# 4. Network Layer

* Addressing
  * IPv4
    * IP address depletion&#x20;
    * Internet routing table expansion
    * Lack of end-to-end connectivity
  * IPv6&#x20;
    * Increased address space&#x20;
    * Improved packet handling&#x20;
    * Eliminates NAT&#x20;
    * Integrated security&#x20;
  * IP characteristics
    * Connectionless
    * Best Effort&#x20;
    * Media Independent&#x20;
* Routing
  * Directly-connected routes
  * Remote routes&#x20;
  * Default route&#x20;
* Default gateway
  * routes traffic from the local network to remote networks
* ICMPv4
  * ping
    * test connectivity
    * echo request, echo reply
  * Pinging the local loopback
  * Pinging the default gateway
  * Pinging the remote host
  * traceroute

Transport Layer

* End to End Connection
  * Port Number
    * Source Port
    * Destination Port
* Segmentation
* Reassembling
* Transmission Control Protocol (TCP)
  * Connection Oriented
    * Three-way handshake to establish connection
  * Sequence Number
    * Reordering
  * Reliable Delivery&#x20;
    * Retransmission
    * Time-out
  * Flow Control
    * Window Size
  * Application
    * HTTP, FTP, SMTP, Telnet
* User Datagram Protocol (UDP)
  * Connectionless
  * Unreliable Delivery
  * No Ordered Data Reconstruction
  * No Flow Control
  * Faster than TCP &#x20;
  * Application
    * DNS, SNMP, VoIP

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