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IP Information Available to a Stateless Firewall
network interface
whether the packet is incoming or outgoing
source and destination IP addresses
ICMP, UDP, or TCP protocol
possibly if the packet contains a fragment
possibly if source routed
possibly TOS
Notes:
The term packet refers to an Internet Protocol (IP) network message. The IP standard defines the structure of a message sent between two computers over the network. It's the name given to a single, discrete message or piece of information that is sent across an Ethernet network. Structurally, a packet contains an information header and a message body containing the data being transferred. The body of the IP packet - it's data - is all or a piece (a fragment) of a higher-level protocol message.
All IP packet headers contain the source and destination IP addresses and the type of IP protocol message (ICMP, UDP or TCP) this packet contains. Beyond this, a packet header contains slightly different fields depending on the protocol type. ICMP packets contain a type field identifying the control or status message, along with a second code field for defining the message more specifically . UDP and TCP packets contain source and destination service port numbers. TCP packets contain additional information about the state of the connection and unique identifiers for each packet indicating the packet sequencing.