1.\" -*- Nroff -*- 2.\" Copyright 1996, 1997 Massachusetts Institute of Technology 3.\" 4.\" Permission to use, copy, modify, and distribute this software and 5.\" its documentation for any purpose and without fee is hereby 6.\" granted, provided that both the above copyright notice and this 7.\" permission notice appear in all copies, that both the above 8.\" copyright notice and this permission notice appear in all 9.\" supporting documentation, and that the name of M.I.T. not be used 10.\" in advertising or publicity pertaining to distribution of the 11.\" software without specific, written prior permission. M.I.T. makes 12.\" no representations about the suitability of this software for any 13.\" purpose. It is provided "as is" without express or implied 14.\" warranty. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS 17.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE, 18.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 19.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT 20.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 23.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 24.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 25.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 26.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd March 22, 2017 32.Dt IFNET 9 33.Os 34.Sh NAME 35.Nm ifnet , 36.Nm ifaddr , 37.Nm ifqueue , 38.Nm if_data 39.Nd kernel interfaces for manipulating network interfaces 40.Sh SYNOPSIS 41.In sys/param.h 42.In sys/time.h 43.In sys/socket.h 44.In net/if.h 45.In net/if_var.h 46.In net/if_types.h 47.\" 48.Ss "Interface Manipulation Functions" 49.Ft "struct ifnet *" 50.Fn if_alloc "u_char type" 51.Ft void 52.Fn if_attach "struct ifnet *ifp" 53.Ft void 54.Fn if_detach "struct ifnet *ifp" 55.Ft void 56.Fn if_free "struct ifnet *ifp" 57.Ft void 58.Fn if_free_type "struct ifnet *ifp" "u_char type" 59.Ft void 60.Fn if_down "struct ifnet *ifp" 61.Ft int 62.Fn ifioctl "struct socket *so" "u_long cmd" "caddr_t data" "struct thread *td" 63.Ft int 64.Fn ifpromisc "struct ifnet *ifp" "int pswitch" 65.Ft int 66.Fn if_allmulti "struct ifnet *ifp" "int amswitch" 67.Ft "struct ifnet *" 68.Fn ifunit "const char *name" 69.Ft "struct ifnet *" 70.Fn ifunit_ref "const char *name" 71.Ft void 72.Fn if_up "struct ifnet *ifp" 73.\" 74.Ss "Interface Address Functions" 75.Ft "struct ifaddr *" 76.Fn ifaddr_byindex "u_short idx" 77.Ft "struct ifaddr *" 78.Fn ifa_ifwithaddr "struct sockaddr *addr" 79.Ft "struct ifaddr *" 80.Fn ifa_ifwithdstaddr "struct sockaddr *addr" "int fib" 81.Ft "struct ifaddr *" 82.Fn ifa_ifwithnet "struct sockaddr *addr" "int ignore_ptp" "int fib" 83.Ft "struct ifaddr *" 84.Fn ifaof_ifpforaddr "struct sockaddr *addr" "struct ifnet *ifp" 85.Ft void 86.Fn ifa_ref "struct ifaddr *ifa" 87.Ft void 88.Fn ifa_free "struct ifaddr *ifa" 89.\" 90.Ss "Interface Multicast Address Functions" 91.Ft int 92.Fn if_addmulti "struct ifnet *ifp" "struct sockaddr *sa" "struct ifmultiaddr **ifmap" 93.Ft int 94.Fn if_delmulti "struct ifnet *ifp" "struct sockaddr *sa" 95.Ft "struct ifmultiaddr *" 96.Fn if_findmulti "struct ifnet *ifp" "struct sockaddr *sa" 97.Ss "Output queue macros" 98.Fn IF_DEQUEUE "struct ifqueue *ifq" "struct mbuf *m" 99.\" 100.Ss "struct ifnet Member Functions" 101.Ft void 102.Fn \*(lp*if_input\*(rp "struct ifnet *ifp" "struct mbuf *m" 103.Ft int 104.Fo \*(lp*if_output\*(rp 105.Fa "struct ifnet *ifp" "struct mbuf *m" 106.Fa "const struct sockaddr *dst" "struct route *ro" 107.Fc 108.Ft void 109.Fn \*(lp*if_start\*(rp "struct ifnet *ifp" 110.Ft int 111.Fn \*(lp*if_transmit\*(rp "struct ifnet *ifp" "struct mbuf *m" 112.Ft void 113.Fn \*(lp*if_qflush\*(rp "struct ifnet *ifp" 114.Ft int 115.Fn \*(lp*if_ioctl\*(rp "struct ifnet *ifp" "u_long cmd" "caddr_t data" 116.Ft void 117.Fn \*(lp*if_init\*(rp "void *if_softc" 118.Ft int 119.Fo \*(lp*if_resolvemulti\*(rp 120.Fa "struct ifnet *ifp" "struct sockaddr **retsa" "struct sockaddr *addr" 121.Fc 122.Ss "struct ifaddr member function" 123.Ft void 124.Fo \*(lp*ifa_rtrequest\*(rp 125.Fa "int cmd" "struct rtentry *rt" "struct rt_addrinfo *info" 126.Fc 127.\" 128.Ss "Global Variables" 129.Vt extern struct ifnethead ifnet ; 130.\" extern struct ifindex_entry *ifindex_table ; 131.Vt extern int if_index ; 132.Vt extern int ifqmaxlen ; 133.Sh DATA STRUCTURES 134The kernel mechanisms for handling network interfaces reside primarily 135in the 136.Vt ifnet , if_data , ifaddr , 137and 138.Vt ifmultiaddr 139structures in 140.In net/if.h 141and 142.In net/if_var.h 143and the functions named above and defined in 144.Pa /sys/net/if.c . 145Those interfaces which are intended to be used by user programs 146are defined in 147.In net/if.h ; 148these include the interface flags, the 149.Vt if_data 150structure, and the structures defining the appearance of 151interface-related messages on the 152.Xr route 4 153routing socket and in 154.Xr sysctl 3 . 155The header file 156.In net/if_var.h 157defines the kernel-internal interfaces, including the 158.Vt ifnet , ifaddr , 159and 160.Vt ifmultiaddr 161structures and the functions which manipulate them. 162(A few user programs will need 163.In net/if_var.h 164because it is the prerequisite of some other header file like 165.In netinet/if_ether.h . 166Most references to those two files in particular can be replaced by 167.In net/ethernet.h . ) 168.Pp 169The system keeps a linked list of interfaces using the 170.Li TAILQ 171macros defined in 172.Xr queue 3 ; 173this list is headed by a 174.Vt "struct ifnethead" 175called 176.Va ifnet . 177The elements of this list are of type 178.Vt "struct ifnet" , 179and most kernel routines which manipulate interface as such accept or 180return pointers to these structures. 