--- name: "ifaddr" section: "9" platform: "linux" package: "freebsd-manpages" version: "6.0-5" release: "Debian 4.0 (Etch)" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/ifaddr" --- # ifaddr(9) kernel interfaces for manipulating network interfaces ## NAME **ifnet**, **ifaddr**, **ifqueue**, **if\_data** – kernel interfaces for manipulating network interfaces ## SYNOPSIS **#include \** **#include \** **#include \** **#include \** **#include \** **#include \** ### Interface Manipulation Functions *struct ifnet \**\ **if\_alloc**(*u\_char type*); *void*\ **if\_attach**(*struct ifnet \*ifp*); *void*\ **if\_detach**(*struct ifnet \*ifp*); *void*\ **if\_free**(*struct ifnet \*ifp*); *void*\ **if\_free\_type**(*struct ifnet \*ifp*, *u\_char type*); *void*\ **if\_down**(*struct ifnet \*ifp*); *int*\ **ifioctl**(*struct socket \*so*, *u\_long cmd*, *caddr\_t data*, *struct thread \*td*); *int*\ **ifpromisc**(*struct ifnet \*ifp*, *int pswitch*); *int*\ **if\_allmulti**(*struct ifnet \*ifp*, *int amswitch*); *struct ifnet \**\ **ifunit**(*const char \*name*); *void*\ **if\_up**(*struct ifnet \*ifp*); ### Interface Address Functions *struct ifaddr \**\ **ifa\_ifwithaddr**(*struct sockaddr \*addr*); *struct ifaddr \**\ **ifa\_ifwithdstaddr**(*struct sockaddr \*addr*); *struct ifaddr \**\ **ifa\_ifwithnet**(*struct sockaddr \*addr*); *struct ifaddr \**\ **ifaof\_ifpforaddr**(*struct sockaddr \*addr*, *struct ifnet \*ifp*); *void*\ **ifafree**(*struct ifaddr \*ifa*); **IFAFREE**(*struct ifaddr \*ifa*); ### Interface Multicast Address Functions *int*\ **if\_addmulti**(*struct ifnet \*ifp*, *struct sockaddr \*sa*, *struct ifmultiaddr \*\*ifmap*); *int*\ **if\_delmulti**(*struct ifnet \*ifp*, *struct sockaddr \*sa*); *struct ifmultiaddr \**\ **ifmaof\_ifpforaddr**(*struct sockaddr \*addr*, *struct ifnet \*ifp*); ### Output queue macros **IF\_DEQUEUE**(*struct ifqueue \*ifq*, *struct mbuf \*m*); ### struct ifnet Member Functions *void*\ **\*if\_input**(*struct ifnet \*ifp*, *struct mbuf \*m*); *int*\ **\*if\_output**(*struct ifnet \*ifp*, *struct mbuf \*m*, *struct sockaddr \*dst*, *struct rtentry \*rt*); *void*\ **\*if\_start**(*struct ifnet \*ifp*); *int*\ **\*if\_done**(*struct ifnet \*ifp*); *int*\ **\*if\_ioctl**(*struct ifnet \*ifp*, *int cmd*, *caddr\_t data*); *void*\ **\*if\_watchdog**(*struct ifnet \*ifp*); *int*\ **\*if\_poll\_recv**(*struct ifnet \*ifp*, *int \*quotap*); *int*\ **\*if\_poll\_xmit**(*struct ifnet \*ifp*, *int \*quotap*); *void*\ **\*if\_poll\_inttrn**(*struct ifnet \*ifp*); *void*\ **\*if\_poll\_slowinput**(*struct ifnet \*ifp*, *struct mbuf \*m*); *void*\ **\*if\_init**(*void \*if\_softc*); *int*\ **\*if\_resolvemulti**(*struct ifnet \*ifp*, *struct sockaddr \*\*retsa*, *struct sockaddr \*addr*); ### struct ifaddr member function *void*\ **\*ifa\_rtrequest**(*int cmd*, *struct rtentry \*rt*, *struct sockaddr \*dst*); ### Global Variables *extern* *struct* *ifnethead* *ifnet*; *extern* *struct* *ifaddr* *\*\*ifnet\_addrs*; *extern* *int* *if\_index*; *extern* *int* *ifqmaxlen*; ## DATA STRUCTURES The kernel mechanisms for handling network interfaces reside primarily in the *ifnet*, *if\_data*, *ifaddr*, and *ifmultiaddr* structures in ⟨net/if.h⟩ and ⟨net/if\_var.h⟩ and the functions named above and defined in */sys/net/if.c*. Those interfaces which are intended to be used by user programs are defined in ⟨net/if.h⟩; these include the interface flags, the *if\_data* structure, and the structures defining the appearance of interface-related messages on the [route(4)](/route/4.md) routing socket and in [sysctl(3)](/sysctl/3.md). The header file ⟨net/if\_var.h⟩ defines the kernel-internal interfaces, including the *ifnet*, *ifaddr*, and *ifmultiaddr* structures and the functions which manipulate them. (A few user programs will need ⟨net/if\_var.h⟩ because it is the prerequisite of some other header file like ⟨netinet/if\_ether.h⟩. Most references to those two files in particular can be replaced by ⟨net/ethernet.h⟩.) The system keeps a linked list of interfaces using the TAILQ macros defined in [queue(3)](/queue/3.md); this list is headed by a *struct ifnethead* called *ifnet*. The