strongSwan

h1. NAT Traversal

h2. IKEv1

Before [[5.0.0]], NAT discovery and traversal had to be enabled by setting _nat_traversal=yes_ in the [[ConfigSetupSection|config setup]] section of [[IpsecConf|ipsec.conf]]. Otherwise strongSwan 4.x's IKEv1 pluto daemon would not accept incoming IKE packets with a UDP source port different from 500. Since [[5.0.0]] IKEv1 traffic is handled by the charon daemon which supports NAT traversal according to "RFC 3947":http://tools.ietf.org/html/rfc3947 without enabling it explicitly.

h2. IKEv2

The IKEv2 protocol includes NAT traversal in the core standard, but it's optional to implement. strongSwan implements it, and there is no configuration involved. The @NAT_DETECTION_SOURCE/DESTINATION_IP@ notifications included in the @IKE_SA_INIT@ exchange indicate the peers NAT-T capability and if a NAT situation is detected, UDP encapsulation is activated for IPsec.

strongSwan starts sending keep-alive packets if it is behind a NAT router to keep the mappings on the NAT device intact.

NAT traversal cannot be disabled in the charon daemon. If you don't like automatic port floating to UDP/4500 due to the MOBIKE protocol (RFC 4555) which happens even if no NAT situation exists then you can disable MOBIKE by adding

<pre>

mobike=no

</pre>

to ipsec.conf in the connection definition.