Good catch, I've filed a problem report 2848646. Vincent On Friday, January 25, 2002, at 03:12 PM, Andrew Gallatin wrote: Vincent Lubet writes: On Friday, January 25, 2002, at 02:26 PM, Andrew Gallatin wrote: While I've got your attention: Do you have any plans to accommodate jumbo frames? It looks like I'm going to have to somehow override ether_inet_prmod_ioctl() to allow setting a 9000 byte mtu on my device. For now, I'm just resetting if_mtu after calling ether_ifattach(), but it would be nice to allow the user to change the mtu.. This should work as the loopback interface has a MTU of 16 KB -- the MTU is device specific. No, for an ethernet interface, mtu ioctls are caught by ether_inet_prmod_ioctl(), which does this (excuse the whitespace mangling my my mailer): case SIOCSIFMTU: /* * Set the interface MTU. */ if (ifr->ifr_mtu > ETHERMTU) { error = EINVAL; } else { ifp->if_mtu = ifr->ifr_mtu; } break; The loopback interface is not an ethernet interface, so it can have a larger mtu.. Drew