181Each interface structure 182contains an 183.Vt if_data 184structure used for statistics and information. 185Each interface also has a 186.Li TAILQ 187of interface addresses, described by 188.Vt ifaddr 189structures. 190An 191.Dv AF_LINK 192address 193(see 194.Xr link_addr 3 ) 195describing the link layer implemented by the interface (if any) 196is accessed by the 197.Fn ifaddr_byindex 198function or 199.Va if_addr 200structure. 201(Some trivial interfaces do not provide any link layer addresses; 202this structure, while still present, serves only to identify the 203interface name and index.) 204.Pp 205Finally, those interfaces supporting reception of multicast datagrams 206have a 207.Li TAILQ 208of multicast group memberships, described by 209.Vt ifmultiaddr 210structures. 211These memberships are reference-counted. 212.Pp 213Interfaces are also associated with an output queue, defined as a 214.Vt "struct ifqueue" ; 215this structure is used to hold packets while the interface is in the 216process of sending another. 217.Pp 218.Ss The ifnet Structure 219The fields of 220.Vt "struct ifnet" 221are as follows: 222.Bl -tag -width ".Va if_capabilities" -offset indent 223.It Va if_softc 224.Pq Vt "void *" 225A pointer to the driver's private state block. 226(Initialized by driver.) 227.It Va if_l2com 228.Pq Vt "void *" 229A pointer to the common data for the interface's layer 2 protocol. 230(Initialized by 231.Fn if_alloc . ) 232.It Va if_vnet 233.Pq Vt "struct vnet *" 234A pointer to the virtual network stack instance. 235(Initialized by 236.Fn if_attach . ) 237.It Va if_home_vnet 238.Pq Vt "struct vnet *" 239A pointer to the parent virtual network stack, where this 240.Vt "struct ifnet" 241originates from. 242(Initialized by 243.Fn if_attach . ) 244.It Va if_link 245.Pq Fn TAILQ_ENTRY ifnet 246.Xr queue 3 247macro glue. 248.It Va if_xname 249.Pq Vt "char *" 250The name of the interface, 251(e.g., 252.Dq Li fxp0 253or 254.Dq Li lo0 ) . 255(Initialized by driver 256(usually via 257.Fn if_initname ) . ) 258.It Va if_dname 259.Pq Vt "const char *" 260The name of the driver. 261(Initialized by driver 262(usually via 263.Fn if_initname ) . ) 264.It Va if_dunit 265.Pq Vt int 266A unique number assigned to each interface managed by a particular 267driver. 268Drivers may choose to set this to 269.Dv IF_DUNIT_NONE 270if a unit number is not associated with the device. 271(Initialized by driver 272(usually via 273.Fn if_initname ) . ) 274.It Va if_refcount 275.Pq Vt u_int 276The reference count. 277(Initialized by 278.Fn if_alloc . ) 279.It Va if_addrhead 280.Pq Vt "struct ifaddrhead" 281The head of the 282.Xr queue 3 283.Li TAILQ 284containing the list of addresses assigned to this interface. 285.It Va if_pcount 286.Pq Vt int 287A count of promiscuous listeners on this interface, used to 288reference-count the 289.Dv IFF_PROMISC 290flag. 291.It Va if_carp 292.Pq Vt "struct carp_if *" 293A pointer to the CARP interface structure, 294.Xr carp 4 . 295(Initialized by the driver-specific 296.Fn if_ioctl 297routine.) 298.It Va if_bpf 299.Pq Vt "struct bpf_if *" 300Opaque per-interface data for the packet filter, 301.Xr bpf 4 . 302(Initialized by 303.Fn bpf_attach . ) 304.It Va if_index 305.Pq Vt u_short 306A unique number assigned to each interface in sequence as it is 307attached. 308This number can be used in a 309.Vt "struct sockaddr_dl" 310to refer to a particular interface by index 311(see 312.Xr link_addr 3 ) . 313(Initialized by 314.Fn if_alloc . ) 315.It Va if_vlantrunk 316.Pq Vt struct ifvlantrunk * 317A pointer to 802.1Q trunk structure, 318.Xr vlan 4 . 319(Initialized by the driver-specific 320.Fn if_ioctl 321routine.) 322.It Va if_flags 323.Pq Vt int 324Flags describing operational parameters of this interface (see below). 325(Manipulated by generic code.) 326.It Va if_drv_flags 327.Pq Vt int 328Flags describing operational status of this interface (see below). 329(Manipulated by driver.) 330.It Va if_capabilities 331.Pq Vt int 332Flags describing the capabilities the interface supports (see below). 333.It Va if_capenable 334.Pq Vt int 335Flags describing the enabled capabilities of the interface (see below). 336.It Va if_linkmib 337.Pq Vt "void *" 338A pointer to an interface-specific MIB structure exported by 339.Xr ifmib 4 . 340(Initialized by driver.) 341.It Va if_linkmiblen 342.Pq Vt size_t 343The size of said structure. 344(Initialized by driver.) 345.It Va if_data 346.Pq Vt "struct if_data" 347More statistics and information; see 348.Sx "The if_data structure" , 349below. 350(Initialized by driver, manipulated by both driver and generic 351code.) 352.It Va if_multiaddrs 353.Pq Vt struct ifmultihead 354The head of the 355.Xr queue 3 356.Li TAILQ 357containing the list of multicast addresses assigned to this interface. 358.It Va if_amcount 359.Pq Vt int 360A number of multicast requests on this interface, used to 361reference-count the 362.Dv IFF_ALLMULTI 363flag. 364.It Va if_addr 365.Pq Vt "struct ifaddr *" 366A pointer to the link-level interface address. 367(Initialized by 368.Fn if_alloc . ) 369.\" .It Va if_llsoftc 370.\" .Pq Vt "void *" 371.\" The purpose of the field is unclear. 372.It Va if_snd 373.Pq Vt "struct ifaltq" 374The output queue. 375(Manipulated by driver.) 376.It Va if_broadcastaddr 377.Pq Vt "const u_int8_t *" 378A link-level broadcast bytestring for protocols with variable address 379length. 380.It Va if_bridge 381.Pq Vt "void *" 382A pointer to the bridge interface structure, 383.Xr if_bridge 4 . 384(Initialized by the driver-specific 385.Fn if_ioctl 386routine.) 387.It Va if_label 388.Pq Vt "struct label *" 389A pointer to the MAC Framework label structure, 390.Xr mac 4 . 