1 Some Snapshots Rocky K. C. Chang 8 September 2008

2 What is this course about?  Internet Protocol (IP) Addressing (identifiers) Encapsulation (“message” units) Routing and forwarding  Additional considerations Reliability and others (TCP) Congestion control (TCP and router-based mechanisms) Scale: two-layer of routing (BGP and OSPF), addressing aggregation, fast packet forwarding Autonomous systems: policy routing Security

3 What is this course about?  Other issues Protocol correctness vs. protocol performance Inter-layer interaction (Web and TCP) Design principles underlying these networking protocols Design philosophy for the Internet infrastructure

4 What do you think?  Is Internet working today?  Will Internet work tomorrow?  If not, what will be the consequences?  What is the Internet?

5 What is the Internet?  A set of growing networked elements providing connectivity and services.  No one knows exactly how the Internet looks like.  No one knows exactly where the boundary of the Internet is.  No one knows exactly how and how fast the Internet grows.  No one knows for sure that the Internet will continue to work tomorrow.

6 What is the Internet?  Internet is a network of networks (network integration).  Started off as an experimental packet- switched network Packet switching (vs. circuit switching and message switching) 4-node ARPANET BBN Create a logical network on top of different physical networks.

7 Internet protocols  Protocol: A formal description of message formats and the rules two computers must follow to exchange those messages.  Each protocol defines two interfaces: Service interface defines the operations that local objects can perform on the protocol. Peer interface defines the form and meaning of messages exchanged between protocol peers to implement the communication service.

8 Internet protocols Protocol entity Message format and interpretation Services Protocol entity Message format and interpretation Services

9 TCP/IP protocol suite  Internet protocol suite, or TCP/IP protocol suite TCP/IP becomes the de facto standard for open system networking less than ten years ago (replaced the OSI protocol). No one owns the TCP/IP technology  The Internet Architecture Board (IAB) (  The Internet Engineering Task Force (IETF) (  The Internet Corporation for Assigned Names and Numbers (ICANN) (

10 TCP/IP protocol suite  A four-layer model (hour-glass)  The hour-glass model is everywhere. … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n Application Transport Network Data-link

11 TCP/IP protocol suite  In real life,

12 Milestones

13 Recent developments  From file transfer, remote login, etc. to IP telephony, IP storage, IP TV, etc  From data networks to wireless / satellite / mobile /cable /optical / power networks  From tens of thousands of hosts to tens of millions of hosts  From bursty data traffic to QoS- sensitive traffic  From secure to insecure Internet

14 The internetworking problem  Problem: How to interconnect heterogeneous networks effectively?  Interconnect homogeneous networks directly, e.g., Multiple Ethernet LAN segments Multiple Fibre Channels Multiple Token Rings Two wireless LANs …  Switching / bridging LAN switches Transparent bridging, spanning tree algorithm and source routing

15 The internetworking problem  Interconnect heterogeneous networks directly, e.g., DIX Ethernet with IEEE Ethernet Ethernet with Token Ring Wired LAN with wireless LAN  Three problems with interconnection at data-link layer: Do not scale to the number of data-link technologies. Do not scale to the number of hosts (networks). Do not have a common addressing space.

16 The internetworking problem S2 S1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7S3H8

17 Scaling to data-link technologies  Conversion between frame structures.  Scalability problem as the number of data- link technologies supported increases, e.g., Ethernet FDDI PPP Token ring Frame conversion

18 Scaling to network size  A switched LAN is a “flat” network---A single broadcast frame reaches every LAN. VLAN can relieve this problem at the expense of managing VLAN membership.  Spanning tree protocol does not scale well to network size. Take a longer time for the protocol to converge. Take a longer time to respond to network state changes.

19 Uncommon MAC address spaces  Different structures and number of bits used in MAC address space  Each address in a data-link technology must be universally unique.

