A connection between the subnets behind the gateways <b>moon</b> and <b>sun</b> is set up.
With <b>esp=aes128gcm128-esn-noesn-x25519</b> gateway <b>moon</b> proposes the use of
<b>Extended Sequence Numbers</b> but can also live without them. Gateway <b>sun</b>
defines <b>esp=aes128gcm128-esn-x25519</b> and thus decides on the use of ESN.
The authentication is based on <b>X.509 certificates</b>.
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Upon the successful establishment of the IPsec tunnel, the updown script automatically
inserts iptables-based firewall rules that let pass the tunneled traffic.
In order to test both tunnel and firewall, client <b>alice</b> behind gateway <b>moon</b>
pings client <b>bob</b> located behind gateway <b>sun</b>.