elements of this list are of type *struct ifnet*, and most kernel routines which manipulate interface as such accept or return pointers to these structures. Each interface structure contains an *if\_data* structure, which contains statistics and identifying information used by management programs, and which is exported to user programs by way of the [ifmib(4)](/ifmib/4.md) branch of the [sysctl(3)](/sysctl/3.md) MIB. Each interface also has a TAILQ of interface addresses, described by *ifaddr* structures; the head of the queue is always an AF\_LINK address (see [link\_addr(3)](/link_addr/3.md)) describing the link layer implemented by the interface (if any). (Some trivial interfaces do not provide any link layer addresses; this structure, while still present, serves only to identify the interface name and index.) Finally, those interfaces supporting reception of multicast datagrams have a TAILQ of multicast group memberships, described by *ifmultiaddr* structures. These memberships are reference-counted. Interfaces are also associated with an output queue, defined as a *struct ifqueue*; this structure is used to hold packets while the interface is in the process of sending another. ### The Vt ifnet Ss structure The fields of *struct ifnet* are as follows: - *if\_softc* (*void \**) A pointer to the driver's private state block. (Initialized by driver.) - *if\_l2com* (*void \**) A pointer to the common data for the interface's layer 2 protocol. (Initialized by **if\_alloc**().) - *if\_link* (**TAILQ\_ENTRY**(*ifnet*)) [queue(3)](/queue/3.md) macro glue. - *if\_xname* (*char \**) The name of the interface, (e.g., “fxp0” or “lo0”). (Initialized by driver.) - *if\_dname* (*const char \**) The name of the driver. (Initialized by driver.) - *if\_dunit* (*int*) A unique number assigned to each interface managed by a particular driver. Drivers may choose to set this to IF\_DUNIT\_NONE if a unit number is not associated with the device. (Initialized by driver.) - *if\_addrhead* (*struct ifaddrhead*) The head of the [queue(3)](/queue/3.md) TAILQ containing the list of addresses assigned to this interface. - *if\_pcount* (*int*) A count of promiscuous listeners on this interface, used to reference-count the IFF\_PROMISC flag. - *if\_bpf* (*struct bpf\_if \**) Opaque per-interface data for the packet filter, [bpf(4)](/bpf/4.md). (Initialized by **bpf\_attach**().) - *if\_index* (*u\_short*) A unique number assigned to each interface in sequence as it is attached. This number can be used in a *struct sockaddr\_dl* to refer to a particular interface by index (see [link\_addr(3)](/link_addr/3.md)). (Initialized by **if\_alloc**().) - *if\_timer* (*short*) Number of seconds until the watchdog timer **if\_watchdog**() is called, or zero if the timer is disabled. (Set by driver, decremented by generic watchdog code.) - *if\_flags* (*int*) Flags describing operational parameters of this interface (see below). (Manipulated by both driver and generic code.) - *if\_capabilities* (*int*) Flags describing the capabilities the interface supports (see below). - *if\_capenable* (*int*) Flags describing the enabled capabilities of the interface (see below). - *if\_linkmib* (*void \**) A pointer to an interface-specific MIB structure exported by [ifmib(4)](/ifmib/4.md). (Initialized by driver.) - *if\_linkmiblen* (*size\_t*) The size of said structure. (Initialized by driver.) - *if\_data* (*struct if\_data*) More statistics and information; see The if\_data structure, below. (Initialized by driver, manipulated by both driver and generic code.) - *if\_snd* (*struct ifqueue*) The output queue. (Manipulated by driver.) There are in addition a number of function pointers which the driver must initialize to complete its interface with the generic interface layer: - **if\_input**() Pass a packet to an appropriate upper layer as determined from the link-layer header of the packet. This routine is to be called from an interrupt handler or used to emulate reception of a packet on this interface. A single function implementing **if\_input**() can be shared among multiple drivers utilizing the same link-layer framing, e.g., Ethernet. - **if\_output**() Output