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TPMR(4) Device Drivers Manual TPMR(4)

tpmrIEEE 802.1Q Two-Port MAC Relay interface

pseudo-device tpmr

The 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 using the ifconfig tpmrN create command or by setting up a hostname.if(5) configuration file for netstart(8).

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 and bridge(4):

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 used:

# 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 bridge(4) as it filters those protocols.

If Host A connected to Router B has the external IP address on em0, Host D connected to Router C has the external IP address 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 ----+

Create the tpmr and etherip(4) interfaces:

# ifconfig etherip0 create
# ifconfig tpmr0 create link0

Configure the etherip interface:

(on Host A) # ifconfig etherip0 tunnel up
(on Host D) # ifconfig etherip0 tunnel 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)

The tpmr driver first appeared in OpenBSD 6.6.

July 28, 2021 OpenBSD-current