Linux kernel bonding driver hash algorithm Python equivalent for xmit_hash_policy=layer3+4 unfragmented TCP/UDP and IPv4

predict.py

import socket
import struct


def _ipv4_to_u32(ip_str: str) -> int:
    # network-order (big-endian) to host int
    return struct.unpack("!I", socket.inet_aton(ip_str))[0]


def bond_layer3_4_hash_tcp(
    src_ip: str,
    dst_ip: str,
    src_port: int,
    dst_port: int,
    slave_count: int
) -> int:
    """
    Predict the slave index for Linux bonding xmit_hash_policy=layer3+4 for
    unfragmented TCP.

    :param str src_ip: Source IPv4 address, e.g. "192.168.1.10"
    :param str dst_ip: Destination IPv4 address, e.g. "10.0.0.5"
    :param int src_port: TCP source port (0..65535)
    :param int dst_port: TCP destination port (0..65535)
    :param int slave_count: Number of slaves (>0)

    :return: Slave index in [0, slave_count-1]
    :rtype: int
    """
    if not (0 <= src_port <= 0xFFFF and 0 <= dst_port <= 0xFFFF):
        raise ValueError("Ports must be 0..65535")
    if slave_count <= 0:
        raise ValueError("slave_count must be > 0")

    sip = _ipv4_to_u32(src_ip)
    dip = _ipv4_to_u32(dst_ip)

    # Start with ports "as in the header".
    # A common interpretation is to pack them as 16|16 bits:
    h = ((src_port & 0xFFFF) << 16) | (dst_port & 0xFFFF)

    # Then XOR in the IPs (L3)
    h ^= sip ^ dip

    # Fold/mix as per docs
    h ^= (h >> 16)
    h ^= (h >> 8)

    # Bonding special-case for LAYER34: discard lowest bit
    h >>= 1

    # Reduce to slave index
    return h % slave_count


# Example usage
ip_src = '192.168.1.10'
ip_dst = '10.0.0.5'
slave_count = 2
port_dst = 80

# Show distribution of source ports to slave indices
distribution = [0] * slave_count
for port_src in range(1, 65536):
    slave_index = bond_layer3_4_hash_tcp(
        ip_src,
        ip_dst,
        port_src,
        port_dst,
        slave_count,
    )
    distribution[slave_index] += 1

print(f'Distribution of source ports to {slave_count} slaves:')
for idx, count in enumerate(distribution):
    print(f' Slave {idx}: {count} ports')