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52 lines
2 KiB
Markdown
52 lines
2 KiB
Markdown
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# Lws routing
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lws is mainly built around POSIX sockets and operates from the
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information available from those. But in some cases, it needs to go
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a step further and monitor and understand the device routing table.
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## Recognizing loss of routability
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On mobile devices, switching between interfaces and losing / regaining
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connections quickly is a given. But POSIX sockets do not act like
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that, the socket remains connected until something times it out if it
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no longer has a route to its peer, and the tcp timeouts can be in the
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order of minutes.
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In order to do better, lws must monitor and understand how the routing
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table relates to existing connections, dynamically.
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## Linux: netlink
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For linux-based devices you can build in netlink-based route monitoring
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with `-DLWS_WITH_NETLINK=1`, lws aquires a copy of the routing table
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when the context / pt starts up and modifies it according to netlink
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messages from then on.
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On Linux routing table events do not take much care about backing out
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changes made on interface up by, eg, NetworkManager. So lws also
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monitors for link / interface down to remove the related routes.
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## Actions in lws based on routing table
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Both server and client connections now store their peer sockaddr in the
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wsi, and when the routing table changes, all active wsi on a pt are
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checked against the routing table to confirm the peer is still
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routable.
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For example if there is no net route matching the peer and no gateway,
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the connection is invalidated and closed. Similarly, if we are
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removing the highest priority gateway route, all connections to a peer
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without a net route match are invalidated. However connections with
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an unaffected matching net route like 127.0.0.0/8 are left alone.
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## Intergration to other subsystems
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If SMD is built in, on any route change a NETWORK message
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`{"rt":"add|del"}` is issued.
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If SMD is built in, on any route change involving a gateway, a NETWORK
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message `{"trigger":"cpdcheck", "src":"gw-change"}` is issued. If
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Captive Portal Detection is built in, this will cause a new captive
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portal detection sequence.
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