howto/networksettings.md
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+The first rule of dn42 is always disable `rp_filter`. The second rule of dn42
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+is always disable `rp_filter`. The third rule of dn42 is to allow ip forwarding!
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+No serious, in case some packets are dropped check first if your settings are correct.
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+
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+`rp_filter` also known as reverse path filtering is a security measure,
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+which drop packages, where the reverse route to the source interface
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+does not match the source address of the package. However this often happens in dn42,
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+because routes can be asymmetric (packets can take different routes on the return path).
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+That is why `rp_filter` needs to be disabled:
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+
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+**Note** using sysctl is not persistent. Depending on your linux distribution put it into `/etc/sysctl.conf` or `/etc/sysctl.d`
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+
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+```
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+sysctl -w net.ipv4.conf.all.rp_filter=0 net.ipv4.conf.default.rp_filter=0
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+```
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+
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+Check that its really disabled:
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+```
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+sysctl -a | grep rp_filter
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+```
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+
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+Also the following options must be set.
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+```
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+$ sysctl -w net.ipv4.conf.all.forwarding=1 net.ipv6.conf.all.forwarding=1
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+```
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+
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+Check that ALL your vpn interfaces allow ip forwarding for ipv6/ipv4.
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+```
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+$ sysctl -a | grep forwarding
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+```
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+
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+Happy Routing!
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