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Agenda

Agenda. Internet Address Pair IP Address Port Address Network Address Translation (NAT) Domain Name. Internet Address. Part I Two Parts. 2=1. IP Address 0.0.0.0 255.255.255.255 Port 0-64 k The full Internet Address pair <IP>:<Port> 10.10.125.5:80 Type in your web browser (demo).

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Agenda

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  1. Agenda • Internet Address Pair • IP Address • Port Address • Network Address Translation (NAT) • Domain Name

  2. Internet Address Part I Two Parts

  3. 2=1 • IP Address • 0.0.0.0 • 255.255.255.255 • Port • 0-64 k • The full Internet Address pair • <IP>:<Port> • 10.10.125.5:80 • Type in your web browser (demo)

  4. IP Address P.O.er There

  5. IP AddressSize & Form • IPv4 – Current Standard - Legacy • 32 bits total • 8 bit sections (base10 = 0-255) • 255.255.255.255 • IPv6 – Emerging Standard • 128 bits total (4 x IPv4) • 16 bit sections (hex = 0-FFFF) • FFFF:0000:FFFF:0000:FFFF:0000:FFFF:0000

  6. IP AddressFormatting • Convert IP address to network format • Inet_addr (char * stringFormat) • Returns: struct in_addr • Fails if not an IP address • Some confusing number completion intelligence • “125.126.4”  125.126.0.4 • “125.4”  125.0.0.4 • “125.126.12844”  125.126.128.44 • Inet_ntoa (struct in_addr) • Returns an ASCII string • htons (short HostOrderShort) • Returns the short in network byte order (i.e., swapped for Windows) • Example SOCKADDR_IN addr; addr.sin_family = AF_INET; addr.sin_addr.s_addr = inet_addr(“159.151.11.3”); addr.sin_port = htons(80);

  7. IP AddressPositional Meaning • 35.1.9.7 • Network Prefix • 35 • Subnet • 1 • 9 • Host • 7

  8. IP AddressingSpecial Addresses • 255.255.255.255 • INADDR_NONE == INADDR_BROADCAST • Must setup a DATAGRAM for limited broadcast • 0 • INADDR_ANY == ADDR_ANY • sin_addr.s_addr set to this before bind() so it assigns default. • 127.0.0.1 • INADDR_LOOPBACK • Send to self • *.*.*.{240-255} • Directed Broadcast to a specific subnet • *.*.*.{224-239} • Multicast group IP

  9. IP AddressingTypes of addresses • Unicast • Address assigned to an individual • Static • You assign your own (uncommon these days) • DHCP (Dynamic Host Configuration Protocol) • Server assigned address • APIPA (Automatic Private IP Addressing) • Used by routers servicing a single DHCP assigned address • Default if DHCP not available • This is NOT your MAC address on your NIC • Multicast • Address to a list of addresses • Temporary groups • Broadcast • Limited = everyone on your local net • Directed = send to a subnet

  10. Port Not your ordinary desert wine.

  11. PortsThe other half of the address • 16 bit number = 0 - 65,536 • Receiving Port • Must specify a specific port to listen on • Sending Port • Send on any available port (sockets decides) • Can specify send port, but may conflict

  12. PortsKnown & Not So Known • Well Known Ports • 0-1024 • Internet Assigned Number Authority (IANA) – The Registrar • Reserved for standard services (FTP, WWW, SMTP, Telnet, …) • Can use for anything (not recommended) • Often filtered by network hardware • IP address ignored and packet redirected to specific protocol server • Examples • HTTP = Port 80 (web server) • FTP = Port ? (check answer at www.iana.net) • Registered Port Numbers • 1024-65,536 • Not controlled by IANA • Some common services use 1024-10,000 • Be safe, stay high • Hippie Slogan or Good Advice? • 10k-64k

  13. Firewalls Keep Out!

  14. Types of Firewalls • Packet Filter • Proxies • Circuit Gateways

  15. NAT A baby Mosquito?

  16. Network Address Translation • What is it for? • Multiple NIC’s share the same IP Address • Who does this? • Routers at work/home sharing one IP Address • How does it do it? • Each NIC assigned an APIPA address • APIPA + Portα converted to Shared IP + Portβ • Router maintains the translation table and redirects incoming traffic accordingly.

  17. NAT in action Figure 1 Network Address Translation at work.

  18. NAT Traversal • Port Forwarding • Port always assigned to 1 computer • Port Triggering • Starting application temporarily forwards port • DMZ • All traffic also goes to specific computer • Determining WAN IP • From computer on the other side of router • IP Helper API, router config table

  19. Domain Name www.yahoo.com chuck.toonedin.com

  20. Domain Name ResolutionFacilities • Local Host Table (i.e. a cache) • <win>\SYSTEM32\DRIVERS\ETC\HOSTS (demo) • Fast, customizable • Doesn’t scale, gets out of synch with changes • Domain Name Service (DNS) Server • Off site server • Faster updates, hands off, scales • Slower, no control on updates, not always available • Propagation takes time (hrs – weeks) • Case Study • Use DNS if available • Store last used and defaults when not • Ping Demo • Plethora of other custom services • Network Information Service (unix) • NetBIOS over TCP/IP • Windows NLA: Network Location Awareness (mobile computing)

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