BAH(4)               NetBSD/amiga Kernel Interfaces Manual              BAH(4)

NAME
     bah -- ARCnet network driver for SMC COM90C26 based boards

SYNOPSIS
     bah* at zbus0

DESCRIPTION
     The bah interface provides access to the 2.5 Mb/s ARCnet network via the
     SMC COM90C26 + COM90C32 ARCnet chip set.

     Each of the host's network addresses is specified at boot time with an
     SIOCSIFADDR ioctl(2).  The interface MTU is 507 for protocols that do not
     use link level fragmentation and 60480 bytes for the others. The routing
     layer may specify additional limits.
     Currently supported protocols are IPv4(+ARP), and IPv6.

IP VERSION 4 CONSIDERATIONS
     When the NOARP flag is set on the bah 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 hardware address,
     as described in RFC 1051 and  RFC 1201.

     With the IFF_LINK0 flag cleared, IP and ARP encoding is done according to
     the deprecated, but popular among Amiga users, RFC 1051 encoding (that
     is, with simple header, packet type 240 / 241), and the MTU is 507.

     With the IFF_LINK0 flag set, 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.

     When switching between the two modes, do a ifconfig interfacename down up
     to switch the MTU.

     When the IFF_LINK2 flag is set, ARP packets are sent with the protocol
     type encoded as it would be in the  ARCnet header, and decoded to the
     right protocol encoding on reception. According to "assigned numbers",
     this is wrong, but some legacy software (namely, AmiTCP 3.0beta) shows
     this bug.

HARDWARE
     The bah interface supports the following Zorro II expansion cards:

           A2060      Commodore's ARCnet card, manufacturer 514, product 9

           AMERISTAR  Ameristar's ARCnet card, manufacturer 1053, product 9

SEE ALSO
     arp(4), inet(4), intro(4), ifconfig(8)

     P.A. Prindeville, "Standard for the transmission of IP datagrams and ARP
     packets over ARCNET networks.", RFC, 1051, March 1988.

     D. Provan, "Transmitting IP traffic over ARCNET networks.", RFC, 1201,
     February 1991.

     I. Souvatzis, "Transmission of IPv6 Packets over ARCnet Networks.", RFC,
     2497, January 1999.

     ARCnet Packet Header Definition Standard, Novell Inc., 1989

STANDARDS
     RFC 1051/RFC1201 with ARP, or without, using direct mapping of lower 8 IP
     address bits instead.

HISTORY
     The Amiga bah interface first appeared in NetBSD 1.1.  ARP support was
     added in NetBSD 1.3.

AUTHORS
     Ignatios Souvatzis

NetBSD 5.0_STABLE                May 31, 1995                NetBSD 5.0_STABLE
