illumos gate

RFC 2132 describes a DHCP option for setting the Interface MTU to something other than the default of 1500:

5.1. Interface MTU Option

   This option specifies the MTU to use on this interface.  The MTU is
   specified as a 16-bit unsigned integer.  The minimum legal value for
   the MTU is 68.

   The code for this option is 26, and its length is 2.

    Code   Len      MTU
   +-----+-----+-----+-----+
   |  26 |  2  |  m1 |  m2 |
   +-----+-----+-----+-----+

We should provide support for using this option. In particular, the Google Compute Engine (GCE) hypervisor environment requires the guest to use an MTU of 1460 bytes, and will tell the guest to do this via DHCP.