1.\" $OpenBSD: bridge.4,v 1.75 2016/09/04 18:55:08 jmc Exp $ 2.\" 3.\" Copyright (c) 1999-2001 Jason L. Wright (jason@thought.net) 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 17.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 18.\" DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, 19.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 23.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 24.\" ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25.\" POSSIBILITY OF SUCH DAMAGE. 26.\" 27.Dd $Mdocdate: September 4 2016 $ 28.Dt BRIDGE 4 29.Os 30.Sh NAME 31.Nm bridge 32.Nd Ethernet bridge interface 33.Sh SYNOPSIS 34.Cd "pseudo-device bridge" 35.Pp 36.In sys/types.h 37.In net/if.h 38.In netinet/in.h 39.In netinet/if_ether.h 40.In net/if_bridge.h 41.Sh DESCRIPTION 42The 43.Nm 44device creates a logical link between two or more Ethernet interfaces or 45encapsulation interfaces (see 46.Xr etherip 4 ) . 47This link between the interfaces selectively forwards frames from 48each interface on the bridge to every other interface on the bridge. 49A bridge can serve several services, including isolation of traffic between 50sets of machines so that traffic local to one set of machines is not 51available on the wire of another set of machines, and it can act as 52a transparent filter for 53.Xr ip 4 54datagrams. 55.Pp 56A 57.Nm 58interface can be created at runtime using the 59.Ic ifconfig bridge Ns Ar N Ic create 60command or by setting up a 61.Xr hostname.if 5 62configuration file for 63.Xr netstart 8 . 64.Pp 65The bridges provided by this interface are learning bridges with 66filtering; see 67.Xr pf 4 . 68In general a bridge works like a hub, forwarding traffic from one interface 69to another. 70It differs from a hub in that it will "learn" which machines 71are on each of its attached segments by actively listening to 72incoming traffic and examining the headers of each frame. 73A table is built containing the MAC address and segment to which the 74MAC address is attached. 75This allows a bridge to be more selective about what it forwards, 76which can be used to reduce traffic on a set of segments and also to provide 77an IP firewall without changing the topology of the network. 78.Pp 79The algorithm works as follows by default, but can be modified via 80.Xr ioctl 2 81or the utility 82.Xr ifconfig 8 . 83When a frame comes in, the origin segment and the source address are 84recorded. 85If the bridge has no knowledge about where the destination is to be found, 86the bridge will forward the frame to all attached segments. 87If the destination is known to be on a different segment from its origin, the 88bridge will forward the packet only to the destination segment. 89If the destination is on the same segment as the origin segment, the bridge 90will drop the packet because the receiver has already had a chance to see 91the frame. 92Before forwarding a frame, the bridge will check to see if the packet 93contains an 94.Xr ip 4 95or 96.Xr ip6 4 97datagram; if so, the datagram is run through the 98pf interface so that it can be filtered. 99See the 100.Sx NOTES 101section for details. 102.Sh SPANNING TREE 103The bridge has support for 802.1D-2004 Spanning Tree Protocol (STP), 104which can be used to detect and remove loops in a network topology. 105Using the 106.Cm stp 107or 108.Cm -stp 109commands 110to 111.Nm , 112STP can be enabled or disabled on each port. 113.Pp 114The bridge will use the Rapid Spanning Tree Protocol (RSTP) by default 115to allow rapid transitions to the forwarding state. 116The 117.Cm proto 118command to 119.Nm 120can be used to force operation in the common Spanning Tree Protocol 121without rapid state transitions. 