IPSG does not take effect on an S series switch. What are the possible causes

If IPSG does not take effect on an S series switch (except the S1700), possible causes include the following:
1. A binding entry is incorrect.
a. A static binding table is created using the user-bind static command. If the binding entry of a valid host is not in the binding table, add the host's binding entry to the binding table. If the host's entry exists in the binding table, check whether the MAC address in the entry is the same as the host's MAC address. If the network card of the host is replaced, the MAC address in the entry may not be updated. Check whether the host's entry contains VLAN information. Only when the interface connected to this host has been added to the correct VLAN, the switch allows the packets from the host to pass.
b. A dynamic binding table is generated only when DHCP snooping is enabled, the interface connected to the DHCP server is configured as a trusted interface, and then the PC obtains a new IP address.

2. IPSG is not enabled in the specified interface or VLAN view.
After a binding table is generated, the IPSG function must be enabled in the interface or VLAN view using the ip source check user-bind enable command.
IPSG takes effect only on the interface or VLAN where it is enabled, and IPSG check is not performed on the interfaces or VLANs with IPSG disabled. Therefore, if IPSG does not take effect on an interface or in a VLAN, the IPSG function may not be enabled on this interface or in this VLAN.

3. IPSG is enabled in the VLAN to which the uplink interface belongs.
IPSG is enabled on the user-side interface, namely, the downlink interface. If IPSG is enabled on the uplink interface, the packets returned by the gateway may be discarded. As a result, user service is interrupted.
Solution: Disable IPSG in the VLAN to which the uplink interface belongs.

4. DHCP snooping is disabled or a DHCP snooping trusted interface is configured on the uplink interface or in the VLAN to which the uplink interface belongs.
If DHCP snooping if disabled on an interface using the dhcp snooping disable command, or if a DHCP snooping trusted interface is configured on the interface using the dhcp snooping trusted command, the IPSG function on the interface or in the VLAN to which the interface belongs does not take effect.

5. Hardware ACL resources are insufficient.
The hardware ACL resources are used by IPSG and other services. If the ACL resources are insufficient, IPSG cannot take effect.
For example, you can run the display dhcp static user-bind all verbose command to view the IPSG status corresponding to static binding entries. If the value of IPSG Status is ineffective, IPSG of this entry does not take effect. The possible cause is that hardware ACL resources are insufficient.

6. A QoS traffic policy conflicts with IPSG.
This situation may only occur in V1R6C05. When a QoS traffic policy conflicts with IPSG, the traffic behavior in the QoS traffic policy takes effect. In this situation, you need to modify service configurations.

Other related questions:
Description of IPSG of S series switches
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