Routing And Switching Questions
The process of ACL (Access Control List) evaluation involves the following steps:
1. Packet arrival: When a packet arrives at a router or switch, it is checked against the configured ACLs.
2. Source IP address check: The source IP address of the packet is compared with the entries in the ACL. If there is a match, the evaluation proceeds to the next step. If there is no match, the packet is either dropped or forwarded based on the configured default action.
3. Protocol check: The protocol field of the packet is examined to determine if it matches any protocol entries in the ACL. If there is a match, the evaluation proceeds to the next step. If there is no match, the packet is either dropped or forwarded based on the configured default action.
4. Port check: If the packet is a TCP or UDP packet, the source and/or destination port numbers are checked against the corresponding entries in the ACL. If there is a match, the evaluation proceeds to the next step. If there is no match, the packet is either dropped or forwarded based on the configured default action.
5. Action taken: If the packet matches any ACL entry, the configured action associated with that entry is taken. This action can be either permit (allow the packet to continue its journey) or deny (drop the packet).
6. Evaluation order: ACLs are evaluated in a sequential order, starting from the top of the ACL list. Once a match is found, the evaluation stops, and the corresponding action is taken. Therefore, the order of ACL entries is crucial, as the first match determines the fate of the packet.
Overall, the process of ACL evaluation involves checking the source IP address, protocol, and port numbers of the packet against the configured ACL entries, and taking the appropriate action based on the match or non-match.