122Note that RSTP will be compatible with remote bridges running common STP. 123.Pp 124STP will not work on 125.Xr etherip 4 126members because they lack a hardware MAC address. 127.Sh SPAN PORTS 128The bridge can have interfaces added to it as span ports. 129Span ports transmit a copy of every frame received by the bridge. 130This is most useful for snooping a bridged network passively on 131another host connected to one of the span ports of the bridge. 132Span ports cannot be bridge members; instead, the 133.Cm addspan 134and 135.Cm delspan 136commands are used to add and delete span ports to and from a bridge. 137.Sh IOCTLS 138A 139.Nm 140interface responds to all of the 141.Xr ioctl 2 142calls specific to other interfaces listed in 143.Xr netintro 4 . 144The following 145.Xr ioctl 2 146calls are specific to 147.Nm 148devices. 149They are defined in 150.In sys/sockio.h . 151Some 152.Xr ioctl 2 153calls are used by 154.Xr switch 4 155as well. 156.Bl -tag -width Ds 157.It Dv SIOCBRDGIFS Fa "struct ifbifconf *" 158Retrieve member interface list from a bridge. 159This request takes an 160.Vt ifbifconf 161structure (see below) as a value-result parameter. 162The 163.Va ifbic_len 164field should be initially set to the size of the buffer 165pointed to by 166.Va ifbic_buf . 167On return it will contain the length, in bytes, of the configuration 168list. 169.Pp 170Alternatively, if the 171.Va ifbic_len 172passed in is set to 0, 173.Dv SIOCBRDGIFS 174will set 175.Va ifbic_len 176to the size that 177.Va ifbic_buf 178needs to be to fit the entire configuration list, 179and will not fill in the other parameters. 180This is useful for determining the exact size that 181.Va ifbic_buf 182needs to be in advance. 183.Pp 184The argument structure is defined as follows: 185.Bd -literal 186struct ifbreq { 187 char ifbr_name[IFNAMSIZ]; /* bridge ifs name */ 188 char ifbr_ifsname[IFNAMSIZ];/* member ifs name */ 189 u_int32_t ifbr_ifsflags; /* member ifs flags */ 190 u_int8_t ifbr_state; /* member stp state */ 191 u_int8_t ifbr_priority; /* member stp priority */ 192 u_int32_t ifbr_portno; /* member port number */ 193 u_int32_t ifbr_path_cost; /* member stp path cost */ 194}; 195 196/* ifbr_ifsflags flags about interfaces */ 197#define IFBIF_LEARNING 0x0001 /* ifs can learn */ 198#define IFBIF_DISCOVER 0x0002 /* sends packets w/unknown dst */ 199#define IFBIF_BLOCKNONIP 0x0004 /* ifs blocks non-IP/ARP in/out */ 200#define IFBIF_STP 0x0008 /* participate in spanning tree*/ 201#define IFBIF_SPAN 0x0100 /* ifs is a span port (ro) */ 202#define IFBIF_RO_MASK 0xff00 /* read only bits */ 203 204struct ifbifconf { 205 char ifbic_name[IFNAMSIZ]; /* bridge ifs name */ 206 u_int32_t ifbic_len; /* buffer size */ 207 union { 208 caddr_t ifbicu_buf; 209 struct ifbreq *ifbicu_req; 210 } ifbic_ifbicu; 211#define ifbic_buf ifbic_ifbicu.ifbicu_buf 212#define ifbic_req ifbic_ifbicu.ifbicu_req 213}; 214.Ed 215.It Dv SIOCBRDGADD Fa "struct ifbreq *" 216Add the interface named in 217.Va ifbr_ifsname 218to the bridge named in 219.Va ifbr_name . 220.It Dv SIOCBRDGDEL Fa "struct ifbreq *" 221Delete the interface named in 222.Va ifbr_ifsname 223from the bridge named in 224.Va ifbr_name . 225.It Dv SIOCBRDGADDS Fa "struct ifbreq *" 226Add the interface named in 227.Va ifbr_ifsname 228as a span port to the bridge named in 229.Va ifbr_name . 230.It Dv SIOCBRDGDELS Fa "struct ifbreq *" 231Delete the interface named in 232.Va ifbr_ifsname 233from the list of span ports of the bridge named in 234.Va ifbr_name . 235.It Dv SIOCBRDGSIFFLGS Fa "struct ifbreq *" 236Set the bridge member interface flags for the interface named in 237.Va ifbr_ifsname 238attached to the bridge 239.Va ifbr_name . 240If the flag 241.Dv IFBIF_LEARNING 242is set on an interface, source addresses from frames received on the 243interface are recorded in the address cache. 