55 lines
2.9 KiB
ReStructuredText
55 lines
2.9 KiB
ReStructuredText
WAN support
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===========
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As the WAN port of a node will be connected to a user's private network, it
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is essential that the node only uses the WAN when it is absolutely necessary.
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There are two cases in which the WAN port is used:
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* Mesh VPN (package ``gluon-mesh-vpn-fastd``)
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* 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
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the mesh's DNS servers and use these for all other name resolution.
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If the device does not feature a WAN port, the LAN port is configured as WAN port.
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In case such a device has multiple LAN ports, all these can be used as WAN.
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Devices, which feature a "hybrid" port (labelled as WAN/LAN), this port is used as WAN.
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This behavior can be reversed using the ``single_as_lan`` site.conf option.
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Routing tables
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~~~~~~~~~~~~~~
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As a node may get IPv6 default routes both over the WAN and the mesh, Gluon
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uses two routing tables for IPv6. As all normal traffic should go over the mesh,
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the mesh routes are added to the default table (table 0). All routes on the WAN interface
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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
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bit 1 set though table 1.
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libpacketmark
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~~~~~~~~~~~~~
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*libpacketmark* is a library which can be loaded with ``LD_PRELOAD`` and will set the packet mark of all
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sockets created by a process in accordance with the ``LIBPACKETMARK_MARK`` environment variable. This allows setting
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the packet mark for processes which don't support this themselves. The process must run as root (or at least
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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
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run after the packet has been created, to even when the packet mark is changed and the packet is re-routed, the
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source address won't be rewritten to the default source address of the newly chosen route. *libpacketmark* avoids
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this issue as the packet mark will already be set when the packet is created.
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gluon-wan-dnsmasq
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~~~~~~~~~~~~~~~~~
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To separate the DNS servers in the mesh from the ones on the WAN, the ``gluon-wan-dnsmasq`` package provides
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a secondary DNS daemon which runs on ``127.0.0.1:54``. It will automatically use all DNS servers explicitly
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configured in ``/etc/config/gluon-wan-dnsmasq`` or received via DNS/RA on the WAN port. It is important that
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no DNS servers for the WAN interface are configured in ``/etc/config/network`` and that ``peerdns`` is set to 0
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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
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with the primary group ``gluon-mesh-vpn`` to ``127.0.0.1:54``, thus making fastd use the secondary DNS daemon.
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