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CLI-based Configuration Guide - Security

AR500, AR510, AR531, AR550, AR1500, and AR2500 V200R010

This document provides the basic concepts, configuration procedures, and configuration examples in different application scenarios of the network management feature supported by the device.
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Packet Filtering Firewall

Packet Filtering Firewall

A packet filtering firewall uses access control lists (ACLs) to filter packets based on the upper-layer protocol ID, source and destination IP addresses, source and destination port numbers, and packet transmission direction.

When receiving an IP datagram, the firewall obtains the packet header, and then compares the packet header information with ACL rules to determine whether to forward or discard the IP datagram. Figure 5-2 shows how packet filtering is implemented on the firewall.

Figure 5-2  Packet filtering firewall

Packet Filtering Firewall on the Device

The device supports packet filtering firewall and can filter the following packets:
  • Common IP packets: The firewall checks the source and destination IP addresses, source and destination port numbers, and protocol IDs of IP packets against an ACL. It forwards the packets permitted by the ACL and discards the packets denied by the ACL. The information that the firewall checks is contained in the IP, TCP, or UDP header.
  • Fragment packets: The firewall can identify the packet types, including non-fragment packets, initial fragment packets, and non-initial fragment packets.

    When receiving the initial fragment of a packet, the firewall compares Layer 3 and Layer 4 information of the initial fragment with the ACL. If the fragment is permitted by the ACL, the firewall records information about this fragment and creates a matching table for the following fragments. When the following fragments arrive, the firewall directly forwards them according to the matching table.

    In addition, the firewall has a default method to process the packets that do not match the ACL. The default method can be set by users.

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Updated: 2019-05-20

Document ID: EDOC1100034236

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