NAME
pair —
virtual Ethernet interface
pair
SYNOPSIS
pseudo-device pair
DESCRIPTION
The pair interface simulates a normal
Ethernet interface by encapsulating standard network frames with an Ethernet
header, specifically for use in a pair of interfaces that are interconnected
with each other.
To use it, the administrator needs to create two
pair interfaces and connect them; the interfaces are
‘patched’, as would be done with physical network ports. All
packets that are sent on the first interface are received on the second
interface.
EXAMPLES
Set up a pair of interfaces where each of them is a member of a different rdomain(4):
# ifconfig pair1 rdomain 1 10.1.1.1/24 up # ifconfig pair2 rdomain 2 10.1.1.2/24 up # ifconfig pair1 patch pair2 # route -T 1 exec ping 10.1.1.2
When adding multiple pair to multiple
bridge(4) interfaces, it is possible to create a loop; the system
load will go up while it is busy sending packets from one bridge to another
and back. By design, the driver does not prevent such loops by itself, but
it is possible to use the Spanning Tree Protocol (STP) to detect and remove
loops in the virtual network topology:
# ifconfig pair0 up # ifconfig pair1 rdomain 1 patch pair0 up # ifconfig pair2 up # ifconfig pair3 rdomain 1 patch pair2 up # ifconfig bridge0 add pair0 add pair2 stp pair0 stp pair2 up # ifconfig bridge1 add pair1 add pair3 stp pair1 stp pair3 up
SEE ALSO
bridge(4), inet(4), inet6(4), rdomain(4), vether(4), hostname.if(5), ifconfig(8), netstart(8)
HISTORY
The pair interface first appeared in
OpenBSD 5.9.
AUTHORS
The pair driver is based on
vether(4) by Theo de Raadt
<deraadt@openbsd.org>.
It has been extended and turned into pair by
Reyk Floeter
<reyk@openbsd.org>.
CAVEATS
Unlike
vether(4), the pair interface cannot be used
as a stand-alone member in a
bridge(4): the link state remains down until it is connected to the
second interface. Any associated routes will be marked down until it is
patched. Use vether(4) as a bridge endpoint for routing purposes
instead.
BUGS
Like tun(4), the Ethernet address chosen will be partially random, and may occasionally collide with another address.