a packet on interface *ifp*, or queue it on the output queue if the interface is already active. - **if\_start**() Start queued output on an interface. This function is exposed in order to provide for some interface classes to share a **if\_output**() among all drivers. **if\_start**() may only be called when the IFF\_OACTIVE flag is not set. (Thus, IFF\_OACTIVE does not literally mean that output is active, but rather that the device's internal output queue is full.) - **if\_done**() Not used. We are not even sure what it was ever for. The prototype is faked. - **if\_ioctl**() Process interface-related [ioctl(2)](/ioctl/2.md) requests (defined in ⟨sys/sockio.h⟩). Preliminary processing is done by the generic routine **ifioctl**() to check for appropriate privileges, locate the interface being manipulated, and perform certain generic operations like twiddling flags and flushing queues. See the description of **ifioctl**() below for more information. - **if\_watchdog**() Routine called by the generic code when the watchdog timer, *if\_timer*, expires. Usually this will reset the interface. - **if\_init**() Initialize and bring up the hardware, e.g., reset the chip and the watchdog timer and enable the receiver unit. Should mark the interface running, but not active (IFF\_RUNNING, ~IIF\_OACTIVE). - **if\_resolvemulti**() Check the requested multicast group membership, *addr*, for validity, and if necessary compute a link-layer group which corresponds to that address which is returned in *\*retsa*. Returns zero on success, or an error code on failure. ### Interface Flags Interface flags are used for a number of different purposes. Some flags simply indicate information about the type of interface and its capabilities; others are dynamically manipulated to reflect the current state of the interface. Flags of the former kind are marked ⟨S⟩ in this table; the latter are marked ⟨D⟩. The macro IFF\_CANTCHANGE defines the bits which cannot be set by a user program using the SIOCSIFFLAGS command to [ioctl(2)](/ioctl/2.md); these are indicated by an asterisk (‘\*’) in the following listing. - IFF\_UP ⟨D⟩ The interface has been configured up by the user-level code. - IFF\_BROADCAST ⟨S\*⟩ The interface supports broadcast. - IFF\_DEBUG ⟨D⟩ Used to enable/disable driver debugging code. - IFF\_LOOPBACK ⟨S⟩ The interface is a loopback device. - IFF\_POINTOPOINT ⟨S\*⟩ The interface is point-to-point; “broadcast” address is actually the address of the other end. - IFF\_RUNNING ⟨D\*⟩ The interface has been configured and dynamic resources were successfully allocated. Probably only useful internal to the interface. - IFF\_NOARP ⟨D⟩ Disable network address resolution on this interface. - IFF\_PROMISC ⟨D\*⟩ This interface is in promiscuous mode. - IFF\_PPROMISC ⟨D⟩ This interface is in the permanently promiscuous mode (implies IFF\_PROMISC). - IFF\_ALLMULTI ⟨D\*⟩ This interface is in all-multicasts mode (used by multicast routers). - IFF\_OACTIVE ⟨D\*⟩ The interface's hardware output queue (if any) is full; output packets are to be queued. - IFF\_SIMPLEX ⟨S\*⟩ The interface cannot hear its own transmissions. - IFF\_LINK0 - IFF\_LINK1 - IFF\_LINK2 ⟨D⟩ Control flags for the link layer. (Currently abused to select among multiple physical layers on some devices.) - IFF\_MULTICAST ⟨S\*⟩ This interface supports multicast. - IFF\_POLLING ⟨D\*⟩ The interface is in [polling(4)](/polling/4.md) mode. See Interface Capabilities Flags for details. ### Interface Capabilities Flags Interface capabilities are specialized features an interface may or may not support. These capabilities are very hardware-specific and allow, when enabled, to offload specific network processing to the interface or to offer a particular feature for use by other kernel parts. It should be stressed that a capability can be completely uncontrolled (i.e., stay always enabled with no way to disable it) or allow limited control over itself (e.g., depend on another capability's state.) Such peculiarities are determined solely by the hardware and driver of a particular interface. Only the driver possesses the knowledge on whether and how the