391(Initialized by 392.Fn if_alloc . ) 393.It Va if_afdata 394.Pq Vt "void *" 395An address family dependent data region. 396.It Va if_afdata_initialized 397.Pq Vt int 398Used to track the current state of address family initialization. 399.It Va if_afdata_lock 400.Pq Vt "struct rwlock" 401An 402.Xr rwlock 9 403lock used to protect 404.Va if_afdata 405internals. 406.It Va if_linktask 407.Pq Vt "struct task" 408A 409.Xr taskqueue 9 410task scheduled for link state change events of the interface. 411.It Va if_addr_lock 412.Pq Vt "struct rwlock" 413An 414.Xr rwlock 9 415lock used to protect interface-related address lists. 416.It Va if_clones 417.Pq Fn LIST_ENTRY ifnet 418.Xr queue 3 419macro glue for the list of clonable network interfaces. 420.It Va if_groups 421.Pq Fn TAILQ_HEAD "" "ifg_list" 422The head of the 423.Xr queue 3 424.Li TAILQ 425containing the list of groups per interface. 426.It Va if_pf_kif 427.Pq Vt "void *" 428A pointer to the structure used for interface abstraction by 429.Xr pf 4 . 430.It Va if_lagg 431.Pq Vt "void *" 432A pointer to the 433.Xr lagg 4 434interface structure. 435.It Va if_alloctype 436.Pq Vt u_char 437The type of the interface as it was at the time of its allocation. 438It is used to cache the type passed to 439.Fn if_alloc , 440but unlike 441.Va if_type , 442it would not be changed by drivers. 443.El 444.Pp 445References to 446.Vt ifnet 447structures are gained by calling the 448.Fn if_ref 449function and released by calling the 450.Fn if_rele 451function. 452They are used to allow kernel code walking global interface lists 453to release the 454.Vt ifnet 455lock yet keep the 456.Vt ifnet 457structure stable. 458.Pp 459There are in addition a number of function pointers which the driver 460must initialize to complete its interface with the generic interface 461layer: 462.Bl -ohang -offset indent 463.It Fn if_input 464Pass a packet to an appropriate upper layer as determined 465from the link-layer header of the packet. 466This routine is to be called from an interrupt handler or 467used to emulate reception of a packet on this interface. 468A single function implementing 469.Fn if_input 470can be shared among multiple drivers utilizing the same link-layer 471framing, e.g., Ethernet. 472.It Fn if_output 473Output a packet on interface 474.Fa ifp , 475or queue it on the output queue if the interface is already active. 476.It Fn if_transmit 477Transmit a packet on an interface or queue it if the interface is 478in use. 479This function will return 480.Dv ENOBUFS 481if the devices software and hardware queues are both full. 482This function must be installed after 483.Fn if_attach 484to override the default implementation. 485This function is exposed in order to allow drivers to manage their own queues 486and to reduce the latency caused by a frequently gratuitous enqueue / dequeue 487pair to ifq. 488The suggested internal software queuing mechanism is buf_ring. 489.It Fn if_qflush 490Free mbufs in internally managed queues when the interface is marked down. 491This function must be installed after 492.Fn if_attach 493to override the default implementation. 494This function is exposed in order to allow drivers to manage their own queues 495and to reduce the latency caused by a frequently gratuitous enqueue / dequeue 496pair to ifq. 497The suggested internal software queuing mechanism is buf_ring. 498.It Fn if_start 499Start queued output on an interface. 500This function is exposed in 501order to provide for some interface classes to share a 502.Fn if_output 503among all drivers. 504.Fn if_start 505may only be called when the 506.Dv IFF_DRV_OACTIVE 507flag is not set. 508(Thus, 509.Dv IFF_DRV_OACTIVE 510does not literally mean that output is active, but rather that the 511device's internal output queue is full.) Please note that this function 512will soon be deprecated. 513.It Fn if_ioctl 514Process interface-related 515.Xr ioctl 2 516requests 517(defined in 518.In sys/sockio.h ) . 519Preliminary processing is done by the generic routine 520.Fn ifioctl 521to check for appropriate privileges, locate the interface being 522manipulated, and perform certain generic operations like twiddling 523flags and flushing queues. 524See the description of 525.Fn ifioctl 526below for more information. 527.It Fn if_init 528Initialize and bring up the hardware, 529e.g., reset the chip and enable the receiver unit. 530Should mark the interface running, 531but not active 532.Dv ( IFF_DRV_RUNNING , ~IIF_DRV_OACTIVE ) . 533.It Fn if_resolvemulti 534Check the requested multicast group membership, 535.Fa addr , 536for validity, and if necessary compute a link-layer group which 537corresponds to that address which is returned in 538.Fa *retsa . 539Returns zero on success, or an error code on failure. 540.El 541.Ss "Interface Flags" 542Interface flags are used for a number of different purposes. 543Some 544flags simply indicate information about the type of interface and its 545capabilities; others are dynamically manipulated to reflect the 546current state of the interface. 547Flags of the former kind are marked 548.Aq S 549in this table; the latter are marked 550.Aq D . 551Flags which begin with 552.Dq IFF_DRV_ 553are stored in 554.Va if_drv_flags ; 555all other flags are stored in 556.Va if_flags . 557.Pp 558The macro 559.Dv IFF_CANTCHANGE 560defines the bits which cannot be set by a user program using the 561.Dv SIOCSIFFLAGS 562command to 563.Xr ioctl 2 ; 564these are indicated by an asterisk 565.Pq Ql * 566in the following listing. 567.Pp 568.Bl -tag -width ".Dv IFF_POINTOPOINT" -offset indent -compact 569.It Dv IFF_UP 570.Aq D 571The interface has been configured up by the user-level code. 572.It Dv IFF_BROADCAST 573.Aq S* 574The interface supports broadcast. 