In some environments the default MTU 1500 is too large. At the same time dhcpd provides a proper MTU to be used in the given env, however dhclient ignores that which result to certain issues. A patch for dhclient-script is available for review here: https://reviews.freebsd.org/D5675
Created attachment 171088 [details] proposed fix, v1
Interface mtu support was committed to FreeBSD's dhclient in r305306. *** This bug has been marked as a duplicate of bug 206721 ***