simple stuff like DNS
- 56. TCP • Connection oriented •Setup/teardown connection • Sends stream of bytes, not messages • Reliable and in-order delivery • Flow Control • Congestion Control • Analogous to how humans communicate
- 57. Basics of ReliableConnection • How do you make a transmission reliable? • What do you need to protect against?
- 58. Basics of ReliableConnection Data Ack Sender Receiver time
- 59.
- 60. TCP – ConnectionSetup • Three-Way Handshake
- 61. TCP Sliding Window •http://www2.rad.com/networks/2004/sliding_window/
- 62. TCP – Beinga Good Citizen • Congestion Control • MaxWindow = min(Congestion Window, Receiver Window) • Congestion Window start at 1 • Original TCP: Additive Increase, Multiplicative Decrease
- 63. Congestion Avoidance Behavior Time Congestion Window Packetloss + Timeout Grabbing back Bandwidth Cut Congestion Window and Rate
- 64. Evolution of TCP 19751980 1985 1990 1982 TCP & IP RFC 793 & 791 1974 TCP described by Vint Cerf and Bob Kahn In IEEE Trans Comm 1983 BSD Unix 4.2 supports TCP/IP 1984 Nagel’s algorithm to reduce overhead of small packets; predicts congestion collapse 1987 Karn’s algorithm to better estimate round-trip time 1986 Congestion collapse observed 1988 Van Jacobson’s algorithms congestion avoidance and congestion control (most implemented in 4.3BSD Tahoe) 1990 4.3BSD Reno fast retransmit delayed ACK’s 1975 Three-way handshake Raymond Tomlinson In SIGCOMM 75 Taken from Aditya Akella’s slides, Dept. of Computer Science, University of Wisconsin - Madison
- 65. TCP Through the1990s 1993 1994 1996 1994 ECN (Floyd) Explicit Congestion Notification 1993 TCP Vegas (Brakmo et al) real congestion avoidance 1994 T/TCP (Braden) Transaction TCP 1996 SACK TCP (Floyd et al) Selective Acknowledgement 1996 Hoe Improving TCP startup 1996 FACK TCP (Mathis et al) extension to SACK Taken from Aditya Akella’s slides, Dept. of Computer Science, University of Wisconsin - Madison
- 66.
- 67. Ethernet • Original Ethernetused hub – shared ethernet • These days – switched ethernet
- 68. Switched Ethernet • CSMA/ CD • What is collision now? How is it handled?
- 69. Switching Types • Storeand forward • Cut through
- 70. Switched Ethernet –Arbitrary Topology • Can cause loops • Unlike IP header, no TTL to prevent looping
- 71. STP – SpanningTree Protocol • Creates a “tree” that “spans” entire graph • Distributed implementation
- 72. STP – RootBridge
- 73. STP – RootPorts
- 74. STP – DesignatedPorts
- 75. STP – BlockedPorts
- 76. STP – LinkFailure
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- 81. STP Variants • RapidSTP – Converges faster than STP • VLAN STP – Each VLAN can have a different STP tree
- 82. Data Centers • Cloudcomputing – Making computing elastic • Software Defined Networking (SDN) • Universities are using data centers for compute resources • Pay-as-you-go pricing model • Power and Cooling most important
- 83. Data Centers –Network Properties • Large number of ports • Large number of L2 end points • Multiple VMs per port • Relatively fewer L3 end points • Prime importance - manageability
- 86. Example Equipment –Pictures/Prices • Go to websites such as www.cisco.com and www.juniper.net and look at their product portfolio • www.cisco.com has interactive 3D models • Search for prices on the web
- 87.
- 88. Industry Expectations • Averageloss $5600/minute $300K/hour • Zero planned downtime is fast becoming the norm • Can you think of anything similar?
- 89. The Future ofComputer Networks • Manageability • Monitoring • Trouble shooting • Automated Healing • More bandwidth • Energy efficiency • Faster way of implementing something – algorithms/algorithmics • OpenSource based – cheaper and “better” • Broadband access will become a fundamental right