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docs: add documentation for the WAN configuration
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WAN support | ||
=========== | ||
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As the WAN port of a node will be connected to a user's private network, it | ||
is essential that the node only uses the WAN when it is absolutely necessary. | ||
There are two cases in which the WAN port is used: | ||
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* Mesh VPN (package ``gluon-mesh-vpn-fastd`` | ||
* DNS to resolve the VPN servers' addresses (package ``gluon-wan-dnsmasq``) | ||
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After the VPN connection has been established, the node should be able to reach | ||
the mesh's DNS servers and use these for all other name resolution. | ||
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Routing tables | ||
~~~~~~~~~~~~~~ | ||
As a node may get IPv6 default routes both over the WAN and the mesh, Gluon | ||
uses two routing tables for IPv6. As all normal traffic should go over the mesh, | ||
the mesh routes are added to the default table (table 0). All routes on the WAN interface | ||
are put into table 1 (see ``/lib/gluon/upgrade/110-network`` in ``gluon-core``). | ||
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There is also an *ip -6 rule* which routes all IPv6 traffic with a packet mark with the | ||
bit 1 set though table 1. | ||
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libpacketmark | ||
~~~~~~~~~~~~~ | ||
*libpacketmark* is a library which can be loaded with ``LD_PRELOAD`` and will set the packet mark of all | ||
sockets created by a process in accordance with the ``LIBPACKETMARK_MARK`` environment variable. This allows setting | ||
the packet mark for processes which don't support this themselves. The process must run as root (or at least | ||
with ``CAP_NET_ADMIN``) for this to work. | ||
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Unfortunately there's no nice way to set the packet mark via iptables for outgoing packets. The iptables will | ||
run after the packet has been created, to even when the packet mark is changed and the packet is re-routed, the | ||
source address won't be rewritten to the default source address of the newly chosen route. *libpacketmark* avoids | ||
this issue as the packet mark will already be set when the packet is created. | ||
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gluon-wan-dnsmasq | ||
~~~~~~~~~~~~~~~~~ | ||
To separate the DNS servers in the mesh from the ones on the WAN, the ``gluon-wan-dnsmasq`` package provides | ||
a secondary DNS daemon which runs on ``127.0.0.1:54``. It will automatically use all DNS servers explicitly | ||
configured in ``/etc/config/gluon-wan-dnsmasq`` or received via DNS/RA on the WAN port. It is important that | ||
no DNS servers for the WAN interface are configured in ``/etc/config/network`` and that ``peerdns`` is set to 0 | ||
so the WAN DNS servers aren't leaked to the primary DNS daemon. | ||
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*libpacketmark* is used to make the secondary DNS daemon send its requests over the WAN interface. | ||
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The package ``gluon-mesh-vpn-fastd`` provides an iptables rule which will redirect all DNS requests from processes running | ||
with the primary group ``gluon-fastd`` to ``127.0.0.1:54``, thus making fastd use the secondary DNS daemon. |
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