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.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.