The Ethernet interface, /net/ethern, is a directory containing
subdirectories, one for each distinct Ethernet packet type, and
clone, addr, mtu, ifstats, and stats files. stats and ifstats
are the same as in the subdirectories (see below). Reading addr
returns the MAC address of this interface in hex
with no punctuation and no trailing newline. Reading mtu returns
3 12–byte numbers: the hardware's minimum MTU, the current MTU
and the maximum MTU supported by the interface. The MTU is set
by writing mtu n into the ctl file. The number n (optional in
the bind) is the device number of the card, permitting
multiple cards to be used on a single machine.
Each directory contains files to control the associated connection,
receive and send data, and supply statistics. Incoming Ethernet
packets are demultiplexed by packet type and passed up the corresponding
open connection. Reading from the data file reads packets of that
type arriving from the network. A read will
terminate at packet boundaries. Each write to the data file causes
a packet to be sent. The Ethernet address of the interface is
inserted into the packet header as the source address unless l2bridge
A connection is assigned to a packet type by opening its ctl file
and writing connect n where n is a decimal integer constant identifying
the Ethernet packet type. A type of –1 enables the connection to
receive copies of packets of all types. A type of –2 enables the
connection to receive copies of the first 64 bytes of
packets of all types. If multiple connections are assigned to
a given packet type a copy of each packet is passed up each connection.
Some interfaces also accept unique options when written to the
ctl (or clone) file; see the description of wavelan in plan9.ini(8).
The control messages described in ip(3) under Configuring interfaces
from bridge to headersonly are understood. The additional control
message nonblocking makes
write systems calls to this interface non–blocking iff followed
by nothing or a non–zero integer; a following 0 makes writes block
on a full output queue.
Reading the ctl file returns the decimal index of the associated
connection, 0 through 7. Reading the type file returns the decimal
value of the assigned Ethernet packet type. Reading the stats
file returns status information such as the Ethernet address of
the card and general statistics, independent of the
interface; ifstats contains device–specific data and statistics
about the card. The format of the stats file is stat:value....
In particular, if link is non–zero, mbps is the current speed of
the interface in megabits–per–second. While in and out are the total
number of packets input or output and do differ (in
the case of dropped packets or loop back) from hardware counters.
An interface normally receives only those packets whose destination
address is that of the interface, the broadcast address, ff:ff:ff:ff:ff:ff,
or a a multicast address assigned to the interface. Multicast
addresses are added by writing addmulti ea and remove by writing
remmulti ea to the ctl file.
Multicast addresses are automatically dropped when the connection
is closed. The interface can be made to receive all packets on
the network by writing the string promiscuous to the ctl file.
The interface remains promiscuous until the control file is closed
by all connections requesting promiscuous mode. The
extra packets are passed up connections of types –1 and –2 only.
Writing bridge to the ctl file causes loop back packets to be
ignored. This is useful for layer 3 bridging. Writing l2bridge
also allows the connection to set the source address and receive
packets with any destination address. Writing scanbs [ secs ]
starts a scan for wireless base stations and sets the scanning
interval to secs. Scanning is terminated when the connection is
closed. The default interval is 5s. For wired connections, this
command is ignored.|