20 A layer-3 solution to internetworking R2 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7R3H8

21 IP: Scaling to data-link technologies Ethernet FDDI PPP Token ring IP Encapsulation and demultiplexing

22 IP: Scaling to network size  IP network uses hierarchies to achieve scalability.  There are at least three levels: A single IP host (csultra6.comp.polyu.edu.hk) A IP subnet (four subnets in comp.polyu.edu.hk) An autonomous system (polyu.edu.hk)

23 IP: Uncommon MAC address spaces  Create a logical (unicast) address space to identify network interfaces.  Classes A-C for unicast and class D for multicast: NetworkHost (a) NetworkHost (b) NetworkHost (c) (d) 1

24 Directly connected IP hosts IP ETH TCP H1 IP ETH TCP H2 FTP TCP IP Ethernet protocol

25 Indirectly connected IP hosts R1 ETH FDDI IP ETH TCP R2 FDDI ETH IP H1 IP ETH TCP H2 FTP TCP IP FDDI protocol

26 Encapsulation  Data is processed at each layer through the protocol stack, until it is sent as a stream of bits across the network.  Each layer adds information to the data by prepending headers (and sometimes trailers) to the data that it receives.  A lower-level protocol does not interpret the message it is given by some higher- level protocol.

27 Encapsulation IP ETH TCP FTP Appl. data TCP hdr Appl. dataTCP hdrIP hdr Appl. dataTCP hdrIP hdrEth. hdr user input Send out to the network interface

28 Demultiplexing Appl. data TCP hdr Appl. dataTCP hdrIP hdr Appl. dataTCP hdrIP hdrEth. hdr Received from the network interface Other nonIP network protocols UDP-based applications Other TCP-based application processes

29 Internet addresses and port numbers  Each network interface has at least one IP address.  Both TCP and UDP use 16-bit port numbers to identify applications.  Servers are normally known by their well- known port numbers, usually between 1 and  Client ports are referred to ephemeral ports, i.e., short lived, which use port numbers above 1023.

30 IP software at end hosts  The IP software mainly consists of modules for Application layer, such as DNS Transport layer: TCP, UDP Routing layer: IP, ICMP, and others. Data-link layer: MAC-IP-addresses binding IP addresses MAC addresessHost names DNS ARP RARP

31 An example  A HTTP client is running in m1.sun.com to connect to a HTTP server at  The DNS client at m1.sun.com first obtains the IP address of  The application data (HTTP+TCP) will then be encapsulated by an IP datagram with m1.sun.com

32 An example IP source address = IP destination address =  Now m1.sun.com needs to run ARP to obtain the MAC address of network interface to the LAN.  The IP datagram is then encapsulated in an Ethernet frame with MAC source address = that of m1.sun.com MAC destination address = that of

33 IP Software at routers  The software at routers is mainly used for routing and datagram forwarding.  Each router is running at least a “routing protocol” to construct a routing (or forwarding) table. Each entry in a routing table consists of IP destination address and the next-hop’s IP address.  Upon receiving a datagram, a router forwards it based on a set of forwarding rules and the routing table.

34 Network programming  Two most common network APIs: Sockets and X/Open Transport Interface (XTI), a slight modification of AT&T’s Transport Layer Interface (TLI).  The APIs allows programmers to easily make “connections” with another application process, without knowing how the underlying network operates.

35 Basic socket calls for a client socket connect recv send peer sockaddr_in{} obtain a socket establish a connection to the peer receive and send data

36 Basic socket calls for a server socket listen recv send peer sockaddr_in{} obtain a socket mark the socket as a listening socket receive and send data bind accept local sockaddr_in{} bind the server’s IP address and port to the socket accept new connections

37 10 choices that were critical to the Internet’s success

38 10 right choices (by Scott Bradner) 1. Make it all work on top of existing networks (about networks, not a network). 2. Use packets, not circuits. 3. Create a routing function. 4. Split TCP and IP. 5. The NSF funded the UC/Berkeley to put TCP/IP into the Unix OS. 6. CSNET connected with ARPANET ( only).

39 10 right choices (by Scott Bradner) 7. The NSF required users of the NSFNET to use TCP/IP. 8. Intl. telecomm standard bodies rejected TCP/IP, then created OSI. 9. The NSF created an “Acceptable Use Policy” restricting NSFNET use to noncommercial activities. 10. Once things started to build, government stayed mostly out of the way.

40 Exercises this week  Try out the following commands (with various options) and network diagnosis tools: ipconfig netstat arp ping (ICMP, UDP, TCP, HTTP) traceroute (tracert, pathping, ICMP/TCP/UDP, etc) wireshark

41 Acknowledgments  URL for the 10 choices people.org/archives/interesting- people/200209/msg00018.html