244If the flag 245.Dv IFBIF_DISCOVER 246is set, the interface will receive packets destined for unknown 247destinations, otherwise a frame that has a destination not found 248in the address cache is not forwarded to this interface. 249The default for newly added interfaces has both flags set. 250If the flag 251.Dv IFBIF_BLOCKNONIP 252is set, only 253.Xr ip 4 , 254.Xr ip6 4 , 255.Xr arp 4 , 256and 257Reverse ARP packets will be bridged from and to the interface. 258.It Dv SIOCBRDGGIFFLGS Fa "struct ifbreq *" 259Retrieve the bridge member interface flags for the interface named in 260.Va ifbr_ifsname 261attached to the bridge 262.Va ifbr_name . 263.It Dv SIOCBRDGRTS Fa "struct ifbaconf *" 264Retrieve the address cache of the bridge named in 265.Va ifbac_name . 266This request takes an 267.Vt ifbaconf 268structure (see below) as a value-result parameter. 269The 270.Va ifbac_len 271field should be initially set to the size of the buffer pointed to by 272.Va ifbac_buf . 273On return, it will contain the length, in bytes, of the configuration list. 274.Pp 275Alternatively, if the 276.Va ifbac_len 277passed in is set to 0, 278.Dv SIOCBRDGRTS 279will set it to the size that 280.Va ifbac_buf 281needs to be to fit the entire configuration list, and will not fill in the other 282parameters. 283As with 284.Dv SIOCBRDGIFS , 285this is useful for determining the exact size that 286.Va ifbac_buf 287needs to be in advance. 288.Pp 289The argument structure is defined as follows: 290.Bd -literal 291struct ifbareq { 292 char ifba_name[IFNAMSIZ]; /* bridge name */ 293 char ifba_ifsname[IFNAMSIZ];/* destination ifs */ 294 u_int8_t ifba_age; /* address age */ 295 u_int8_t ifba_flags; /* address flags */ 296 struct ether_addr ifba_dst; /* destination addr */ 297}; 298 299#define IFBAF_TYPEMASK 0x03 /* address type mask */ 300#define IFBAF_DYNAMIC 0x00 /* dynamically learned */ 301#define IFBAF_STATIC 0x01 /* static address */ 302 303struct ifbaconf { 304 char ifbac_name[IFNAMSIZ]; /* bridge ifs name */ 305 u_int32_t ifbac_len; /* buffer size */ 306 union { 307 caddr_t ifbacu_buf; /* buffer */ 308 struct ifbareq *ifbacu_req; /* request pointer */ 309 } ifbac_ifbacu; 310#define ifbac_buf ifbac_ifbacu.ifbacu_buf 311#define ifbac_req ifbac_ifbacu.ifbacu_req 312}; 313.Ed 314.Pp 315Address cache entries with the type set to 316.Dv IFBAF_DYNAMIC 317in 318.Va ifba_flags 319are entries learned by the bridge. 320Entries with the type set to 321.Dv IFBAF_STATIC 322are manually added entries. 323.It Dv SIOCBRDGSADDR Fa "struct ifbareq *" 324Add an entry, manually, to the address cache for the bridge named in 325.Va ifba_name . 326The address and its associated interface and flags are set in the 327.Va ifba_dst , 328.Va ifba_ifsname , 329and 330.Va ifba_flags 331fields, respectively. 332.It Dv SIOCBRDGDADDR Fa "struct ifbareq *" 333Delete an entry from the address cache of the bridge named in 334.Va ifba_name . 335Entries are deleted strictly based on the address field 336.Va ifba_dst . 337.It Dv SIOCBRDGFLUSH Fa "struct ifbreq *" 338Flush addresses from the cache. 339.Va ifbr_name 340contains the name of the bridge device, and 341.Va ifbr_ifsflags 342should be set to 343.Dv IFBF_FLUSHALL 344to flush all addresses from the cache or 345.Dv IFBF_FLUSHDYN 346to flush only the dynamically learned addresses from the cache. 347.It Dv SIOCBRDGSCACHE Fa "struct ifbrparam *" 348Set the maximum address cache size for the bridge named in 349.Va ifbrp_name 350to 351.Va ifbrp_csize 352entries. 