  <varlistentry>
  <term><emphasis remap='B'>esn</emphasis></term>
  <listitem>
<para>Whether or not to enable Extended Sequence Number (ESN) for the IPsec SA. This
option is only implemented for IKEv2. ESN is typically used for very high-speed links (10Gbps or faster) where the
standard 32 bit sequence number is exhausted too quickly, causing IPsec SA's
rekeys to happen too often. Accepted values are
<emphasis remap='B'>either</emphasis> (the default),
<emphasis remap='B'>yes</emphasis> and <emphasis remap='B'>no</emphasis>.
If <emphasis remap='I'>either</emphasis> is specified as an initiator, the responder will make the choice. As
a responder, if <emphasis remap='I'>either</emphasis> is received, <emphasis remap='I'>yes</emphasis> is picked.
</para>
<para>If replay-window is set to 0, ESN is disabled as some (most?) IPsec stacks won't support ESN in such
a configuration.
</para>
  </listitem>
  </varlistentry>

