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
amiga/intro(4), arp(4), inet(4), ifconfig(8) RFC, 1051, March 1988, Standard for the transmission of IP datagrams and ARP packets over ARCNET networks., P.A. Prindeville. RFC, 1201, Transmitting IP traffic over ARCNET networks., D. Provan, February 1991. RFC, 2497, Transmission of IPv6 Packets over ARCnet Networks., I. Souvatzis, 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