575.It Dv IFF_DEBUG 576.Aq D 577Used to enable/disable driver debugging code. 578.It Dv IFF_LOOPBACK 579.Aq S 580The interface is a loopback device. 581.It Dv IFF_POINTOPOINT 582.Aq S* 583The interface is point-to-point; 584.Dq broadcast 585address is actually the address of the other end. 586.It Dv IFF_DRV_RUNNING 587.Aq D* 588The interface has been configured and dynamic resources were 589successfully allocated. 590Probably only useful internal to the 591interface. 592.It Dv IFF_NOARP 593.Aq D 594Disable network address resolution on this interface. 595.It Dv IFF_PROMISC 596.Aq D* 597This interface is in promiscuous mode. 598.It Dv IFF_PPROMISC 599.Aq D 600This interface is in the permanently promiscuous mode (implies 601.Dv IFF_PROMISC ) . 602.It Dv IFF_ALLMULTI 603.Aq D* 604This interface is in all-multicasts mode (used by multicast routers). 605.It Dv IFF_DRV_OACTIVE 606.Aq D* 607The interface's hardware output queue (if any) is full; output packets 608are to be queued. 609.It Dv IFF_SIMPLEX 610.Aq S* 611The interface cannot hear its own transmissions. 612.It Dv IFF_LINK0 613.It Dv IFF_LINK1 614.It Dv IFF_LINK2 615.Aq D 616Control flags for the link layer. 617(Currently abused to select among 618multiple physical layers on some devices.) 619.It Dv IFF_MULTICAST 620.Aq S* 621This interface supports multicast. 622.It Dv IFF_CANTCONFIG 623.Aq S* 624The interface is not configurable in a meaningful way. 625Primarily useful for 626.Dv IFT_USB 627interfaces registered at the interface list. 628.It Dv IFF_MONITOR 629.Aq D 630This interface blocks transmission of packets and discards incoming 631packets after BPF processing. 632Used to monitor network traffic but not interact 633with the network in question. 634.It Dv IFF_STATICARP 635.Aq D 636Used to enable/disable ARP requests on this interface. 637.It Dv IFF_DYING 638.Aq D* 639Set when the 640.Vt ifnet 641structure of this interface is being released and still has 642.Va if_refcount 643references. 644.It Dv IFF_RENAMING 645.Aq D 646Set when this interface is being renamed. 647.El 648.Ss "Interface Capabilities Flags" 649Interface capabilities are specialized features an interface may 650or may not support. 651These capabilities are very hardware-specific 652and allow, when enabled, 653to offload specific network processing to the interface 654or to offer a particular feature for use by other kernel parts. 655.Pp 656It should be stressed that a capability can be completely 657uncontrolled (i.e., stay always enabled with no way to disable it) 658or allow limited control over itself (e.g., depend on another 659capability's state.) 660Such peculiarities are determined solely by the hardware and driver 661of a particular interface. 662Only the driver possesses 663the knowledge on whether and how the interface capabilities 664can be controlled. 665Consequently, capabilities flags in 666.Va if_capenable 667should never be modified directly by kernel code other than 668the interface driver. 669The command 670.Dv SIOCSIFCAP 671to 672.Fn ifioctl 673is the dedicated means to attempt altering 674.Va if_capenable 675on an interface. 676Userland code shall use 677.Xr ioctl 2 . 678.Pp 679The following capabilities are currently supported by the system: 680.Bl -tag -width ".Dv IFCAP_POLLING_NOCOUNT" -offset indent 681.It Dv IFCAP_RXCSUM 682This interface can do checksum validation on receiving data. 683Some interfaces do not have sufficient buffer storage to store frames 684above a certain MTU-size completely. 685The driver for the interface might disable hardware checksum validation 686if the MTU is set above the hardcoded limit. 687.It Dv IFCAP_TXCSUM 688This interface can do checksum calculation on transmitting data. 689.It Dv IFCAP_HWCSUM 690A shorthand for 691.Pq Dv IFCAP_RXCSUM | IFCAP_TXCSUM . 692.It Dv IFCAP_NETCONS 693This interface can be a network console. 694.It Dv IFCAP_VLAN_MTU 695The 696.Xr vlan 4 697driver can operate over this interface in software tagging mode 698without having to decrease MTU on 699.Xr vlan 4 700interfaces below 1500 bytes. 701This implies the ability of this interface to cope with frames somewhat 702longer than permitted by the Ethernet specification. 703.It Dv IFCAP_VLAN_HWTAGGING 704This interface can do VLAN tagging on output and 705demultiplex frames by their VLAN tag on input. 706.It Dv IFCAP_JUMBO_MTU 707This Ethernet interface can transmit and receive frames up to 7089000 bytes long. 709.It Dv IFCAP_POLLING 710This interface supports 711.Xr polling 4 . 712See below for details. 713.It Dv IFCAP_VLAN_HWCSUM 714This interface can do checksum calculation on both transmitting 715and receiving data on 716.Xr vlan 4 717interfaces (implies 718.Dv IFCAP_HWCSUM ) . 719.It Dv IFCAP_TSO4 720This Ethernet interface supports TCP4 Segmentation offloading. 721.It Dv IFCAP_TSO6 722This Ethernet interface supports TCP6 Segmentation offloading. 723.It Dv IFCAP_TSO 724A shorthand for 725.Pq Dv IFCAP_TSO4 | IFCAP_TSO6 . 726.It Dv IFCAP_TOE4 727This Ethernet interface supports TCP offloading. 728.It Dv IFCAP_TOE6 729This Ethernet interface supports TCP6 offloading. 730.It Dv IFCAP_TOE 731A shorthand for 732.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 . 733.It Dv IFCAP_WOL_UCAST 734This Ethernet interface supports waking up on any Unicast packet. 735.It Dv IFCAP_WOL_MCAST 736This Ethernet interface supports waking up on any Multicast packet. 737.It Dv IFCAP_WOL_MAGIC 738This Ethernet interface supports waking up on any Magic packet such 739as those sent by 740.Xr wake 8 . 741.It Dv IFCAP_WOL 742A shorthand for 743.Pq Dv IFCAP_WOL_UCAST | IFCAP_WOL_MCAST | IFCAP_WOL_MAGIC . 744.It Dv IFCAP_TOE4 745This Ethernet interface supports TCP4 Offload Engine. 