BRIDGE(3)                                               BRIDGE(3)

          bridge - Ethernet bridge and IPv4 tunnel

          bind -a #Bb /net

          The bridge device bridges (copies) packets amongst Ethernet
          interfaces.  The number b in the bind is optional and
          selects a particular bridge (default 0).

          The /net/bridge0 directory contains ctl, cache, log, and
          stats files, and numbered subdirectories for each physical

          Opening the ctl file reserves an interface.  The file
          descriptor returned from the open(2) will point to the con-
          trol file, ctl, of the newly allocated interface.  Reading
          ctl returns a text string representing the number of the
          interface.  Writing ctl alters aspects of the interface.
          The possible ctl messages are:

          bind ether name ownhash path
                      Treat the device mounted at path (e.g.,
                      `/net/ether0') as an Ethernet medium and associ-
                      ate it with this bridge (forward its packets to
                      the other interfaces associated with this
                      bridge).  Ownhash is an `owner hash'.

          bind tunnel name ownhash path path2
                      Treat the device mounted at path as a network
                      tunnel (of IPv4 in IPv4), the device mounted at
                      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 path interface and write
                      them to the path2 interface.  Such tunnels have
                      an MTU of 1400 bytes.

          unbind type address [ownhash]
                      Disassociate the interface associated with

     BRIDGE(3)                                               BRIDGE(3)

                      address from this bridge.  Type must be `ether'
                      or `tunnel'.

          cacheflush  Clear the cache of (destination MAC address,
                      port) tuples.

          delay delay0 delayn
                      Set the delay0 and delayn parameters.  delay0 is
                      the constant microsecond delay per packet and
                      delayn is the microsecond delay per byte.

          set option  Set bridge option. The only known option is
                      `tcpmss', which limits the TCP Maximum Segment
                      Size of TCP packets passing through to 1300

          clear option
                      Clear bridge option.

          Reading stats returns statistics about the bridge.

          Reading the log file returns data from the bridge's log and
          will block at end of file awaiting new data.

          Reading the 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
          `e' for expired entries or `v' for valid entries.

          In a connection subdirectory, ctl and local don't do any-
          thing, but status returns a one-line status summary.

          Set up a network bridge between two Ethernets (`#l0' and

               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



          Understands but won't tunnel nor fragment IPv6.