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Remove support for ip6tables

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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it has been replaced by nftables.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Closes #44 (no longer applicable).
This commit is contained in:
Tore Anderson
2025-02-02 09:00:39 +01:00
parent 6342488889
commit 6a582bf1e4
3 changed files with 7 additions and 51 deletions
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23
README.pod
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@@ -232,12 +232,6 @@ encountered will be used.
Path to the B<ip> binary from the iproute2 package available at
L<https://www.kernel.org/pub/linux/utils/net/iproute2>. Required.
=item B<cmd-ip6tables=path> (default: assume in $PATH)
Path to the B<ip6tables> binary from the netfilter package available at
L<http://netfilter.org>. Only required for adding ip6tables rules
(see the B<ip6tables-enable> configuration setting).
=item B<cmd-tayga=path> (default: assume in $PATH)
Path to the B<tayga> binary from the TAYGA package available at
@@ -254,22 +248,11 @@ forwarding.
All sysctls that are modified will be restored to their original values when
B<clatd> is shutting down.
=item B<ip6tables-enable=bool> (default: see below)
Controls whether or not B<clatd> should insert ip6tables rules that permit the
forwarding of IPv6 traffic between the CLAT and PLAT devices. Such forwarding
must be permitted for B<clatd> to work correctly. Any rules added will be
removed when B<clatd> is shutting down.
The default is I<yes> if the ip6tables_filter kernel module is loaded, I<no>
if it is not.
=item B<plat-dev> (default: auto-detect)
Which network device is facing the PLAT (NAT64). By default, this is
auto-detected by performing a route table lookup towards the PLAT prefix.
This setting is used when setting up generating the CLAT IPv6 address, and
when setting up ip6tables rules and Proxy-ND entries.
auto-detected by performing a route table lookup towards the PLAT prefix. This
setting is used when generating the CLAT IPv6 address and Proxy-ND entries.
=item B<plat-prefix> (default: auto-detect)
@@ -441,7 +424,7 @@ SOFTWARE.
=head1 SEE ALSO
ip(8), ip6tables(8), tayga(8), tayga.conf(5)
ip(8), tayga(8), tayga.conf(5)
RFC 6052, RFC 6145, RFC 6146, RFC 6877, RFC 7050, RFC 7335 RFC 7755, RFC 7756,
RFC 7757