746.It Dv IFCAP_TOE6 747This Ethernet interface supports TCP6 Offload Engine. 748.It Dv IFCAP_TOE 749A shorthand for 750.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 . 751.It Dv IFCAP_VLAN_HWFILTER 752This interface supports frame filtering in hardware on 753.Xr vlan 4 754interfaces. 755.It Dv IFCAP_POLLING_NOCOUNT 756The return value for the number of processed packets should be 757skipped for this interface. 758.It Dv IFCAP_VLAN_HWTSO 759This interface supports TCP Segmentation offloading on 760.Xr vlan 4 761interfaces (implies 762.Dv IFCAP_TSO ) . 763.It Dv IFCAP_LINKSTATE 764This Ethernet interface supports dynamic link state changes. 765.El 766.Pp 767The ability of advanced network interfaces to offload certain 768computational tasks from the host CPU to the board is limited 769mostly to TCP/IP. 770Therefore a separate field associated with an interface 771(see 772.Va ifnet.if_data.ifi_hwassist 773below) 774keeps a detailed description of its enabled capabilities 775specific to TCP/IP processing. 776The TCP/IP module consults the field to see which tasks 777can be done on an 778.Em outgoing 779packet by the interface. 780The flags defined for that field are a superset of those for 781.Va mbuf.m_pkthdr.csum_flags , 782namely: 783.Bl -tag -width ".Dv CSUM_FRAGMENT" -offset indent 784.It Dv CSUM_IP 785The interface will compute IP checksums. 786.It Dv CSUM_TCP 787The interface will compute TCP checksums. 788.It Dv CSUM_UDP 789The interface will compute UDP checksums. 790.El 791.Pp 792An interface notifies the TCP/IP module about the tasks 793the former has performed on an 794.Em incoming 795packet by setting the corresponding flags in the field 796.Va mbuf.m_pkthdr.csum_flags 797of the 798.Vt mbuf chain 799containing the packet. 800See 801.Xr mbuf 9 802for details. 803.Pp 804The capability of a network interface to operate in 805.Xr polling 4 806mode involves several flags in different 807global variables and per-interface fields. 808The capability flag 809.Dv IFCAP_POLLING 810set in interface's 811.Va if_capabilities 812indicates support for 813.Xr polling 4 814on the particular interface. 815If set in 816.Va if_capabilities , 817the same flag can be marked or cleared in the interface's 818.Va if_capenable 819within 820.Fn ifioctl , 821thus initiating switch of the interface to 822.Xr polling 4 823mode or interrupt 824mode, respectively. 825The actual mode change is managed by the driver-specific 826.Fn if_ioctl 827routine. 828The 829.Xr polling 4 830handler returns the number of packets processed. 831.Ss The if_data Structure 832The 833.Vt if_data 834structure contains statistics and identifying information used 835by management programs, and which is exported to user programs by way 836of the 837.Xr ifmib 4 838branch of the 839.Xr sysctl 3 840MIB. 841The following elements of the 842.Vt if_data 843structure are initialized by the interface and are not expected to change 844significantly over the course of normal operation: 845.Bl -tag -width ".Va ifi_lastchange" -offset indent 846.It Va ifi_type 847.Pq Vt u_char 848The type of the interface, as defined in 849.In net/if_types.h 850and described below in the 851.Sx "Interface Types" 852section. 853.It Va ifi_physical 854.Pq Vt u_char 855Intended to represent a selection of physical layers on devices which 856support more than one; never implemented. 857.It Va ifi_addrlen 858.Pq Vt u_char 859Length of a link-layer address on this device, or zero if there are 860none. 861Used to initialized the address length field in 862.Vt sockaddr_dl 863structures referring to this interface. 864.It Va ifi_hdrlen 865.Pq Vt u_char 866Maximum length of any link-layer header which might be prepended by 867the driver to a packet before transmission. 868The generic code computes 869the maximum over all interfaces and uses that value to influence the 870placement of data in 871.Vt mbuf Ns s 872to attempt to ensure that there is always 873sufficient space to prepend a link-layer header without allocating an 874additional 875.Vt mbuf . 876.It Va ifi_datalen 877.Pq Vt u_char 878Length of the 879.Vt if_data 880structure. 881Allows some stabilization of the routing socket ABI in the face of 882increases in the length of 883.Vt struct ifdata . 884.It Va ifi_mtu 885.Pq Vt u_long 886The maximum transmission unit of the medium, exclusive of any 887link-layer overhead. 888.It Va ifi_metric 889.Pq Vt u_long 890A dimensionless metric interpreted by a user-mode routing process. 891.It Va ifi_baudrate 892.Pq Vt u_long 893The line rate of the interface, in bits per second. 894.It Va ifi_hwassist 895.Pq Vt u_long 896A detailed interpretation of the capabilities 897to offload computational tasks for 898.Em outgoing 899packets. 900The interface driver must keep this field in accord with 901the current value of 902.Va if_capenable . 903.It Va ifi_epoch 904.Pq Vt time_t 905The system uptime when interface was attached or the statistics 906below were reset. 907This is intended to be used to set the SNMP variable 908.Va ifCounterDiscontinuityTime . 909It may also be used to determine if two successive queries for an 910interface of the same index have returned results for the same 911interface. 912.El 913.Pp 914The structure additionally contains generic statistics applicable to a 915variety of different interface types (except as noted, all members are 916of type 917.Vt u_long ) : 918.Bl -tag -width ".Va ifi_lastchange" -offset indent 919.It Va ifi_link_state 920.Pq Vt u_char 921The current link state of Ethernet interfaces. 922See the 923.Sx Interface Link States 924section for possible values. 925.It Va ifi_ipackets 926Number of packets received. 927.It Va ifi_ierrors 928Number of receive errors detected (e.g., FCS errors, DMA overruns, 929etc.). 