x86 assembly

section .text
    global _start

_start:
    ; Establish a connection to the local port
    mov dx, 1234h   ; Port number to connect
    mov cx, 2       ; Socket type: 2 for TCP

    mov ax, 0h      ; System call number: 0 for socket
    int 0x80        ; Call the kernel

    ; Save the socket file descriptor in ebx for later use
    mov ebx, eax

    ; Set up the firewall
    mov edx, 0h     ; Firewall control port
    mov al, 0FFh    ; Value to set for all bits

    out dx, al      ; Output the value to the control port

packet_loop:
    ; Read the incoming packet from the input port
    in al, dx

    cmp al, 10h     ; Compare the packet value with 0x10

    ; If the packet value is less than 0x10, allow the packet through
    ; by sending it to the output port
    jnc allow_packet

    ; If the packet value is greater than or equal to 0x10, block the packet
    ; and do not send it to the output port
    jmp block_packet

allow_packet:
    ; Send the packet value to the output port
    mov dx, 2h      ; Output port
    out dx, al

    ; Continue looping to process the next packet
    jmp packet_loop

block_packet:
    ; You can add code here to handle the blocked packet, e.g., log or drop it

    ; Continue looping to process the next packet
    jmp packet_loop

    ; Add more code here if necessary

    ; Clean up and exit the program
    mov eax, ebx    ; Socket file descriptor
    mov bx, 2       ; System call number: 2 for close
    int 0x80        ; Call the kernel

    mov eax, 1      ; System call number: 1 for exit
    xor ebx, ebx    ; Exit status: 0
    int 0x80        ; Call the kernel