353.Pp 354The argument structure is as follows: 355.Bd -literal 356struct ifbrparam { 357 char ifbrp_name[IFNAMSIZ]; 358 union { 359 u_int32_t ifbrpu_csize; /* cache size */ 360 int ifbrpu_ctime; /* cache time */ 361 u_int16_t ifbrpu_prio; /* bridge priority */ 362 u_int8_t ifbrpu_hellotime; /* hello time */ 363 u_int8_t ifbrpu_fwddelay; /* fwd delay */ 364 u_int8_t ifbrpu_maxage; /* max age */ 365 u_int64_t ifbrpu_datapath; /* datapath-id */ 366 u_int32_t ifbrpu_maxgroup; /* group size */ 367 } ifbrp_ifbrpu; 368}; 369#define ifbrp_csize ifbrp_ifbrpu.ifbrpu_csize 370#define ifbrp_ctime ifbrp_ifbrpu.ifbrpu_ctime 371#define ifbrp_prio ifbrp_ifbrpu.ifbrpu_prio 372#define ifbrp_hellotime ifbrp_ifbrpu.ifbrpu_hellotime 373#define ifbrp_fwddelay ifbrp_ifbrpu.ifbrpu_fwddelay 374#define ifbrp_maxage ifbrp_ifbrpu.ifbrpu_maxage 375#define ifbrp_datapath ifbrp_ifbrpu.ifbrpu_datapath 376#define ifbrp_maxflow ifbrp_ifbrpu.ifbrpu_csize 377#define ifbrp_maxgroup ifbrp_ifbrpu.ifbrpu_maxgroup 378.Ed 379.Pp 380Note that the 381.Va ifbrp_ctime , ifbrp_hellotime , ifbrp_fwddelay 382and 383.Va ifbrp_maxage 384fields are in seconds. 385.It Dv SIOCBRDGGCACHE Fa "struct ifbrparam *" 386Retrieve the maximum size of the address cache for the bridge 387.Va ifbrp_name . 388.It Dv SIOCBRDGSTO Fa "struct ifbrparam *" 389Set the time, in seconds, for how long addresses which have not been 390seen on the network (i.e., have not transmitted a packet) will remain in 391the cache to the value 392.Va ifbrp_ctime . 393If the time is set to zero, no aging is performed on the address cache. 394.It Dv SIOCBRDGGTO Fa "struct ifbrparam *" 395Retrieve the address cache expiration time (see above). 396.It Dv SIOCBRDGARL Fa "struct ifbrlreq *" 397Add an Ethernet address filtering rule to the bridge on a specific interface. 398.Va ifbr_name 399contains the name of the bridge device, and 400.Va ifbr_ifsname 401contains the name of the bridge member interface. 402.Pp 403Rules are applied in the order in which they were added to the bridge, 404and the first matching rule's action parameter determines the fate of 405the packet. 406The 407.Va ifbr_action 408field is one of 409.Dv BRL_ACTION_PASS 410or 411.Dv BRL_ACTION_BLOCK , 412to pass or block matching frames, respectively. 413The 414.Va ifbr_flags 415field specifies whether the rule should match on input, output, or both 416by using the flags 417.Dv BRL_FLAG_IN 418and 419.Dv BRL_FLAG_OUT . 420At least one of these flags must be set. 421.Pp 422The 423.Va ifbr_flags 424field 425also specifies whether either (or both) of the source and destination 426addresses should be matched by using the 427.Dv BRL_FLAG_SRCVALID 428and 429.Dv BRL_FLAG_DSTVALID 430flags. 431The 432.Va ifbr_src 433field is the source address that triggers the rule (only considered if 434.Va ifbr_flags 435has the 436.Dv BRL_FLAG_SRCVALID 437bit set). 438The 439.Va ifbr_src 440field is the destination address that triggers the rule (only considered if 441.Va ifbr_flags 442has the 443.Dv BRL_FLAG_DSTVALID 444bit set). 445If neither bit is set, the rule matches all frames. 446.Pp 447The argument structure is as follows: 448.Bd -literal 449struct ifbrlreq { 450 char ifbr_name[IFNAMSIZ]; /* bridge ifs name */ 451 char ifbr_ifsname[IFNAMSIZ]; /* member ifs name */ 452 u_int8_t ifbr_action; /* disposition */ 453 u_int8_t ifbr_flags; /* flags */ 454 struct ether_addr ifbr_src; /* source mac */ 455 struct ether_addr ifbr_dst; /* destination mac */ 456 char ifbr_tagname[PF_TAG_NAME_SIZE]; /* pf tagname */ 457}; 458#define BRL_ACTION_BLOCK 0x01 /* block frame */ 459#define BRL_ACTION_PASS 0x02 /* pass frame */ 460#define BRL_FLAG_IN 0x08 /* input rule */ 461#define BRL_FLAG_OUT 0x04 /* output rule */ 462#define BRL_FLAG_SRCVALID 0x02 /* src valid */ 463#define BRL_FLAG_DSTVALID 0x01 /* dst valid */ 464.Ed 465.It Dv SIOCBRDGFRL Fa "struct ifbrlreq *" 466Remove all filtering rules from a bridge interface member. 467.Va ifbr_name 468contains the name of the bridge device, and 469.Va ifbr_ifsname 470contains the name of the bridge member interface. 