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A talk for the Harrow Computer Club on computer networking.

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  1. 1. Networking or the Alphabet Soup <ul><ul><li>Harrow Computer Club – Wed, 9 Feb 2011 </li></ul></ul><ul><ul><li>Bob Watson MA CMath MIMA MBCS </li></ul></ul>
  2. 2. Introduction <ul><li>Networking is complicated ... too complicated </li></ul><ul><li>Problems can occur in local PC hardware, modem/router, software, cabling, remote systems, ... </li></ul><ul><li>I am NOT going to teach you how to cure all possible network problems </li></ul><ul><li>I WILL try to explain some of the basics to give you a better understanding </li></ul>
  3. 3. The Alphabet Soup <ul><li>Probably more abbreviations than any other area of computing </li></ul><ul><li>Networks – LAN, WAN, WiFi, ADSL, ... </li></ul><ul><li>Protocols – TCP, IP, UDP, HTTP, FTP, POP3, SMTP, DNS, DHCP, ... </li></ul>
  4. 4. High-Level Protocols <ul><li>You have all heard of at least one of these </li></ul><ul><ul><li>HTTP – Hyper-Text Transfer Protocol </li></ul></ul><ul><ul><li>FTP – File Transfer Protocol </li></ul></ul><ul><li>These are </li></ul><ul><ul><li>“ high-level” protocols </li></ul></ul><ul><ul><li>visible to end-users (in Web URLs for example) </li></ul></ul><ul><li>They rely on and make use of several lower level protocols </li></ul>
  5. 5. Internet Protocol Suite <ul><li>Application Layer: </li></ul><ul><ul><li>BGP  · DHCP  · DNS  · FTP  · HTTP  · IMAP  · IRC  · LDAP  · MGCP  · NNTP  · NTP  · POP  · RIP  · RPC  · RTP  · SIP  · SMTP  · SNMP  · SSH  · Telnet  · TLS/SSL  · XMPP  · (more) </li></ul></ul><ul><li>Transport Layer: </li></ul><ul><ul><li>TCP  · UDP  · DCCP  · SCTP  · RSVP  · ECN  · (more) </li></ul></ul><ul><li>Internet Layer: </li></ul><ul><ul><li>IP (IPv4, IPv6)  · ICMP  · ICMPv6  · IGMP  · IPsec  · (more) </li></ul></ul><ul><li>Link Layer: </li></ul><ul><ul><li>ARP · NDP  · OSPF  · L2TP  · PPP  · Media Access Control (Ethernet, DSL, ISDN, FDDI)  · (more) </li></ul></ul>
  6. 6. Application Layer – HTTP, FTP, ... Transport Layer – TCP – Reliable Internet Layer – IP – Routing Link Layer – Ethernet etc – local
  7. 7. Network Addresses <ul><li>At the Link level, each network controller (NIC) has a physical address (MAC address) </li></ul><ul><li>But – only visible to other local systems </li></ul><ul><li>At the Internet level, each system has an IP address </li></ul><ul><li>These are visible globally and can be used to address a computer anywhere on the internet </li></ul><ul><li>(With some exceptions...) </li></ul>
  8. 8. IP Addresses <ul><li>32-bits – usually shown as 4 x 8-bits </li></ul><ul><ul><li>Google = </li></ul></ul><ul><ul><li>Microsoft = </li></ul></ul><ul><li>Difficult to remember </li></ul>
  9. 9. DNS – Domain Name System <ul><li>Hosts assigned structured names: </li></ul><ul><ul><li> </li></ul></ul><ul><ul><li> </li></ul></ul><ul><li>Each system has a name that can be looked up by DNS and translated to an IP address </li></ul><ul><li>Hierarchical, distributed system </li></ul>
  10. 10. DNS resolution <ul><li>3 requests to resolve one query – very expensive </li></ul><ul><li>Your PC won’t talk direct to these nameservers, it will go via a nameserver at your ISP </li></ul><ul><li>Every step in the chain caches recent results </li></ul>
  11. 11. Subnets <ul><li>The universe of IP addresses is sub-divided into ranges of various sizes </li></ul><ul><li>Each company that wants to run its own network is assigned one (or more) of those ranges </li></ul><ul><li>Eg: </li></ul><ul><ul><li>Google: – </li></ul></ul><ul><ul><li> – </li></ul></ul>
  12. 12. Subnet Masks <ul><li>Each separate range of IP addresses is called a “subnet” identified by base address and mask </li></ul><ul><li>Eg: – </li></ul><ul><ul><li>Base address = </li></ul></ul><ul><ul><li>Mask = (FF.FF.00.00 in hex) </li></ul></ul><ul><li>Or: – </li></ul><ul><ul><li>Base address = </li></ul></ul><ul><ul><li>Mask = (FF.FF.FF.00 in hex) </li></ul></ul>
  13. 13. Private Subnets <ul><li>Some IP address ranges are reserved for special uses </li></ul><ul><li>192.168.x.x = private networks, non-routable </li></ul><ul><li>Your PC probably has an address in this range </li></ul><ul><li>Private to the local LAN </li></ul><ul><li>Cannot be addressed from outside </li></ul><ul><li>Multiple private LANs can use the same addresses safely </li></ul>
  14. 14. Gateways <ul><li>Machines in one subnet can communicate with each other directly </li></ul><ul><li>To talk to a system in a different subnet you need a “gateway” to forward messages </li></ul><ul><li>Your broadband router does this job </li></ul>
  15. 15. DHCP – Dynamic Host Configuration <ul><li>IP addresses can be assigned statically but need good admin system </li></ul><ul><li>Can be assigned automatically using DHCP </li></ul><ul><li>Your router probably acts as a DHCP server </li></ul><ul><li>When your PC boots it broadcasts a message on the local LAN requesting an address </li></ul><ul><li>The router responds with address, subnet mask, gateway, DNS server address, etc... </li></ul>
  16. 16. Servers and Port Numbers <ul><li>An IP address identifies a host but how do you address a particular service on a host? </li></ul><ul><li>For example, one machine may be running a web server (HTTP), an FTP server and an Email server (POP3, SMTP) </li></ul><ul><li>High level protocols use Port Numbers </li></ul><ul><li>Eg: HTTP is usually on port 80 </li></ul>
  17. 17. Common Port Numbers Protocol Port Name FTP 21 File Transfer Protocol Telnet 23 Terminal connection SMTP 25 Simple Mail Transfer Protocol HTTP 80 HyperText Transfer Protocol POP3 110 Post Office Protocol
  18. 18. Useful Tools <ul><li>Standard with Windows (since XP) </li></ul><ul><ul><li>ipconfig </li></ul></ul><ul><ul><li>netstat </li></ul></ul><ul><ul><li>ping </li></ul></ul><ul><ul><li>tracert </li></ul></ul><ul><li>Free from </li></ul><ul><ul><li>fing </li></ul></ul>