Guidelines for Firewall Mode

You can create up to 250 bridge groups, with 64 interfaces per bridge group.

Each directly-connected network must be on the same subnet.

The threat defense device does not support traffic on secondary networks; only traffic on the same network as the BVI IP address is supported.

An IP address for the BVI is required for each bridge group for to-the-device and from-the-device management traffic, as well as for data traffic to pass through the threat defense device. For IPv4 traffic, specify an IPv4 address. For IPv6 traffic, specify an IPv6 address.

You can only configure IPv6 addresses manually.

The BVI IP address must be on the same subnet as the connected network. You cannot set the subnet to a host subnet (255.255.255.255).

Management interfaces are not supported as bridge group members.

For multi-instance mode, shared interfaces are not supported for bridge group member interfaces (in transparent mode or routed mode).

For the threat defense virtual on VMware with bridged ixgbevf interfaces, transparent mode is not supported, and bridge groups are not supported in routed mode.

For the Firepower 1010, you cannot mix logical VLAN interfaces and physical firewall interfaces in the same bridge group.

For the Firepower 4100/9300, data-sharing interfaces are not supported as bridge group members.

In transparent mode, you must use at least 1 bridge group; data interfaces must belong to a bridge group.

In transparent mode, do not specify the BVI IP address as the default gateway for connected devices; devices need to specify the router on the other side of the threat defense as the default gateway.

In transparent mode, the default route, which is required to provide a return path for management traffic, is only applied to management traffic from one bridge group network. This is because the default route specifies an interface in the bridge group as well as the router IP address on the bridge group network, and you can only define one default route. If you have management traffic from more than one bridge group network, you need to specify a regular static route that identifies the network from which you expect management traffic.

Transparent mode is not supported on threat defense virtual instances deployed on Amazon Web Services, Microsoft Azure, Google Cloud Platform, and Oracle Cloud Infrastructure.

In routed mode, to route between bridge groups and other routed interfaces, you must name the BVI.

In routed mode, threat defense-defined EtherChannel interfaces are not supported as bridge group members. EtherChannels on the Firepower 4100/9300 can be bridge group members.

Bidirectional Forwarding Detection (BFD) echo packets are not allowed through the threat defense when using bridge group members. If there are two neighbors on either side of the threat defense running BFD, then the threat defense will drop BFD echo packets because they have the same source and destination IP address and appear to be part of a LAND attack.