014.01.56.5. In the filter table of iptables, three basic chains are mentioned: INPUT, OUTPUT, and FORWARD. Can you explain the role of each of these chains and how they relate to incoming, outgoing, and routed packets, respectively? Describe the packet-processing sequence for incoming packets from both network interfaces and local processes, as illustrated in the provided flowcharts.
INPUT chain is for incoming packets, OUTPUT for outgoing packets and FORWARD for routed packets respectively. If a new packet arrives, and is classified as "input" by kernel, input chains are activated, similar for output and forward. As in the flowchart, an incoming packet from network can be consumed by a user process and may not reach the FORWARD chain or the OUTPUT chain. Packets generated by user processes won't reach the INPUT or FORWARD chains.
In the filter table of iptables, three fundamental chains are identified: INPUT, OUTPUT, and FORWARD. Each of these chains plays a distinct role in handling incoming, outgoing, and routed packets, respectively.
INPUT Chain: This chain deals with incoming packets targeting the local system. When a new packet arrives and is classified as input by the kernel, the INPUT chain is activated.
OUTPUT Chain: Responsible for outgoing packets originating from the local system. When a user process generates a packet, it is subject to the rules defined in the OUTPUT chain.
FORWARD Chain: This chain manages packets that are routed through the system to another destination. It is activated for packets that are neither destined for the local system nor generated by it.
In the provided flowcharts, the sequence of processing for incoming packets from both network interfaces and local processes is illustrated. It's important to note that an incoming packet from the network may be consumed by a user process, bypassing the FORWARD and OUTPUT chains. Similarly, packets generated by user processes won't reach the INPUT or FORWARD chains. Understanding these chains and their roles is crucial for effective packet filtering and network security using iptables.