930More detailed breakdowns can often be had by way of a 931link-specific MIB. 932.It Va ifi_opackets 933Number of packets transmitted. 934.It Va ifi_oerrors 935Number of output errors detected (e.g., late collisions, DMA overruns, 936etc.). 937More detailed breakdowns can often be had by way of a 938link-specific MIB. 939.It Va ifi_collisions 940Total number of collisions detected on output for CSMA interfaces. 941(This member is sometimes [ab]used by other types of interfaces for 942other output error counts.) 943.It Va ifi_ibytes 944Total traffic received, in bytes. 945.It Va ifi_obytes 946Total traffic transmitted, in bytes. 947.It Va ifi_imcasts 948Number of packets received which were sent by link-layer multicast. 949.It Va ifi_omcasts 950Number of packets sent by link-layer multicast. 951.It Va ifi_iqdrops 952Number of packets dropped on input. 953Rarely implemented. 954.It Va ifi_oqdrops 955Number of packets dropped on output. 956.It Va ifi_noproto 957Number of packets received for unknown network-layer protocol. 958.It Va ifi_lastchange 959.Pq Vt "struct timeval" 960The time of the last administrative change to the interface (as required 961for 962.Tn SNMP ) . 963.El 964.Ss Interface Types 965The header file 966.In net/if_types.h 967defines symbolic constants for a number of different types of 968interfaces. 969The most common are: 970.Pp 971.Bl -tag -offset indent -width ".Dv IFT_PROPVIRTUAL" -compact 972.It Dv IFT_OTHER 973none of the following 974.It Dv IFT_ETHER 975Ethernet 976.It Dv IFT_ISO88023 977ISO 8802-3 CSMA/CD 978.It Dv IFT_ISO88024 979ISO 8802-4 Token Bus 980.It Dv IFT_ISO88025 981ISO 8802-5 Token Ring 982.It Dv IFT_ISO88026 983ISO 8802-6 DQDB MAN 984.It Dv IFT_FDDI 985FDDI 986.It Dv IFT_PPP 987Internet Point-to-Point Protocol 988.Pq Xr ppp 8 989.It Dv IFT_LOOP 990The loopback 991.Pq Xr lo 4 992interface 993.It Dv IFT_SLIP 994Serial Line IP 995.It Dv IFT_PARA 996Parallel-port IP 997.Pq Dq Tn PLIP 998.It Dv IFT_ATM 999Asynchronous Transfer Mode 1000.It Dv IFT_USB 1001USB Interface 1002.El 1003.Ss Interface Link States 1004The following link states are currently defined: 1005.Pp 1006.Bl -tag -offset indent -width ".Dv LINK_STATE_UNKNOWN" -compact 1007.It Dv LINK_STATE_UNKNOWN 1008The link is in an invalid or unknown state. 1009.It Dv LINK_STATE_DOWN 1010The link is down. 1011.It Dv LINK_STATE_UP 1012The link is up. 1013.El 1014.Ss The ifaddr Structure 1015Every interface is associated with a list 1016(or, rather, a 1017.Li TAILQ ) 1018of addresses, rooted at the interface structure's 1019.Va if_addrhead 1020member. 1021The first element in this list is always an 1022.Dv AF_LINK 1023address representing the interface itself; multi-access network 1024drivers should complete this structure by filling in their link-layer 1025addresses after calling 1026.Fn if_attach . 1027Other members of the structure represent network-layer addresses which 1028have been configured by means of the 1029.Dv SIOCAIFADDR 1030command to 1031.Xr ioctl 2 , 1032called on a socket of the appropriate protocol family. 1033The elements of this list consist of 1034.Vt ifaddr 1035structures. 1036Most protocols will declare their own protocol-specific 1037interface address structures, but all begin with a 1038.Vt "struct ifaddr" 1039which provides the most-commonly-needed functionality across all 1040protocols. 1041Interface addresses are reference-counted. 1042.Pp 1043The members of 1044.Vt "struct ifaddr" 1045are as follows: 1046.Bl -tag -width ".Va ifa_rtrequest" -offset indent 1047.It Va ifa_addr 1048.Pq Vt "struct sockaddr *" 1049The local address of the interface. 1050.It Va ifa_dstaddr 1051.Pq Vt "struct sockaddr *" 1052The remote address of point-to-point interfaces, and the broadcast 1053address of broadcast interfaces. 1054.Va ( ifa_broadaddr 1055is a macro for 1056.Va ifa_dstaddr . ) 1057.It Va ifa_netmask 1058.Pq Vt "struct sockaddr *" 1059The network mask for multi-access interfaces, and the confusion 1060generator for point-to-point interfaces. 1061.It Va ifa_ifp 1062.Pq Vt "struct ifnet *" 1063A link back to the interface structure. 1064.It Va ifa_link 1065.Pq Fn TAILQ_ENTRY ifaddr 1066.Xr queue 3 1067glue for list of addresses on each interface. 1068.It Va ifa_rtrequest 1069See below. 1070.It Va ifa_flags 1071.Pq Vt u_short 1072Some of the flags which would be used for a route representing this 1073address in the route table. 1074.It Va ifa_refcnt 1075.Pq Vt short 1076The reference count. 1077.El 1078.Pp 1079References to 1080.Vt ifaddr 1081structures are gained by calling the 1082.Fn ifa_ref 1083function and released by calling the 1084.Fn ifa_free 1085function. 1086.Pp 1087.Fn ifa_rtrequest 1088is a pointer to a function which receives callouts from the routing 1089code 1090.Pq Fn rtrequest 1091to perform link-layer-specific actions upon requests to add, 1092or delete routes. 1093The 1094.Fa cmd 1095argument indicates the request in question: 1096.Dv RTM_ADD , 1097or 1098.Dv RTM_DELETE . 1099The 1100.Fa rt 1101argument is the route in question; the 1102.Fa info 1103argument contains the specific destination being manipulated. 1104.Sh FUNCTIONS 1105The functions provided by the generic interface code can be divided 1106into two groups: those which manipulate interfaces, and those which 1107manipulate interface addresses. 1108In addition to these functions, there 1109may also be link-layer support routines which are used by a number of 1110drivers implementing a specific link layer over different hardware; 1111see the documentation for that link layer for more details. 