mapdns appears to be IPv4-only: no AAAA synthesis and no IPv6-addressed mapdns handling

[SammyVimes]

Hi, thanks for hev-socks5-tunnel!

I think mapdns is currently (as of version 2.14.4) IPv4-only, even though the tunnel itself supports dual stack. This becomes a problem on IPv6-first / IPv6-only / NAT64 networks.

The tunnel itself seems to support IPv4/IPv6 dual stack, but mapdns appears to only support IPv4 synthetic mapping:

1. It only synthesizes A answers, not AAAA.
2. It only treats the mapped DNS endpoint as special when the destination address is IPv4.

Because of that, on ipv6-heavy networks, DNS/app flows may not work correctly through mapdns.

1. hev_mapped_dns_handle() only handles QTYPE=A

In src/hev-mapped-dns.c:

• it checks QTYPE == 1 and QCLASS == 1
• it writes an answer with:
  • type A
  • RDLENGTH = 4
  • a 32-bit mapped IPv4 address

So for an AAAA query, it does not create a mapping and returns a response with ANCOUNT = 0.

2. mapdns interception only triggers for ipv4 destination addresses

In src/hev-socks5-tunnel.c, udp_recv_handler():

if (dns && addr->type == IPADDR_TYPE_V4) {
    int faddr = hev_config_get_mapdns_address ();
    int fport = hev_config_get_mapdns_port ();
    if (fport == port && faddr == ip_2_ip4 (addr)->addr) {
        udp_recv (pcb, dns_recv_handler, dns);
        return;
    }
}

So mapdsn path is only activated for IPv4-addressed DNS traffic.

Is this the intended behavior? If not I'll be happy to fix it (I am working on a proxy app and in a specific region of the country mobile ISPs only use ipv6 or so it seems).

[heiher]

Hi, mapdns was originally implemented as IPv4-only to keep things simple. I'd be very happy to see a patch adding IPv6 support. Thanks!