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Network Layer (Datagram networks (Datagram or VC network (Internet…

- - - - data exchange among computers
      - “smart” end systems (computers)
      - many link types
    - - evolved from telephony
      - human conversation
      - “dumb” end systems
- - - - IP Fragmentation & Reassembly
        
        network links have MTU (max.transfer size) - largest possible link-level frame.
        
        large IP datagram divided (“fragmented”) within net
      - IP Addressing
        
        IP address: 32-bit identifier for host, router interface
        
        interface: connection between host/router and physical link
        
        Subnets
        
        subnet part (high order bits)
        
        host part (low order bits)
        
        CIDR: Classless InterDomain Routing
        
        get IP address
        
        hard-coded by system admin in a file
        
        DHCP: Dynamic Host Configuration Protocol
        
        DHCP client-server scenario
        
        host：DHCP discover
        
        DHCP server：DHCP offer
        
        host：DHCP request
        
        DHCP server：DHCP ack
        
        get subnet part：Hierarchical addressing
        
        route aggregation：Fly-By-Night-ISP
        
        more specific routes：ISPs-R-Us
        
        get block
        
        ICANN: Internet Corporation for Assigned
        Names and Numbers
  - - - outgoing datagrams: replace
      - remember (in NAT translation table)
      - incoming datagrams: replace
    - - solution 1: statically configure NAT to forward incoming connection requests at given port to server
      - solution 2: Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol.
      - solution 3: relaying (used in Skype)
  - - - Priority
      - Flow Label
      - Next header
    - - Checksum
      - Options
      - ICMPv6
    - - Tunneling
- - - - Switching Via Memory
        
        First generation routers
      - Switching Via a Bus
        
        bus contention
      - Switching Via An Interconnection
        Network
      - Queuing
        
        Head-of-the-Line (HOL) blocking
- - - - ARP table: IP/MAC address mappings
      - Same LAN
      - routing to another LAN
- - - - Dijkstra’s algorithm
        
        forwarding table
        
        Algorithm complexity
        
        Oscillations possible:
    - - routes change slowly over time
    - - routes change more quickly