1112.Ss The ifmultiaddr Structure 1113Every multicast-capable interface is associated with a list of 1114multicast group memberships, which indicate at a low level which 1115link-layer multicast addresses (if any) should be accepted, and at a 1116high level, in which network-layer multicast groups a user process has 1117expressed interest. 1118.Pp 1119The elements of the structure are as follows: 1120.Bl -tag -width ".Va ifma_refcount" -offset indent 1121.It Va ifma_link 1122.Pq Fn LIST_ENTRY ifmultiaddr 1123.Xr queue 3 1124macro glue. 1125.It Va ifma_addr 1126.Pq Vt "struct sockaddr *" 1127A pointer to the address which this record represents. 1128The 1129memberships for various address families are stored in arbitrary 1130order. 1131.It Va ifma_lladdr 1132.Pq Vt "struct sockaddr *" 1133A pointer to the link-layer multicast address, if any, to which the 1134network-layer multicast address in 1135.Va ifma_addr 1136is mapped, else a null pointer. 1137If this element is non-nil, this 1138membership also holds an invisible reference to another membership for 1139that link-layer address. 1140.It Va ifma_refcount 1141.Pq Vt u_int 1142A reference count of requests for this particular membership. 1143.El 1144.Ss Interface Manipulation Functions 1145.Bl -ohang -offset indent 1146.It Fn if_alloc 1147Allocate and initialize 1148.Vt "struct ifnet" . 1149Initialization includes the allocation of an interface index and may 1150include the allocation of a 1151.Fa type 1152specific structure in 1153.Va if_l2com . 1154.It Fn if_attach 1155Link the specified interface 1156.Fa ifp 1157into the list of network interfaces. 1158Also initialize the list of 1159addresses on that interface, and create a link-layer 1160.Vt ifaddr 1161structure to be the first element in that list. 1162(A pointer to 1163this address structure is saved in the 1164.Vt ifnet 1165structure and is accessed by the 1166.Fn ifaddr_byindex 1167function.) 1168The 1169.Fa ifp 1170must have been allocated by 1171.Fn if_alloc . 1172.It Fn if_detach 1173Shut down and unlink the specified 1174.Fa ifp 1175from the interface list. 1176.It Fn if_free 1177Free the given 1178.Fa ifp 1179back to the system. 1180The interface must have been previously detached if it was ever attached. 1181.It Fn if_free_type 1182Identical to 1183.Fn if_free 1184except that the given 1185.Fa type 1186is used to free 1187.Va if_l2com 1188instead of the type in 1189.Va if_type . 1190This is intended for use with drivers that change their interface type. 1191.It Fn if_down 1192Mark the interface 1193.Fa ifp 1194as down (i.e., 1195.Dv IFF_UP 1196is not set), 1197flush its output queue, notify protocols of the transition, 1198and generate a message from the 1199.Xr route 4 1200routing socket. 1201.It Fn if_up 1202Mark the interface 1203.Fa ifp 1204as up, notify protocols of the transition, 1205and generate a message from the 1206.Xr route 4 1207routing socket. 1208.It Fn ifpromisc 1209Add or remove a promiscuous reference to 1210.Fa ifp . 1211If 1212.Fa pswitch 1213is true, add a reference; 1214if it is false, remove a reference. 1215On reference count transitions 1216from zero to one and one to zero, set the 1217.Dv IFF_PROMISC 1218flag appropriately and call 1219.Fn if_ioctl 1220to set up the interface in the desired mode. 1221.It Fn if_allmulti 1222As 1223.Fn ifpromisc , 1224but for the all-multicasts 1225.Pq Dv IFF_ALLMULTI 1226flag instead of the promiscuous flag. 1227.It Fn ifunit 1228Return an 1229.Vt ifnet 1230pointer for the interface named 1231.Fa name . 1232.It Fn ifunit_ref 1233Return a reference-counted (via 1234.Fn ifa_ref ) 1235.Vt ifnet 1236pointer for the interface named 1237.Fa name . 1238This is the preferred function over 1239.Fn ifunit . 1240The caller is responsible for releasing the reference with 1241.Fn if_rele 1242when it is finished with the ifnet. 1243.It Fn ifioctl 1244Process the ioctl request 1245.Fa cmd , 1246issued on socket 1247.Fa so 1248by thread 1249.Fa td , 1250with data parameter 1251.Fa data . 1252This is the main routine for handling all interface configuration 1253requests from user mode. 1254It is ordinarily only called from the socket-layer 1255.Xr ioctl 2 1256handler, and only for commands with class 1257.Sq Li i . 1258Any unrecognized commands will be passed down to socket 1259.Fa so Ns 's 1260protocol for 1261further interpretation. 1262The following commands are handled by 1263.Fn ifioctl : 1264.Pp 1265.Bl -tag -width ".Dv SIOCGIFNETMASK" -offset indent -compact 1266.It Dv SIOCGIFCONF 1267Get interface configuration. 1268(No call-down to driver.) 1269.Pp 1270.It Dv SIOCSIFNAME 1271Set the interface name. 1272.Dv RTM_IFANNOUNCE 1273departure and arrival messages are sent so that 1274routing code that relies on the interface name will update its interface 1275list. 1276Caller must have appropriate privilege. 1277(No call-down to driver.) 1278.It Dv SIOCGIFCAP 1279.It Dv SIOCGIFFIB 1280.It Dv SIOCGIFFLAGS 1281.It Dv SIOCGIFMETRIC 1282.It Dv SIOCGIFMTU 1283.It Dv SIOCGIFPHYS 1284Get interface capabilities, FIB, flags, metric, MTU, medium selection. 1285(No call-down to driver.) 1286.Pp 1287.It Dv SIOCSIFCAP 1288Enable or disable interface capabilities. 1289Caller must have appropriate privilege. 1290Before a call to the driver-specific 1291.Fn if_ioctl 1292routine, the requested mask for enabled capabilities is checked 1293against the mask of capabilities supported by the interface, 1294.Va if_capabilities . 1295Requesting to enable an unsupported capability is invalid. 1296The rest is supposed to be done by the driver, 1297which includes updating 1298.Va if_capenable 1299and 1300.Va if_data.ifi_hwassist 1301appropriately. 1302.Pp 1303.It Dv SIOCSIFFIB 1304Sets interface FIB. 1305Caller must have appropriate privilege. 1306FIB values start at 0 and values greater or equals than 1307.Va net.fibs 1308are considered invalid. 