VEB(4) | Device Drivers Manual | VEB(4)

# NAME

`veb`, `vport` — Virtual Ethernet Bridge network device

# SYNOPSIS

`pseudo-device veb`

# DESCRIPTION

The `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 inet(4) or inet6(4) 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 link0 flag. `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.

pf(4) 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 `vport` 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 traversing `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.

# SEE ALSO

ipsec(4), options(4), pf(4), hostname.if(5), ifconfig(8), netstart(8)

# HISTORY

The `veb` driver first appeared in OpenBSD 6.9.

# AUTHORS

David Gwynne <dlg@openbsd.org>

October 28, 2021 | Debian