How Are deny and permit in ACL Rules Used in Different Services?

The deny and permit parameters in ACL rules have different functions in different services.

• Traffic policy

  1. When permit is used in the ACL rule, the system executes the specified traffic behavior only when packets match the ACL rule. When the traffic behavior is deny, the system discards packets matching the rule. When the traffic behavior is permit, the system forwards packets matching the rule.

  2. When deny is used in the ACL rule, the system discards the packets matching the ACL rule regardless of the action defined the traffic behavior (except traffic statistics collection and traffic mirroring).

  3. If an ACL does not contain rules, the traffic policy using the ACL does not take effect.

• Simplified traffic policy

  1. When permit is used in the ACL rule, the system executes the behavior in the simplified traffic policy, for example, allowing the matching packets to pass and limiting the rate of matching packets.

  2. When deny is used in the ACL rule, the system discards the matching packets if the ACL is applied to the packet filtering function or executes the behavior in the simplified traffic policy if the ACL is applied to other functions.

  3. If an ACL does not contain rules, the simplified traffic policy using the ACL does not take effect.

• IPSec

  1. When permit is used in the ACL rule, the system uses IPSec policies to protect traffic matching the ACL rule, and then forwards the traffic.

  2. When deny is used in the ACL rule, the device rejects packets that match the ACL rule.

  3. When an ACL does not contain rules, the IPSec policy referencing the ACL does not take effect. That is, the system forwards the packets passing the interface without performing any operation.

• Firewall

  1. When permit is used in the ACL rule:

     • When the ACL is applied to the inbound traffic, the system forwards the packets matching the ACL rule sent from the low-priority zone to the high-priority zone.
     • When the ACL is applied to the outbound traffic, the system forwards the packets matching the ACL rule sent from the high-priority zone to the low-priority zone.

  2. When deny is used in the ACL rule:

     • When the ACL is applied to the inbound traffic, the system discards the packets matching the ACL rule sent from the low-priority zone to the high-priority zone.
     • When the ACL is applied to the outbound traffic, the system discards the packets matching the ACL rule sent from the high-priority zone to the low-priority zone.

  3. When an ACL does not contain rules:

     • When the ACL is applied to the inbound traffic, the ACL does not take effect, and the system discards all packets sent from the low-priority zone to the high-priority zone.
     • When the ACL is applied to the outbound traffic, the ACL does not take effect, and the system discards all packets sent from the high-priority zone to the low-priority zone.

• NAT

  1. When permit is used in the ACL rule, the system uses the address pool to translate addresses for the packets of which the source IP address is specified in the ACL rule.

  2. When deny is used in the ACL rule or the ACL does not contain rules, the NAT policy referencing the ACL does not take effect. That is, the system searches routes for packets, but does not translate addresses.

• Telnet

  1. When permit is used in the ACL rule:

     • If the ACL is applied in the inbound direction, other devices that match the ACL rule can access the local device.
     • If the ACL is applied in the outbound direction, the local device can access other devices that match the ACL rule.

  2. When deny is used in the ACL rule:

     • If the ACL is applied in the inbound direction, other devices that match the ACL rule cannot access the local device.
     • If the ACL is applied in the outbound direction, the local device cannot access other devices that match the ACL rule.

  3. When the ACL rule is configured but packets from other devices do not match the rule:

     • If the ACL is applied in the inbound direction, other devices cannot access the local device.
     • If the ACL is applied in the outbound direction, the local device cannot access other devices.

  4. When the ACL contains no rule:

     • If the ACL is applied in the inbound direction, any other devices can access the local device.
     • If the ACL is applied in the outbound direction, the local device can access any other devices.

• HTTP

  1. The device with the specified source IP address can establish an HTTP connection with the local device only when permit is used in the ACL rule.

  2. When deny is used in the ACL rule, other devices cannot establish HTTP connections with the local device.

  3. When the ACL rule is configured but packets from other devices do not match the rule, other devices cannot establish HTTP connections with the local device.

  4. When the ACL contains no rule, any other devices can establish HTTP connections with the local device.

• FTP

  1. The device with the specified source IP address can establish an FTP connection with the local device only when permit is used in the ACL rule.

  2. When deny is used in the ACL rule, other devices cannot establish FTP connections with the local device.

  3. When the ACL rule is configured but packets from other devices do not match the rule, other devices cannot establish FTP connections with the local device.

  4. When the ACL contains no rule, any other devices can establish FTP connections with the local device.

• TFTP

  1. The device with the specified source IP address can establish a TFTP connection with the local device only when permit is used in the ACL rule.

  2. When deny is used in the ACL rule, the local device cannot establish TFTP connections with other devices.

  3. When the ACL rule is configured but packets from other devices do not match the rule, other devices cannot establish TFTP connections with the local device.

  4. When the ACL contains no rule, the local device can establish TFTP connections with any other devices.

• SNMP

  1. When permit is used in the ACL rule, an NMS with a specified source IP address can access the local device.

  2. When deny is used in the ACL rule, the local device rejects access from other NMS.

  3. When the ACL does not contain rules, the local device access from any other NMS.

• NTP

  1. When permit is used in the ACL rule, the ntp-service access command takes effect.

  2. When deny is used in the ACL rule, the ntp-service access command does not take effect.

  3. When the ACL does not contain rules, the ntp-service access command does not take effect.