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networkd: stop managing per-interface IP forwarding settings

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As it turns out the kernel does not support per-interface IPv6 packet
forwarding controls (unlike as it does for IPv4), but only supports a
global option (#1597). Also, the current per-interface management of the
setting isn't really useful, as you want it to propagate to at least one
more interface than the one you configure it on. This created much grief
(#1411, #1808).

Hence, let's roll this logic back and simplify this again, so that we
can expose the same behaviour on IPv4 and IPv6 and things start to work
automatically again for most folks: if a network with this setting set
is set up we propagate the setting into the global setting, but this is
strictly one-way: we never reset it again, and we do nothing for network
interfaces where this setting is not enabled.

Fixes: #1808, #1597.
This commit is contained in:
Lennart Poettering
2015-11-13 13:02:50 +01:00
parent d68e2e59b3
commit 765afd5c4d
3 changed files with 57 additions and 42 deletions
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man/systemd.network.xml
+18 -19
View File
@@ -363,29 +363,28 @@
</varlistentry>
<varlistentry>
<term><varname>IPForward=</varname></term>
<listitem><para>Configures IP forwarding for the network
interface. If enabled, incoming packets on the network
interface will be forwarded to other interfaces according to
the routing table. Takes either a boolean argument, or the
values <literal>ipv4</literal> or <literal>ipv6</literal>,
which only enables IP forwarding for the specified address
family, or <literal>kernel</literal>, which preserves existing sysctl settings.
This controls the
<filename>net.ipv4.conf.&lt;interface&gt;.forwarding</filename>
and
<filename>net.ipv6.conf.&lt;interface&gt;.forwarding</filename>
sysctl options of the network interface (see <ulink
<listitem><para>Configures IP packet forwarding for the
system. If enabled, incoming packets on any network
interface will be forwarded to any other interfaces
according to the routing table. Takes either a boolean
argument, or the values <literal>ipv4</literal> or
<literal>ipv6</literal>, which only enable IP packet
forwarding for the specified address family. This controls
the <filename>net.ipv4.ip_forward</filename> and
<filename>net.ipv6.conf.all.forwarding</filename> sysctl
options of the network interface (see <ulink
url="https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt">ip-sysctl.txt</ulink>
for details about sysctl options). Defaults to
<literal>no</literal>.</para>
<para>Note: unless this option is turned on, or set to <literal>kernel</literal>,
no IP forwarding is done on this interface, even if this is
globally turned on in the kernel, with the
<filename>net.ipv4.ip_forward</filename>,
<filename>net.ipv4.conf.all.forwarding</filename>, and
<filename>net.ipv6.conf.all.forwarding</filename> sysctl
options.</para>
<para>Note: this setting controls a global kernel option,
and does so one way only: if a network that has this setting
enabled is set up the global setting is turned on. However,
it is never turned off again, even after all networks with
this setting enabled are shut down again.</para>
<para>To allow IP packet forwarding only between specific
network interfaces use a firewall.</para>
</listitem>
</varlistentry>
<varlistentry>