interface capabilities can be controlled. Consequently, capabilities flags in *if\_capenable* should never be modified directly by kernel code other than the interface driver. The command SIOCSIFCAP to **ifioctl**() is the dedicated means to attempt altering *if\_capenable* on an interface. Userland code shall use [ioctl(2)](/ioctl/2.md). The following capabilities are currently supported by the system: - IFCAP\_NETCONS This interface can be a network console. - IFCAP\_POLLING This interface supports [polling(4)](/polling/4.md). See below for details. - IFCAP\_RXCSUM This interface can do checksum validation on receiving data. Some interfaces do not have sufficient buffer storage to store frames above a certain MTU-size completely. The driver for the interface might disable hardware checksum validation if the MTU is set above the hardcoded limit. - IFCAP\_TXCSUM This interface can do checksum calculation on transmitting data. - IFCAP\_HWCSUM A shorthand for (IFCAP\_RXCSUM \| IFCAP\_TXCSUM). - IFCAP\_VLAN\_HWTAGGING This interface can do VLAN tagging on output and demultiplex frames by their VLAN tag on input. - IFCAP\_VLAN\_MTU The [vlan(4)](/vlan/4.md) driver can operate over this interface in software tagging mode without having to decrease MTU on [vlan(4)](/vlan/4.md) interfaces below 1500 bytes. This implies the ability of this interface to cope with frames somewhat longer than permitted by the Ethernet specification. - IFCAP\_JUMBO\_MTU This Ethernet interface can transmit and receive frames up to 9000 bytes long. The ability of advanced network interfaces to offload certain computational tasks from the host CPU to the board is limited mostly to TCP/IP. Therefore a separate field associated with an interface (see *ifnet.if\_data.ifi\_hwassist* below) keeps a detailed description of its enabled capabilities specific to TCP/IP processing. The TCP/IP module consults the field to see which tasks can be done on an *outgoing* packet by the interface. The flags defined for that field are a superset of those for *mbuf.m\_pkthdr.csum\_flags*, namely: - CSUM\_IP The interface will compute IP checksums. - CSUM\_TCP The interface will compute TCP checksums. - CSUM\_UDP The interface will compute UDP checksums. - CSUM\_IP\_FRAGS The interface can compute a TCP or UDP checksum for a packet fragmented by the host CPU. Makes sense only along with CSUM\_TCP or CSUM\_UDP. - CSUM\_FRAGMENT The interface will do the fragmentation of IP packets if necessary. The host CPU does not need to care about MTU on this interface as long as a packet to transmit through it is an IP one and it does not exceed the size of the hardware buffer. An interface notifies the TCP/IP module about the tasks the former has performed on an *incoming* packet by setting the corresponding flags in the field *mbuf.m\_pkthdr.csum\_flags* of the *mbuf* *chain* containing the packet. See [mbuf(9)](/mbuf/9.md) for details. The capability of a network interface to operate in [polling(4)](/polling/4.md) mode involves several flags in different global variables and per-interface fields. First, there is a system-wide [sysctl(8)](/sysctl/8.md) master switch named *kern.polling.enable*, which can toggle [polling(4)](/polling/4.md) globally. If that variable is set to non-zero, [polling(4)](/polling/4.md) will be used on those devices where it is enabled individually. Otherwise, [polling(4)](/polling/4.md) will not be used in the system. Second, the capability flag IFCAP\_POLLING set in interface's *if\_capabilities* indicates support for [polling(4)](/polling/4.md) on the particular interface. If set in *if\_capabilities*, the same flag can be marked or cleared in the interface's *if\_capenable*, thus initiating switch of the interface to [polling(4)](/polling/4.md) mode or interrupt mode, respectively. The actual mode change will occur at an implementation-specific moment in the future, e.g., during the next interrupt or [polling(4)](/polling/4.md) cycle. And finally, if the mode transition has been successful, the flag IFF\_POLLING is marked or cleared in the interface's *if\_flags* to indicate the current mode of the interface. ### The Vt if\_data