471.It Dv SIOCBRDGGRL Fa "struct ifbrlconf *" 472Retrieve all of the rules from the bridge, 473.Va ifbrl_name , 474for the member interface, 475.Va ifbrl_ifsname . 476This request takes an 477.Vt ifbrlconf 478structure (see below) as a value-result parameter. 479The 480.Va ifbrl_len 481field should be initially set to the size of the buffer pointed to by 482.Va ifbrl_buf . 483On return, it will contain the length, in bytes, of the configuration list. 484.Pp 485Alternatively, if the 486.Va ifbrl_len 487passed in is set to 0, 488.Dv SIOCBRDGGRL 489will set it to the size that 490.Va ifbrl_buf 491needs to be to fit the entire configuration list, and will not fill in the other 492parameters. 493As with 494.Dv SIOCBRDGIFS , 495this is useful for determining the exact size that 496.Va ifbrl_buf 497needs to be in advance. 498.Pp 499The argument structure is defined as follows: 500.Bd -literal 501struct ifbrlconf { 502 char ifbrl_name[IFNAMSIZ]; /* bridge ifs name */ 503 char ifbrl_ifsname[IFNAMSIZ]; /* member ifs name */ 504 u_int32_t ifbrl_len; /* buffer size */ 505 union { 506 caddr_t ifbrlu_buf; 507 struct ifbrlreq *ifbrlu_req; 508 } ifbrl_ifbrlu; 509#define ifbrl_buf ifbrl_ifbrlu.ifbrlu_buf 510#define ifbrl_req ifbrl_ifbrlu.ifbrlu_req 511}; 512.Ed 513.\" .It Dv SIOCBRDGGSIFS Fa "struct ifbreq *" 514.It Dv SIOCBRDGGPRI Fa "struct ifbrparam *" 515Retrieve the Spanning Tree Protocol (STP) priority parameter of the bridge into 516the 517.Va ifbrp_prio 518field. 519.It Dv SIOCBRDGSPRI Fa "struct ifbrparam *" 520Set the STP priority parameter of the bridge to the value in 521.Va ifbrp_prio . 522.It Dv SIOCBRDGGHT Fa "struct ifbrparam *" 523Retrieve the STP hello time parameter, in seconds, of the bridge into the 524.Va ifbrp_hellotime 525field. 526.It Dv SIOCBRDGSHT Fa "struct ifbrparam *" 527Set the STP hello time parameter, in seconds, of the bridge to the value in 528.Va ifbrp_hellotime . 529The value in 530.Va ifbrp_hellotime 531cannot be zero. 532.It Dv SIOCBRDGGFD Fa "struct ifbrparam *" 533Retrieve the STP forward delay parameter, in seconds, of the bridge into the 534.Va ifbrp_fwddelay 535field. 536.It Dv SIOCBRDGSFD Fa "struct ifbrparam *" 537Set the STP forward delay parameter, in seconds, of the bridge to the value in 538.Va ifbrp_fwddelay . 539The value in 540.Va ifbrp_fwddelay 541cannot be zero. 542.It Dv SIOCBRDGGMA Fa "struct ifbrparam *" 543Retrieve the STP maximum age parameter, in seconds, of the bridge into the 544.Va ifbrp_maxage 545field. 546.It Dv SIOCBRDGSMA Fa "struct ifbrparam *" 547Set the STP maximum age parameter, in seconds, of the bridge to the value in 548.Va ifbrp_maxage . 549The value in 550.Va ifbrp_maxage 551cannot be zero. 552.It Dv SIOCBRDGSIFPRIO Fa "struct ifbreq *" 553Set the STP priority parameter of the interface named in 554.Va ifbr_ifsname 555to the value in 556.Va ifbr_priority . 557.It Dv SIOCBRDGSIFCOST Fa "struct ifbreq *" 558Set the STP cost parameter of the interface named in 559.Va ifbr_ifsname 560to the value in 561.Va ifbr_path_cost . 562The value in 563.Va ifbr_path_cost 564must be greater than or equal to one. 565.El 566.Sh ERRORS 567If the 568.Xr ioctl 2 569call fails, 570.Xr errno 2 571is set to one of the following values: 572.Bl -tag -width Er 573.It Bq Er ENOENT 574For an add request, this means that the named interface is not configured 575into the system. 576For a delete operation, it means that the named interface is not a member 577of the bridge. 578For an address cache deletion, the address was not found in the table. 579.It Bq Er ENOMEM 580Memory could not be allocated for an interface or cache entry 581to be added to the bridge. 582.It Bq Er EEXIST 583The named interface is already a member of the bridge. 