Makes clatd check if systemd-networkd is aware of any PLAT prefix (which
it may have learned from the PREF64 Router Advertisement option, cf. RFC
8781).
If a prefix is obtained from systemd-network, DNS64-based PLAT prefix
discovery is skipped, as mandated by
https://datatracker.ietf.org/doc/draft-ietf-v6ops-prefer8781/.
However, if the dns64-servers config option is set, clatd will use
DNS64-based PLAT prefix discovery towards the specified servers, and it
will not query systemd-networkd at all.
Closes#32
The first declared target (previously 'install') is use when make is called
without a target argument. This breaks the assumptions of distros.
Further install needs -D to creat the necessary target directories or it
behaves as cp and the target dirs need to exist already.
This works around a bug in Net::DNS (or arguably in IO::Socket::IP)
which causes it to refuse to send queries to IPv4 nameservers (even
localhost), when running on IPv6-only hosts. Since IPv6-only hosts are
the primary use case for clatd, and most modern Linux distributions are
shipping with systemd-resolved listening on 127.0.0.53 by default, this
prevents PLAT prefix discovery from working correctly out of the box.
Forcing Net::DNS to use an IPv6 socket, by simply substituting all IPv4
addresses in the name server as IPv4-mapped IPv6 addreses, successfully
works around this problem.
This bug has been present in Net::DNS since version 1.03 (more
specifically since SVN r1406, dated 2015-10-05). This version started
defaulting to using IO::Socket::IP for all sockets, so it is no longer
necessary to require it explicitly in clatd.
For more info:
https://rt.cpan.org/Public/Bug/Display.html?id=158714 (Net::DNS)
https://rt.cpan.org/Public/Bug/Display.html?id=132760 (IO::Socket::IP)
UFW is the standard local firewall framework in Debian-based
distributions. If it is installed and active, add rules that permit
routed traffic between the CLAT and the PLAT prefix. This traffic is
dropped by the default UFW ruleset, leading to issues such as #42.
This moves the route for IPv6 traffic from the PLAT to the CLAT into a
separate routing table, and uses the Linux kernel's routing policy
framework to redirect traffic into this routing table.
This makes it possible to set `clat-v6-addr` to an address also used by
the main host OS, removing the requirement for having a dedicated
secondary address assigned to the CLAT.
Additionally, support using nftables to set a connection tracking mark
on outbound connections from the CLAT, and ensuring only return traffic
matching that mark is returned back to the CLAT. This makes it possible
for the CLAT to share an IPv6 address with the main host OS without
breaking connectivity to DNS64-synthesised IPv6 addresses.
The trade-off of using a connection tracking mark is that the CLAT can
not receive unsolicited traffic from the IPv4 Internet via the PLAT.
However in the common case, where the PLAT is Stateful NAT64, that is
the case no matter what.
Closes#25.
The ip6tables frameworks has been deprecated for quite a while now, as
it has been replaced by nftables. On modern distributions, rules added
with ip6tables are just converted to nftables rules and are added to an
ip6tables compatibility table there. This changed the name of the kernel
modules, breaking ip6tables auto-detection (cf. issues #42 and #44).
Unfortunately, due to the way nftables works, these rules can no longer
be relied upon to ensure the CLAT traffic is allowed. This is due to the
fact that in nftables, *all* chains that hook into a packet's path must
return an «accept» verdict in order for the packet to be ultimately
accepted, while it is enough for a single chain to return a «drop»
verdict in order for the packet to be dropped.
That means that the rules that accepts CLAT traffic might be overridden
by a «default drop» rule added to another chain in another table, e.g.,
by firewalld or similar local firewall frameworks. See #23 for an
example of this.
On the other hand, if there is no drop rule anywhere, the rules added by
clatd are superfluous to begin with, as the default kernel behaviour is
to accept the packages.
Therefore just remove support for ip6tables entirely. Users of
firewalld, ufw, or similar local firewall frameworks will need to make
sure that rules are added in those frameworks that permit the CLAT
traffic, e.g., by using `script-up`, like so for ufw:
```
script-up=ufw route allow in on $clat_dev out on $plat_dev
```
Native support for adding rules to the most common local firewall
frameworks might be added in the future.
Closes#44 (no longer applicable).
Perl module IO::Socket::INET6 is obsolete and recomended one is
IO::Socket::IP, which has compatibility to old one.
btw: Net::DNS was rewrited to use IO::Socket::IP.
Don't assume that utilities such as systemctl or initctl is found in a certain
specific path. Instead look for them in $PATH. This applies to both the
Makefile and the NetworkManager dispatcher script.
Resolves#11.
