— Virtual Ethernet Bridge
veb pseudo-device supports the
creation of a single layer 2 Ethernet network between multiple ports.
Ethernet interfaces are added to the
veb bridge to
be used as ports. Unlike bridge(4),
veb takes over the
operation of the interfaces that are added as ports. They are then
independent of the host network stack: the individual Ethernet ports no
longer function as independent devices and cannot be configured with
addresses or other layer-3 features themselves.
The Ethernet network managed by
veb can be
connected to the network stack as a whole by creating a
vport interface and attaching it as a port to the
bridge. From the perspective of the host network stack, a
vport interface acts as a normal interface connected
to an Ethernet network and can be configured with addresses.
veb is a learning bridge that maintains a
table of Ethernet addresses and the port that each address is reachable
with. The bridge learns about the reachability of Ethernet addresses by
reading the source address on packets received by ports, and then entering
the address and port into the table dynamically. Static address entries may
also be configured in the table, disabling dynamic learning for that
address. Ethernet address learning can be disabled on individual ports.
When forwarding a packet, the address table is searched for the destination Ethernet address and the packet is sent to the associated port in the table entry. If no entry is found in the table, or the packet is addressed to a multicast or broadcast address, the packet is flooded to all other ports on the bridge. Flooding of packets to unknown unicast addresses can be disabled on individual ports.
veb provides multiple mechanisms for
filtering packets traversing the bridge. By default it filters IEEE 802.1Q
VLAN and SVLAN packets, but can be configured to forward them by setting the
veb can filter Ethernet packets entering
or leaving ports using bridge rules. Ports can be configured as members of
protected domains to restrict communication between them.
can be used to filter IP packets as they enter or leave the bridge. By
default this filtering is disabled, but can be enabled by setting the link1
flag. The exception to this policy is on
interfaces, where pf(4) runs as packets enter and leave the network stack regardless of
the value of the link1 flag. A consequence of this behaviour is that packets
vport interfaces appear to travel in the
opposite direction to packets travelling over other ports.
veb supports the addition of span ports to
the bridge. Span ports transmit a copy of every packet received by the
bridge, allowing for passive monitoring of traffic on a separate host.
ipsec(4), options(4), pf(4), hostname.if(5), ifconfig(8), netstart(8)
veb driver first appeared in
David Gwynne <email@example.com>