.TH BRIDGE 3
.SH NAME
bridge \- Ethernet bridge and IPv4 tunnel
.SH SYNOPSIS
.nf
.B bind -a #B\fIb\fP /net
.sp 0.4v
.B /net/bridge\fIb\fP/ctl
.B /net/bridge\fIb\fP/cache
.B /net/bridge\fIb\fP/log
.B /net/bridge\fIb\fP/stats
.BI /net/bridge\fIb\fP/ n
.BI /net/bridge\fIb\fP/ n /ctl
.BI /net/bridge\fIb\fP/ n /local
.BI /net/bridge\fIb\fP/ n /status
.fi
.SH DESCRIPTION
The
.I bridge
device bridges (copies) packets amongst Ethernet interfaces.
The number
.I b
in the bind is optional and selects a particular bridge
(default 0).
.PP
The
.B /net/bridge0
directory contains
.BR ctl ,
.BR cache ,
.BR log ,
and
.B stats
files, and numbered subdirectories for each physical interface.
.PP
Opening the
.B ctl
file reserves an interface.
The file descriptor returned from the
.IR open (2)
will point to the control file,
.BR ctl ,
of the newly allocated interface.
Reading
.B ctl
returns a text string representing the number of the interface.
Writing
.B ctl
alters aspects of the interface.
The possible
.I ctl
messages are:
.TF cacheflush
.PD
.TP
.BI "bind ether " "name ownhash path"
Treat the device mounted at
.I path
(e.g.,
.LR /net/ether0 )
as an Ethernet medium
and associate it with this bridge (forward its packets to the
other interfaces associated with this bridge).
.I Ownhash
is an `owner hash'.
.TP
.BI "bind tunnel " "name ownhash path path2
Treat the device mounted at
.I path
as a network tunnel (of IPv4 in IPv4),
the device mounted at
.I path2
as an Ethernet medium
and associate them with this bridge
(forward its packets to the
other interfaces associated with this bridge).
Read packets from the
.I path
interface and write them to the
.I path2
interface.
Such tunnels have an MTU of 1400 bytes.
.TP
.BI "unbind " "type address [ownhash]"
Disassociate the interface associated with
.I address
from this bridge.
.I Type
must be
.L ether
or
.LR tunnel .
.TP
.B cacheflush
Clear the cache of (destination MAC address, port) tuples.
.TP
.BI "delay " "delay0 delayn"
Set the
.I delay0
and
.I delayn
parameters.
.I delay0
is the constant microsecond delay per packet
and
.I delayn
is the microsecond delay per byte.
.TP
.BI "set " option
Set bridge
.IR option .
The only known option is
.LR tcpmss ,
which limits the TCP Maximum Segment Size of
TCP packets passing through to 1300 bytes.
.TP
.BI "clear " option
Clear bridge
.IR option .
.PP
Reading
.I stats
returns statistics about the bridge.
.PP
Reading the
.I log
file returns data from the bridge's log
and will block at end of file awaiting new data.
.PP
Reading the
.B cache
file prints the cache of (destination MAC address, port) tuples,
one entry per line.
The format is:
the destination MAC (e.g., Ethernet) address in hex,
port number,
count of packets from this address,
count of packets to this address,
expiry time in seconds since the epoch,
and
.L e
for expired entries or
.L v
for valid entries.
.PP
In a connection subdirectory,
.B ctl
and
.B local
don't do anything,
but
.B status
returns a one-line status summary.
.SH EXAMPLES
Set up a network bridge between two Ethernets
.RL ( #l0
and
.LR #l1 ).
.IP
.EX
bind -a '#B' /net
bind -a '#l1' /net
echo 'bind ether outer 0 /net/ether0' >/net/bridge0/ctl
echo 'bind ether inner 0 /net/ether1' >/net/bridge0/ctl
.EE
.SH "SEE ALSO"
.IR ip (3)
.SH SOURCE
.B /sys/src/9/port/devbridge.c
.SH BUGS
Understands but won't tunnel nor fragment IPv6.