1309.It Dv SIOCSIFFLAGS 1310Change interface flags. 1311Caller must have appropriate privilege. 1312If a change to the 1313.Dv IFF_UP 1314flag is requested, 1315.Fn if_up 1316or 1317.Fn if_down 1318is called as appropriate. 1319Flags listed in 1320.Dv IFF_CANTCHANGE 1321are masked off, and the field 1322.Va if_flags 1323in the interface structure is updated. 1324Finally, the driver 1325.Fn if_ioctl 1326routine is called to perform any setup 1327requested. 1328.Pp 1329.It Dv SIOCSIFMETRIC 1330.It Dv SIOCSIFPHYS 1331Change interface metric or medium. 1332Caller must have appropriate privilege. 1333.Pp 1334.It Dv SIOCSIFMTU 1335Change interface MTU. 1336Caller must have appropriate privilege. 1337MTU 1338values less than 72 or greater than 65535 are considered invalid. 1339The driver 1340.Fn if_ioctl 1341routine is called to implement the change; it is responsible for any 1342additional sanity checking and for actually modifying the MTU in the 1343interface structure. 1344.Pp 1345.It Dv SIOCADDMULTI 1346.It Dv SIOCDELMULTI 1347Add or delete permanent multicast group memberships on the interface. 1348Caller must have appropriate privilege. 1349The 1350.Fn if_addmulti 1351or 1352.Fn if_delmulti 1353function is called to perform the operation; qq.v. 1354.Pp 1355.It Dv SIOCAIFADDR 1356.It Dv SIOCDIFADDR 1357The socket's protocol control routine is called to implement the 1358requested action. 1359.El 1360.El 1361.Pp 1362.Fn if_down , 1363.Fn ifioctl , 1364.Fn ifpromisc , 1365and 1366.Fn if_up 1367must be called at 1368.Fn splnet 1369or higher. 1370.Ss "Interface Address Functions" 1371Several functions exist to look up an interface address structure 1372given an address. 1373.Fn ifa_ifwithaddr 1374returns an interface address with either a local address or a 1375broadcast address precisely matching the parameter 1376.Fa addr . 1377.Fn ifa_ifwithdstaddr 1378returns an interface address for a point-to-point interface whose 1379remote 1380.Pq Dq destination 1381address is 1382.Fa addr 1383and a fib is 1384.Fa fib . 1385If 1386.Fa fib 1387is 1388.Dv RT_ALL_FIBS , 1389then the first interface address matching 1390.Fa addr 1391will be returned. 1392.Pp 1393.Fn ifa_ifwithnet 1394returns the most specific interface address which matches the 1395specified address, 1396.Fa addr , 1397subject to its configured netmask, or a point-to-point interface 1398address whose remote address is 1399.Fa addr 1400if one is found. 1401If 1402.Fa ignore_ptp 1403is true, skip point-to-point interface addresses. 1404The 1405.Fa fib 1406parameter is handled the same way as by 1407.Fn ifa_ifwithdstaddr . 1408.Pp 1409.Fn ifaof_ifpforaddr 1410returns the most specific address configured on interface 1411.Fa ifp 1412which matches address 1413.Fa addr , 1414subject to its configured netmask. 1415If the interface is 1416point-to-point, only an interface address whose remote address is 1417precisely 1418.Fa addr 1419will be returned. 1420.Pp 1421.Fn ifaddr_byindex 1422returns the link-level address of the interface with the given index 1423.Fa idx . 1424.Pp 1425All of these functions return a null pointer if no such address can be 1426found. 1427.Ss "Interface Multicast Address Functions" 1428The 1429.Fn if_addmulti , 1430.Fn if_delmulti , 1431and 1432.Fn if_findmulti 1433functions provide support for requesting and relinquishing multicast 1434group memberships, and for querying an interface's membership list, 1435respectively. 1436The 1437.Fn if_addmulti 1438function takes a pointer to an interface, 1439.Fa ifp , 1440and a generic address, 1441.Fa sa . 1442It also takes a pointer to a 1443.Vt "struct ifmultiaddr *" 1444which is filled in on successful return with the address of the 1445group membership control block. 1446The 1447.Fn if_addmulti 1448function performs the following four-step process: 1449.Bl -enum -offset indent 1450.It 1451Call the interface's 1452.Fn if_resolvemulti 1453entry point to determine the link-layer address, if any, corresponding 1454to this membership request, and also to give the link layer an 1455opportunity to veto this membership request should it so desire. 1456.It 1457Check the interface's group membership list for a pre-existing 1458membership for this group. 1459If one is not found, allocate a new one; 1460if one is, increment its reference count. 1461.It 1462If the 1463.Fn if_resolvemulti 1464routine returned a link-layer address corresponding to the group, 1465repeat the previous step for that address as well. 1466.It 1467If the interface's multicast address filter needs to be changed 1468because a new membership was added, call the interface's 1469.Fn if_ioctl 1470routine 1471(with a 1472.Fa cmd 1473argument of 1474.Dv SIOCADDMULTI ) 1475to request that it do so. 1476.El 1477.Pp 1478The 1479.Fn if_delmulti 1480function, given an interface 1481.Fa ifp 1482and an address, 1483.Fa sa , 1484reverses this process. 1485Both functions return zero on success, or a 1486standard error number on failure. 1487.Pp 1488The 1489.Fn if_findmulti 1490function examines the membership list of interface 1491.Fa ifp 1492for an address matching 1493.Fa sa , 1494and returns a pointer to that 1495.Vt "struct ifmultiaddr" 1496if one is found, else it returns a null pointer. 1497.Sh SEE ALSO 1498.Xr ioctl 2 , 1499.Xr link_addr 3 , 1500.Xr queue 3 , 1501.Xr sysctl 3 , 1502.Xr bpf 4 , 1503.Xr ifmib 4 , 1504.Xr lo 4 , 1505.Xr netintro 4 , 1506.Xr polling 4 , 1507.Xr config 8 , 1508.Xr ppp 8 , 1509.Xr mbuf 9 , 1510.Xr rtentry 9 1511.Rs 1512.%A Gary R. Wright 1513.%A W. Richard Stevens 1514.%B TCP/IP Illustrated 1515.%V Vol. 2 1516.%O Addison-Wesley, ISBN 0-201-63354-X 1517.Re 1518.Sh AUTHORS 1519This manual page was written by 1520.An Garrett A. Wollman . 1521