Comment 4 for bug 58927

A bit of additional data about the "interface mtu" request and debian/ubuntu dhcp3 packages:

The setting was disabled during hoary (from changelog):

dhcp3 (3.0.1-1ubuntu4) hoary; urgency=low
  * Revert changes to debian/dhclient.conf, apparently at least some DHCP servers supply broken interface-mtu information, so this isn't safe to enable without broader testing (Ubuntu #8241)

Then the request was enabled in debian and imported to ubuntu:

dhcp3 (3.0.4-6) unstable; urgency=high
  * debian/dhclient.conf: also request the interface-mtu setting (closes: #372689)

The closed bug is a mere wishlist bug, not fixing any actual use case. So I'd suggest the "interface mtu" request is removed because of (very real) potential of still causing breakage.