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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it has been replaced by nftables.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Closes #44 (no longer applicable).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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4
Makefile
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@@ -23,8 +23,8 @@ install:
installdeps:
# .deb/apt-get based distros
if test -x "$(APT_GET)"; then $(APT_GET) -y install perl-base perl-modules libnet-ip-perl libnet-dns-perl libio-socket-ip-perl iproute2 iptables tayga; fi
if test -x "$(APT_GET)"; then $(APT_GET) -y install perl-base perl-modules libnet-ip-perl libnet-dns-perl libio-socket-ip-perl iproute2 tayga; fi
# .rpm/DNF/YUM-based distros
if test -x "$(DNF_OR_YUM)"; then $(DNF_OR_YUM) -y install perl perl-Net-IP perl-Net-DNS perl-IO-Socket-IP perl-File-Temp iproute iptables; fi
if test -x "$(DNF_OR_YUM)"; then $(DNF_OR_YUM) -y install perl perl-Net-IP perl-Net-DNS perl-IO-Socket-IP perl-File-Temp iproute; fi
# If necessary, try to install the TAYGA .rpm using dnf/yum. It is unfortunately not available in all .rpm based distros (in particular CentOS/RHEL).
if test -x "$(DNF_OR_YUM)" && test ! -x "$(TAYGA)"; then $(DNF_OR_YUM) -y install tayga || echo "ERROR: Failed to install TAYGA using dnf/yum, the package is probably not included in your distro. Try enabling the EPEL repo <URL: https://fedoraproject.org/wiki/EPEL> and try again, or install TAYGA <URL: http://www.litech.org/tayga> directly from source."; exit 1; fi