Ss Structure In 4.4BSD, a subset of the interface information believed to be of interest to management stations was segregated from the *ifnet* structure and moved into its own *if\_data* structure to facilitate its use by user programs. The following elements of the *if\_data* structure are initialized by the interface and are not expected to change significantly over the course of normal operation: - *ifi\_type* (*u\_char*) The type of the interface, as defined in ⟨net/if\_types.h⟩ and described below in the Interface Types section. - *ifi\_physical* (*u\_char*) Intended to represent a selection of physical layers on devices which support more than one; never implemented. - *ifi\_addrlen* (*u\_char*) Length of a link-layer address on this device, or zero if there are none. Used to initialized the address length field in *sockaddr\_dl* structures referring to this interface. - *ifi\_hdrlen* (*u\_char*) Maximum length of any link-layer header which might be prepended by the driver to a packet before transmission. The generic code computes the maximum over all interfaces and uses that value to influence the placement of data in *mbuf*s to attempt to ensure that there is always sufficient space to prepend a link-layer header without allocating an additional *mbuf*. - *ifi\_datalen* (*u\_char*) Length of the *if\_data* structure. Allows some stabilization of the routing socket ABI in the face of increases in the length of *struct* *ifdata*. - *ifi\_mtu* (*u\_long*) The maximum transmission unit of the medium, exclusive of any link-layer overhead. - *ifi\_metric* (*u\_long*) A dimensionless metric interpreted by a user-mode routing process. - *ifi\_baudrate* (*u\_long*) The line rate of the interface, in bits per second. - *ifi\_hwassist* (*u\_long*) A detailed interpretation of the capabilities to offload computational tasks for *outgoing* packets. The interface driver must keep this field in accord with the current value of *if\_capenable*. - *ifi\_epoch* (*time\_t*) The system uptime when interface was attached or the statistics below were reset. This is intended to be used to set the SNMP variable *ifCounterDiscontinuityTime*. It may also be used to determine if two successive queries for an interface of the same index have returned results for the same interface. The structure additionally contains generic statistics applicable to a variety of different interface types (except as noted, all members are of type *u\_long*): - *ifi\_link\_state* (*u\_char*) The current link state of Ethernet interfaces. See the Interface Link States section for possible values. - *ifi\_ipackets* Number of packets received. - *ifi\_ierrors* Number of receive errors detected (e.g., FCS errors, DMA overruns, etc.). More detailed breakdowns can often be had by way of a link-specific MIB. - *ifi\_opackets* Number of packets transmitted. - *ifi\_oerrors* Number of output errors detected (e.g., late collisions, DMA overruns, etc.). More detailed breakdowns can often be had by way of a link-specific MIB. - *ifi\_collisions* Total number of collisions detected on output for CSMA interfaces. (This member is sometimes \[ab\]used by other types of interfaces for other output error counts.) - *ifi\_ibytes* Total traffic received, in bytes. - *ifi\_obytes* Total traffic transmitted, in bytes. - *ifi\_imcasts* Number of packets received which were sent by link-layer multicast. - *ifi\_omcasts* Number of packets sent by link-layer multicast. - *ifi\_iqdrops* Number of packets dropped on input. Rarely implemented. - *ifi\_noproto* Number of packets received for unknown network-layer protocol. - *ifi\_lastchange* (*struct timeval*) The time of the last administrative change to the interface (as required for SNMP). ### Interface Types The header file ⟨net/if\_types.h⟩ defines symbolic constants for a number of different types of interfaces. The most common are: - IFT\_OTHER none of the following - IFT\_ETHER Ethernet - IFT\_ISO88023 ISO 8802-3 CSMA/CD - IFT\_ISO88024 ISO 8802-4 Token Bus - IFT\_ISO88025 ISO 8802-5 Token Ring - IFT\_ISO88026 ISO 8802-6 DQDB MAN - IFT\_FDDI FDDI - IFT\_PPP Internet Point-to-Point Protocol ([ppp(8)](/ppp/8.md)) - IFT\_LOOP The loopback ([lo(4)](/lo/4.md)) interface - IFT\_SLIP Serial Line IP - IFT\_PARA Parallel-port IP (“PLIP”) - IFT\_ATM Asynchronous Transfer Mode ### Interface Link States The following link states are currently defined: - LINK\_STATE\_UNKNOWN The link is in an invalid or unknown state. - LINK\_STATE\_DOWN The link is down. - LINK\_STATE\_UP The link is up. ### The Vt ifaddr Ss Structure Every interface is associated with a list (or, rather, a TAILQ) of addresses, rooted at the interface structure's *if\_addrlist* member. The first element in this list is always an AF\_LINK address representing the interface itself; multi-access network drivers should complete this structure by filling in their link-layer addresses after calling **if\_attach**(). Other members of the structure represent network-layer addresses which have been configured by means of the SIOCAIFADDR command to [ioctl(2)](/ioctl/2.md), called on a socket of the appropriate protocol family. The elements of this list consist of *ifaddr* structures. Most protocols will declare their own protocol-specific interface address structures, but all begin with a *struct ifaddr* which provides the most-commonly-needed functionality across all protocols. Interface addresses are reference-counted. The members of *struct ifaddr* are as follows: - *ifa\_addr* (*struct sockaddr \**) The local address of the interface. - *ifa\_dstaddr* (*struct sockaddr \**) The remote address of point-to-point interfaces, and the broadcast address of broadcast interfaces. (*ifa\_broadaddr* is a macro for *ifa\_dstaddr*.) - *ifa\_netmask* (*struct sockaddr \**) The network mask for multi-access interfaces, and the confusion generator for point-to-point interfaces. - *ifa\_ifp* (*struct ifnet \**) A link back to the interface structure. - *ifa\_link* (**TAILQ\_ENTRY**(*ifaddr*)) [queue(3)](/queue/3.md) glue for list of addresses on each interface. - *ifa\_rtrequest* See below. - *ifa\_flags* (*u\_short*) Some of the flags which would be used for a route representing this address in the route table. - *ifa\_refcnt* (*short*) The reference count. - *ifa\_metric* (*int*) A metric associated with this interface address, for the use of some external routing protocol. References to *ifaddr* structures are gained manually, by incrementing the *ifa\_refcnt* member. References are released by calling either the **ifafree**() function or the **IFAFREE**() macro. **ifa\_rtrequest**() is a pointer to a function which receives callouts from the routing code (**rtrequest**()) to perform link-layer-specific actions upon requests to add, resolve, or delete routes. The *cmd* argument indicates the request in question: RTM\_ADD, RTM\_RESOLVE, or RTM\_DELETE. The *rt* argument is the route in question; the *dst* argument is the specific destination being manipulated for RTM\_RESOLVE, or a null pointer otherwise. ## FUNCTIONS The functions provided by the generic interface code can be divided into two groups: those which manipulate interfaces, and those which manipulate interface addresses. In addition to these functions, there may also be link-layer support routines which are used by a number of drivers implementing a specific link layer over different hardware; see the documentation for that link layer for more details. ### The Vt ifmultiaddr Ss Structure Every multicast-capable interface is associated with a list of multicast group memberships, which indicate at a low level which link-layer multicast addresses (if any) should be accepted, and at a high level, in which network-layer multicast groups a user process has expressed interest. The elements of the structure are as follows: - *ifma\_link* (**LIST\_ENTRY**(*ifmultiaddr*)) [queue(3)](/queue/3.md) macro glue. - *ifma\_addr* (*struct sockaddr \**) A pointer to the address which this record represents. The memberships for various address families are stored in arbitrary order. - *ifma\_lladdr* (*struct sockaddr \**) A pointer to the link-layer multicast address, if any, to which the network-layer multicast address in *ifma\_addr* is mapped, else a null pointer. If this element is non-nil, this membership also