[GS-4210 Series] Why can’t IP phones and door phones register to an IP PBX through the switch suddenly?

The new firmware of the GS-4210 switch series enhances security level, such as GS-4210-24PL4C firmware v2.305b210419. Some security functions like DOS are enabled by default. Due to the security mechanism, some packets may be dropped or blocked. In order to solve this issue, it is recommended to go to the page of DOS Global Setting and disable "UDP Blat" function as shown below. 

*GS-4210 Series includes following models:

GS-4210-24T4S / GS-4210-24T4SR 

GS-4210-24P4C / GS-4210-24PL4C (V2)

GS-4210-24UP4C (V2)

GS-4210-16UP4C (V2)

GS-4210-16P4C (V2)

GS-4210-16P2S (V2)

GS-4210-24P2S (V3)

GS-4210-24T2S (V2)

GS-4210-16T2S (V2)

GS-4210-24HP2C

GS-4210-8HP2S

GS-4210-48P4S (V2)

GS-4210-8P2T2S (V2)

GS-4210-48T4S (V2)