Function attach_dns_filter 

pub(crate) fn attach_dns_filter(
    socket: &Socket,
    sport: u16,
    dns_identifier: u8,
    is_ipv6: bool,
) -> Result<()>

Attach a filter to a raw UDP socket so the kernel only delivers DNS replies destined to sport whose DNS transaction ID carries our 6-bit identifier, dropping all other UDP traffic (e.g. the host’s own DNS resolution).

Arguments

• socket - the raw UDP socket to attach the filter to
• sport - the worker’s source port (DNS replies carry it as their dport)
• dns_identifier - the 6-bit DNS identifier encoded in outgoing queries
• is_ipv6 - whether this is an IPv6 socket