1.\" 2.\" $FreeBSD$ 3.\" 4.Dd September 28, 1998 5.Dt BRIDGE 4 6.Os 7.Sh NAME 8.Nm bridge 9.Nd bridging support 10.Sh DESCRIPTION 11Starting from version 2.2.8, 12.Fx 13supports bridging on ethernet-type 14interfaces. 15This is achieved using the following option 16.Bd -literal 17 options BRIDGE 18.Ed 19.Pp 20in the kernel config file, and is controlled by two 21.Nm sysctl 22variables: 23.Bd -literal 24 net.link.ether.bridge 25.Ed 26.Pp 27Set to 1 to enable bridging, set to 0 to disable it 28.Bd -literal 29 net.link.ether.bridge_ipfw 30.Ed 31.Pp 32Set to 1 to enable 33.Nm ipfw 34filtering on bridged packets. 35Note that 36.Nm ipfw 37rules only apply 38to IP packets. 39Non-IP packets are subject to the default 40.Nm ipfw 41rule 42.Pq number 65535 43which must be an 44.Ar allow 45rule if we want ARP and other non-IP packets to flow through the 46bridge. 47.Sh BUGS 48.Pp 49Care must be taken not to construct loops in the bridge topology. 50The kernel supports only a primitive form of loop detection, by disabling 51some interfaces when a loop is detected. 52No support for a daemon running the 53spanning tree algorithm is currently provided. 54.Pp 55With bridging active, interfaces are in promiscuous mode, 56thus causing some load on the system to receive and filter 57out undesired traffic. 58.Pp 59Extended functionality to enable bridging selectively on clusters 60of interfaces is still in the works. 61.Pp 62Interfaces that cannot be put into promiscuous mode or that don't 63support sending packets with arbitrary Ethernet source addresses 64are not compatible with bridging. 65.Sh SEE ALSO 66.Xr ip 4 , 67.Xr ng_bridge 4 , 68.Xr ipfw 8 , 69.Xr sysctl 8 70.Sh HISTORY 71.Nm 72bridging was introduced in 73.Fx 2.2.8 74by 75.An Luigi Rizzo Aq luigi@iet.unipi.it . 76