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Network Layer: Internet Protocol

* The Address Resolution Protocol (ARP) is a dynamic mapping method that finds a physical address, given an IP address.
* An ARP request is broadcast to all devices on the network.
* An ARP reply is unicast to the host requesting the mapping.
* IP is an unreliable connectionless protocol responsible for source-to-destination delivery.
* Packets in the IP layer are called datagrams.
* A datagram consists of a header (20 to 60 bytes) and data.
* The MTU is the maximum number of bytes that a data link protocol can excapsulate. MTUs vary from protocol to protocol.
* Fragmentation is the division of a datagram into smaller units to accommodate the MTU of a data link protocol.
* The fields in the IP header that relate to fragmentation are the identification number, the fragmentation flags, and the fragmentation offset.
* The Internet Control Message Protocol (ICMP) sends five types of error-reporting messages and four pairs of query messages to support the unreliable and connectionless Internet Protocol (IP).
* ICMP messages are encapsulated in IP datagrams.
* The destination-unreachable error message is sent to the source host when a datagram is undeliverable.
* The source-quench error message is sent in an effort to alleviate congestion.
* The time-exceeded message notifies a source host that (1) the time-to-live field has reached zero or (2) fragments of a message have not arrived in a set amount of time.
* The parameter-problem message notifies a host that there is a problem in the header field of a datagram.
* The redirection message is sent to make the routing table of a host more effective.
* The echo-request and echo-reply messages test the connectivity between two systems.
* The time-stamp-request and time-stamp-reply messages can determine the roundtrip time between two systems or the difference in time between two systems.
* The address-mask request and address-mask reply messages are used to obtain the subnet mask.
* The router-solicitation and router-advertisement messages allow hosts to update their routing tables.
* IPv6, the latest verstion of the Internet Protocol, has a 128-bit address space, a resource allocation, and increased security measures.
* IPv6 uses hexadecimal colon notation with abbreviation methods available.
* Three strategies used to make the transition from version 4 to version 6 are dual stack, tunneling, and header translation.