584.It Bq Er EBUSY 585The named interface is already a member of another bridge. 586.It Bq Er EINVAL 587The named interface is not an Ethernet interface, or an invalid ioctl 588was performed on the bridge. 589.It Bq Er ENETDOWN 590Address cache operation (flush, add, or delete) on a bridge that is 591in the down state. 592.It Bq Er EPERM 593Super-user privilege is required to add and delete interfaces to and from 594bridges and to set the bridge interface flags. 595.It Bq Er EFAULT 596The buffer used in a 597.Dv SIOCBRDGIFS 598or 599.Dv SIOCBRDGRTS 600request points outside of the process's allocated address space. 601.It Bq Er ESRCH 602No such member interface in the bridge. 603.El 604.Sh NOTES 605Bridged packets pass through 606.Xr pf 4 607filters once as input on the receiving interface and once 608as output on all interfaces on which they are forwarded. 609In order to pass through the bridge packets must pass 610any 611.Ar in 612rules on the input and any 613.Ar out 614rules on the output interface. 615Packets may be blocked either entering or leaving the bridge. 616.Pp 617Return packets generated by pf itself are not routed using the 618kernel routing table. 619Instead, pf will send these replies back to the same Ethernet 620address that the original packet came from. 621This applies to rules with 622.Ic return , 623.Ic return-rst , 624.Ic return-icmp , 625.Ic return-icmp6 , 626or 627.Ic synproxy 628defined. 629At the moment, only 630.Ic return-rst 631on IPv4 is implemented and the other packet generating rules 632are unsupported. 633.Pp 634If an IP packet is too large for the outgoing interface, the bridge 635will perform IP fragmentation. 636This can happen when bridge members 637have different MTUs or when IP fragments are reassembled by pf. 638Non-IP packets which are too large for the outgoing interface will be 639dropped. 640.Pp 641If the 642.Dv IFF_LINK2 643flag is set on the 644.Nm 645interface, the bridge will also perform transparent 646.Xr ipsec 4 647processing on the packets (encrypt or decrypt them), according to the 648policies set with the 649.Xr ipsecctl 8 650command by the administrator. 651If appropriate security associations (SAs) do not exist, any key 652management daemons such as 653.Xr isakmpd 8 654that are running on the bridge will be invoked to establish the 655necessary SAs. 656These daemons have to be configured as if they were running on the 657host whose traffic they are protecting (i.e., they need to have the 658appropriate authentication and authorization material, such as keys 659and certificates, to impersonate the protected host(s)). 660.Sh SEE ALSO 661.Xr errno 2 , 662.Xr ioctl 2 , 663.Xr arp 4 , 664.Xr etherip 4 , 665.Xr ip 4 , 666.Xr ip6 4 , 667.Xr ipsec 4 , 668.Xr netintro 4 , 669.Xr pf 4 , 670.Xr switch 4 , 671.Xr vether 4 , 672.Xr hostname.if 5 , 673.Xr ifconfig 8 , 674.Xr ipsecctl 8 , 675.Xr isakmpd 8 , 676.Xr netstart 8 677.Sh HISTORY 678The 679.Nm 680kernel interface first appeared in 681.Ox 2.5 . 682.Sh AUTHORS 683The 684.Nm 685kernel interface was written by 686.An Jason L. Wright Aq Mt jason@thought.net 687as part of an undergraduate independent study at the 688University of North Carolina at Greensboro. 689.Pp 690Support for rapid spanning tree reconfigurations (RSTP) was added by 691.An Andrew Thompson Aq Mt thompsa@freebsd.org 692and ported to 693.Ox 694by 695.An Reyk Floeter Aq Mt reyk@openbsd.org . 696.Sh BUGS 697There are some rather special network interface chipsets which will 698not work in a bridge configuration. 699Some chipsets have serious flaws when running in promiscuous mode, like the 700TI ThunderLAN (see 701.Xr tl 4 ) , 702which receives its own transmissions (this renders the address learning 703cache useless). 704Most other chipsets work fine though. 705