holds an invisible reference to another membership for that link-layer address. - *ifma\_refcount* (*u\_int*) A reference count of requests for this particular membership. ### Interface Manipulation Functions - **if\_alloc**() Allocate and initialize *struct ifnet*. Initialization includes the allocation of an interface index and may include the allocation of a *type* specific structure in *if\_l2com*. - **if\_attach**() Link the specified interface *ifp* into the list of network interfaces. Also initialize the list of addresses on that interface, and create a link-layer *ifaddr* structure to be the first element in that list. (A pointer to this address structure is saved in the global array *ifnet\_addrs*.) The *ifp* must have been allocted by **if\_alloc**(). - **if\_detach**() Shut down and unlink the specified *ifp* from the interface list. - **if\_free**() Free the given *ifp* back to the system. The interface must have been previously detached if it was ever attached. - **if\_free\_type**() Identical to **if\_free**() except that the given *type* is used to free *if\_l2com* instead of the type in *if\_type*. This is intended for use with drivers that change their interface type. - **if\_down**() Mark the interface *ifp* as down (i.e., IFF\_UP is not set), flush its output queue, notify protocols of the transition, and generate a message from the [route(4)](/route/4.md) routing socket. - **if\_up**() Mark the interface *ifp* as up, notify protocols of the transition, and generate a message from the [route(4)](/route/4.md) routing socket. - **ifpromisc**() Add or remove a promiscuous reference to *ifp*. If *pswitch* is true, add a reference; if it is false, remove a reference. On reference count transitions from zero to one and one to zero, set the IFF\_PROMISC flag appropriately and call **if\_ioctl**() to set up the interface in the desired mode. - **if\_allmulti**() As **ifpromisc**(), but for the all-multicasts (IFF\_ALLMULTI) flag instead of the promiscuous flag. - **ifunit**() Return an *ifnet* pointer for the interface named *name*. - **ifioctl**() Process the ioctl request *cmd*, issued on socket *so* by thread *td*, with data parameter *data*. This is the main routine for handling all interface configuration requests from user mode. It is ordinarily only called from the socket-layer [ioctl(2)](/ioctl/2.md) handler, and only for commands with class ‘i’. Any unrecognized commands will be passed down to socket *so*'s protocol for further interpretation. The following commands are handled by **ifioctl**(): - SIOCGIFCONF - OSIOCGIFCONF Get interface configuration. (No call-down to driver.) - SIOCSIFNAME Set the interface name. RTM\_IFANNOUNCE departure and arrival messages are sent so that routing code that relies on the interface name will update its interface list. Caller must have appropriate privilege. (No call-down to driver.) - SIOCGIFCAP - SIOCGIFFLAGS - SIOCGIFMETRIC - SIOCGIFMTU - SIOCGIFPHYS Get interface capabilities, flags, metric, MTU, medium selection. (No call-down to driver.) - SIOCSIFCAP Enable or disable interface capabilities. Caller must have appropriate privilege. Before a call to the driver-specific **if\_ioctl**() routine, the requested mask for enabled capabilities is checked against the mask of capabilities supported by the interface, *if\_capabilities*. Requesting to enable an unsupported capability is invalid. The rest is supposed to be done by the driver, which includes updating *if\_capenable* and *if\_data.ifi\_hwassist* appropriately. - SIOCSIFFLAGS Change interface flags. Caller must have appropriate privilege. If a change to the IFF\_UP flag is requested, **if\_up**() or **if\_down**() is called as appropriate. Flags listed in IFF\_CANTCHANGE are masked off, and the field *if\_flags* in the interface structure is updated. Finally, the driver **if\_ioctl**() routine is called to perform any setup requested. - SIOCSIFMETRIC - SIOCSIFPHYS Change interface metric or medium. Caller must have appropriate privilege. - SIOCSIFMTU Change interface MTU. Caller must have appropriate privilege. MTU values less than 72 or greater than 65535 are considered invalid. The