Data packets are the data units transmitted in TCP/IP protocol communication. Aren’t “frames” the units transmitted within a local area network?
However, TCP/IP operates at Layer 3 (Network Layer) and Layer 4 (Transport Layer) of the OSI model, while frames operate at Layer 2 (Data Link Layer).
The content of an upper layer is transported by the content of a lower layer, so in a LAN, “packets” are contained within “frames.”
1. Packet Filtering, sometimes called static packet filtering, controls access to a network by analyzing incoming and outgoing packets and passing or blocking them based on predefined criteria. When a router forwards or rejects packets according to filtering rules, it acts as a packet filter.
When a packet arrives at a packet-filtering router, the router extracts specific information from the packet header and decides, based on filtering rules, whether the packet should be allowed through or discarded. Packet filtering works at the Network Layer of the Open Systems Interconnection (OSI) model, or the Internet Layer of TCP/IP.
2. As Layer 3 devices, packet-filtering routers use rules based on source and destination IP addresses, source and destination ports, and the packet’s protocol to decide whether to permit or deny traffic. These rules are defined using Access Control Lists (ACLs).
3. As you may recall, an ACL is a sequential list of permit or deny statements applied to IP addresses or upper-layer protocols. The ACL extracts the following information from the packet header, tests it against its rules, and then decides to “permit” or “deny.”
4. Simply put, when you browse a webpage, this simple action involves you first sending a data packet to a website. After receiving it, the website returns webpage data packets to you based on your data packet’s IP address. In other words, web browsing is essentially the exchange of data packets.
1. The Data Link Layer imposes a limit on the length of a data frame, which is the maximum data length the link layer can handle. This value is called the Maximum Transmission Unit, or MTU. For Ethernet, this value is typically 1500 bytes.
2. For IP packets, there is also a length field, described by 16 bits in the IP packet header. An IP packet can be up to 65535 bytes long.
3. Combining these two concepts leads to the first important conclusion: if the size of an IP packet exceeds the MTU value, fragmentation is required, meaning one IP packet is divided into multiple smaller ones.
The structure of a data packet is very similar to how