1. WWW Architecture


2. Internet Technologies

3. Hypertext Transport Protocol (HTTP)
  • wRequest/Response protocol
  • wMethods: GET, POST, HEAD, w
  • HTTP is a stateless protocol
  • HTTPS:A secure version of HTTP :
    • wUses Secure Sockets Layer (SSL)/
      Transport Layer Security (TLS)
4. Proxy Server
  • nA server that sits between a client (running a browser) and the Internet
  • nImproves performance by caching commonly used Web pages
  • nCan filter requests to prevent users from accessing certain Web sites
w5. Firewall
  • nA server that sits between a network and the Internet to prevent unauthorized access to the network from the Internet
6. Network Protocol Stack

7. Internet Layer: Internet Protocol (IP)
  • wResponsible for getting packets from source to destination across multiple hopsww
  • IP address: 32 bit value usually written in dotted decimal notation as four 8-bit numbers (0 to 255); e.g.
8. Transport Layer
  • Uses the Sockets programming model
  • wPorts identify application
  • nWell-known ports identify standard services
    (e.g. HTTP uses port 80, SMTP uses port 25)
  • wTransmission Control Protocol (TCP)
  • nProvides reliable, connection-oriented byte stream
  • wUDP
  • nConnectionless, unreliable
9. Application Layer
  • wTelnet: Remote sessions
  • wFile Transfer Protocol (FTP)
  • wNetwork News Transfer Protocol (NNTP)
  • wSimple Network Management Protocol (SNMP)
  • wSimple Mail Transfer Protocol (SMTP)
  • wPost Office Protocol (POP3)
  • wInteractive Mail Access Protocol (IMAP)
10. Domain Name System (DNS)
  • wProvides user-friendly domain names,
  • wHierarchical name space with limited root names:
  • wDNS servers map domain names to IP addresses

11. IPv6:

  • An IPv6 address is four times larger than an IPv4 address.
  • Internet, the backbone routers have an efficient and hierarchical addressing and routing infrastructure that uses smaller routing tables.
  • The new fields in the IPv6 header define how traffic is handled and identified.
  • The support for IPSec is an IPv6 protocol suite requirement.

    Comparison of features in IPv4 and IPv6

    IPv4 IPv6
    Source and destination addresses are 32 bits (4 bytes) in length. Source and destination addresses are 128 bits (16 bytes) in length.
    IPsec support is optional. IPsec support is required.
    No identification of packet flow for QoS handling by routers is present within the IPv4 header. Packet flow identification for QoS handling by routers is included in the IPv6 header using the Flow Label field.
    Fragmentation is done by both routers and the sending host. Fragmentation is not done by routers, only by the sending host.
    Header includes a checksum. Header does not include a checksum.
    Header includes options. All optional data is moved to IPv6 extension headers.
    Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IPv4 address to a link layer address. ARP Request frames are replaced with multicast Neighbor Solicitation messages.
    Internet Group Management Protocol (IGMP) is used to manage local subnet group membership. IGMP is replaced with Multicast Listener Discovery (MLD) messages.
    ICMP Router Discovery is used to determine the IPv4 address of the best default gateway and is optional. ICMP Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages and is required.
    Broadcast addresses are used to send traffic to all nodes on a subnet. There are no IPv6 broadcast addresses. Instead, a link-local scope all-nodes multicast address is used.
    Must be configured either manually or through DHCP. Does not require manual configuration or DHCP.
    Uses host address (A) resource records in the Domain Name System (DNS) to map host names to IPv4 addresses. Uses host address (AAAA) resource records in the Domain Name System (DNS) to map host names to IPv6 addresses.
    Uses pointer (PTR) resource records in the IN-ADDR.ARPA DNS domain to map IPv4 addresses to host names. Uses pointer (PTR) resource records in the IP6.INT DNS domain to map IPv6 addresses to host names.
    Must support a 576-byte packet size (possibly fragmented). Must support a 1280-byte packet size (without fragmentation).
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