When the NOARP flag is set on the cm interface, it does not employ the address resolution protocol described in arp(4) to dynamically map between Internet and Ethernet addresses on the local network. Instead it uses the least significant 8 bits of the IP address as the hardware address like described in RFC 1051 and RFC 1201.
With the IFF_LINK0 flag cleared IP/ARP/RARP encoding is done according to RFC 1201 that is, with Packet Header Definition Standard header and packet type 212 / 213. The MTU is normally 1500. The IFF_LINK0 flag is cleared by default.
With the IFF_LINK0 flag set, IP and ARP encoding is done according to the deprecated RFC 1051 encoding, that is with simple header, packet type 240 / 241, and the MTU is 507.
When switching between the two modes, use
ifconfig interfacename down up
to switch the MTU.
The following driver specific error messages may be reported: