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 traffic matches the ACL rule. When the traffic behavior is deny, the system discards traffic matching the rule. When the traffic behavior is permit, the system forwards traffic matching the rule. 
2. When deny is used in the ACL rule, the system discards traffic matching the ACL rule regardless of the traffic behavior.
3. If an ACL does not contain rules, the traffic policy referencing the ACL does not take effect.

•  Telnet

1. When permit is used in the ACL rule:

– If the ACL is applied in the inbound direction, the device with the specified source IP address can access the local device.

– If the ACL is applied in the outbound direction, the local device can access the device with the specified source IP address.

2. When deny is used in the ACL 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.

3. 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 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 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 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.