driver **if\_ioctl**() routine is called to implement the change; it is responsible for any additional sanity checking and for actually modifying the MTU in the interface structure. - SIOCADDMULTI - SIOCDELMULTI Add or delete permanent multicast group memberships on the interface. Caller must have appropriate privilege. The **if\_addmulti**() or **if\_delmulti**() function is called to perform the operation; qq.v. - SIOCSIFDSTADDR - SIOCSIFADDR - SIOCSIFBRDADDR - SIOCSIFNETMASK The socket's protocol control routine is called to implement the requested action. - OSIOGIFADDR - OSIOCGIFDSTADDR - OSIOCGIFBRDADDR - OSIOCGIFNETMASK The socket's protocol control routine is called to implement the requested action. On return, *sockaddr* structures are converted into old-style (no *sa\_len* member). **if\_down**(), **ifioctl**(), **ifpromisc**(), and **if\_up**() must be called at **splnet**() or higher. ### Interface Address Functions Several functions exist to look up an interface address structure given an address. **ifa\_ifwithaddr**() returns an interface address with either a local address or a broadcast address precisely matching the parameter *addr*. **ifa\_ifwithdstaddr**() returns an interface address for a point-to-point interface whose remote (“destination”) address is *addr*. **ifa\_ifwithnet**() returns the most specific interface address which matches the specified address, *addr*, subject to its configured netmask, or a point-to-point interface address whose remote address is *addr* if one is found. **ifaof\_ifpforaddr**() returns the most specific address configured on interface *ifp* which matches address *addr*, subject to its configured netmask. If the interface is point-to-point, only an interface address whose remote address is precisely *addr* will be returned. All of these functions return a null pointer if no such address can be found. ### Interface Multicast Address Functions The **if\_addmulti**(), **if\_delmulti**(), and **ifmaof\_ifpforaddr**() functions provide support for requesting and relinquishing multicast group memberships, and for querying an interface's membership list, respectively. The **if\_addmulti**() function takes a pointer to an interface, *ifp*, and a generic address, *sa*. It also takes a pointer to a *struct ifmultiaddr \** which is filled in on successful return with the address of the group membership control block. The **if\_addmulti**() function performs the following four-step process: 1. Call the interface's **if\_resolvemulti**() entry point to determine the link-layer address, if any, corresponding to this membership request, and also to give the link layer an opportunity to veto this membership request should it so desire. 2. Check the interface's group membership list for a pre-existing membership for this group. If one is not found, allocate a new one; if one is, increment its reference count. 3. If the **if\_resolvemulti**() routine returned a link-layer address corresponding to the group, repeat the previous step for that address as well. 4. If the interface's multicast address filter needs to be changed because a new membership was added, call the interface's **if\_ioctl**() routine (with a *cmd* argument of SIOCADDMULTI) to request that it do so. The **if\_delmulti**() function, given an interface *ifp* and an address, *sa*, reverses this process. Both functions return zero on success, or a standard error number on failure. The **ifmaof\_ifpforaddr**() function examines the membership list of interface *ifp* for an address matching *addr*, and returns a pointer to that *struct ifmultiaddr* if one is found, else it returns a null pointer. ## SEE ALSO [ioctl(2)](/ioctl/2.md), [link\_addr(3)](/link_addr/3.md), [queue(3)](/queue/3.md), [sysctl(3)](/sysctl/3.md), [bpf(4)](/bpf/4.md), [ifmib(4)](/ifmib/4.md), [lo(4)](/lo/4.md), [netintro(4)](/netintro/4.md), [polling(4)](/polling/4.md), [config(8)](/config/8.md), [ppp(8)](/ppp/8.md), [mbuf(9)](/mbuf/9.md), [rtentry(9)](/rtentry/9.md) Gary R. Wright and W. Richard Stevens, *TCP/IP Illustrated*, Vol. 2, Addison-Wesley, ISBN 0-201-63354-X. ## AUTHORS This manual page was written by Garrett A. Wollman.