IEEE 802.1Q Two-Port MAC Relay
tpmr driver implements an 802.1Q
(originally 802.1aj) Two-Port MAC Relay (TPMR). A TPMR is a simplified
Ethernet bridge with exactly two member ports, and it unconditionally relays
Ethernet packets between those ports.
tpmr interfaces can be created at runtime
create command or by setting up a
hostname.if(5) configuration file for
Other forms of Ethernet bridging are available using the bridge(4) Ethernet bridge driver and the veb(4) Virtual Ethernet Bridge device. Link aggregation of Ethernet interfaces can be achieved using the aggr(4) and trunk(4) drivers.
The following ioctl(2) calls and their structures are commonly use by
tpmr can be used to cross-connect Ethernet
devices that support different physical media. For example, a device that
supports a 100baseTX half-duplex connection can be connected to a switch
with 1000baseSX optical ports by using
tpmr with a
pair of physical network interfaces, each of which supports the required
media types. If fxp(4) is used to connect to the 100baseTX device, and
em(4) is used to
connect to the 1000baseSX switch, the following configuration can be
# ifconfig tpmr0 create # ifconfig tpmr0 add fxp0 add em0 # ifconfig fxp0 up # ifconfig em0 up # ifconfig tpmr0 up
Multiple TPMRs can be chained to transport Ethernet traffic for a
pair of devices over another network. Given two physically separate Ethernet
switches, TPMRs can be used as follows to provide a point-to-point Ethernet
link between them.
tpmr with the
link0 flag set allows the use of the Link
Aggregation Control Protocol (LACP) or Spanning Tree Protocol (STP) by the
switches to detect communication failures or connectivity loops
respectively, which is not possible using
as it filters those protocols.
If Host A connected to Router B has the external IP address 192.0.2.10 on em0, Host D connected to Router C has the external IP address 198.51.100.14 on em0, and both hosts have em1 connected to the switches, the following configuration can be used to connect the switches together. etherip(4) is used to transport the Ethernet packets over the IP network.
Switch X ---- Host A ---------- tunnel ----------- Host D ---- Switch E \ / \ / +---- Router B ---- Router C ----+
# ifconfig etherip0 create # ifconfig tpmr0 create link0
Configure the etherip interface:
(on Host A) # ifconfig etherip0 tunnel 192.0.2.10 198.51.100.14 up (on Host D) # ifconfig etherip0 tunnel 198.51.100.14 192.0.2.10 up
Add the etherip interface and physical interface to the TPMR:
# ifconfig tpmr0 add em1 add etherip0 up
An equivalent setup using MPLS pseudowires instead of IP as the transport can be built using mpw(4) interfaces.
aggr(4), bridge(4), pf(4), trunk(4), veb(4), hostname.if(5), ifconfig(8), netstart(8)
tpmr driver first appeared in