Protocol field: A protocol field is an 8-bit field that contains data about what transport layer protocol is being used
Protocol: A defined set of standards that computers must follow in order to communicate properly is called a protocol
Proxy service: A server that acts on behalf of a client in order to access another service
PSH flag: One of the TCP control flags. PSH is short for push. This flag means that the transmitting device wants the receiving device to push currently- buffered data to the application on the receiving end as soon as possible
Q
Quad A (AAAA) record: It is very similar to an A record except that it returns in IPv6 address instead of an IPv4 address
R
Recursive name servers: Servers that perform full DNS resolution requests
Reverse lookup zone files: They let DNS resolvers ask for an IP, and get the FQDN associated with it returned
Reverse proxy: A service that might appear to be a single server to external clients, but actually represents many servers living behind it
Round robin: It is a concept that involves iterating over a list of items one by one in an orderly fashion
Router: A device that knows how to forward data between independent networks
Routing protocols: Special protocols the routers use to speak to each other in order to share what information they might have
RST flag: One of the TCP control flags. RST is short for reset. This flag means that one of the sides in a TCP connection hasn't been able to properly recover from a series of missing or malformed segments
S
Sequence number: A 32-bit number that's used to keep track of where in a sequence of TCP segments this one is expected to be
Server or Service: A program running on a computer waiting to be asked for data
Server: A device that provides data to another device that is requesting that data, also known as a client
