NPF(3)

NAME
npf - NPF packet filter library

LIBRARY
libnpf

SYNOPSIS
#include <npf.h>
nl_config_t *
npf_config_create(void);
int
npf_config_submit(nl_config_t *ncf, int fd);
void
npf_config_destroy(nl_config_t *ncf);
nl_rule_t *
npf_rule_create(char *name, uint32_t attr, u_int if_idx);
int
npf_rule_setcode(nl_rule_t *rl, int type, const void *code, size_t sz);
bool
npf_rule_exists_p(nl_config_t *ncf, const char *name);
int
npf_rule_insert(nl_config_t *ncf, nl_rule_t *parent, nl_rule_t *rl, pri_t pri);
int
npf_rule_setproc(nl_config_t *ncf, nl_rule_t *rl, const char *name);
void
npf_rule_destroy(nl_rule_t *rl);
nl_rproc_t *
npf_rproc_create(char *name);
bool
npf_rproc_exists_p(nl_config_t *ncf, const char *name);
int
npf_rproc_insert(nl_config_t *ncf, nl_rproc_t *rp);
nl_nat_t *
npf_nat_create(int type, int flags, u_int if_idx, npf_addr_t *addr, int af, in_port_t port);
int
npf_nat_insert(nl_config_t *ncf, nl_nat_t *nt, pri_t pri);
nl_table_t *
npf_table_create(int index, int type);
int
npf_table_add_entry(nl_table_t *tl, in_addr_t addr, in_addr_t mask);
bool
npf_table_exists_p(nl_config_t *ncf, u_int tid);
int
npf_table_insert(nl_config_t *ncf, nl_table_t *tl);
void
npf_table_destroy(nl_table_t *tl);
int
npf_update_rule(int fd, char *rname, nl_rule_t *rl);
int
npf_sessions_send(int fd, const char *fpath);
int
npf_sessions_recv(int fd, const char *fpath);

DESCRIPTION
The npf library provides an interface to create an NPF configuration having rules, tables, procedures, or translation policies. The configuration can be submitted to the kernel.

FUNCTIONS

  Configuration

npf_config_create()
    Create a configuration.

npf_config_submit(ncf, fd)
    Submit configuration ncf to the kernel.

npf_config_destroy(ncf)
    Destroy the configuration ncf.

  Rule interface

npf_rule_create(name, attr, if_idx)
    Create a rule with a given name, attribute and priorty. Name can be NULL, in which case rule has no unique identifier. Otherwise, rules shall not have duplicate names. The following attributes, which can be ORed, are available:

    NPF_RULE_PASS
        Decision of this rule is "pass". If this attribute is not specified, then packet "block" (drop) is the default.

    NPF_RULE_DEFAULT
        This a default rule in the ruleset. There can only be a single rule having this attribute set in the ruleset.

    NPF_RULE_FINAL
        Indicates that on rule match, further processing of the ruleset should be stopped and this rule applied instantly.

    NPF_RULE_KEEPSTATE
        Create a state (session) on match, track the connection and therefore pass the backwards stream without inspection.

    NPF_RULE_RETRST
        Return TCP RST packet in a case of packet block.

    NPF_RULE_RETICMP
        Return ICMP destination unreachable in a case of packet block.

    NPF_RULE_IN
        Rule may match only if incoming packet.

    NPF_RULE_OUT
        Rule may match only if outgoing packet.

    Interface is specified by if_idx, which is a numeral representation of an interface, given by if_nametoindex(3). Zero indicates any interface.

npf_rule_setcode(rl, type, code, sz)
    Assign compiled code for the rule specified by rl, used for filter criteria. Pointer to the binary code is specified by code, and size of the memory area by sz. Type of the code is specified by type. Currently, only n-code is supported and NPF_CODE_NCODE should be passed.

npf_rule_insert(ncf, parent, rl, pri)
    Insert the rule into the set of parent rule specified by parent. If value of parent is NULL, then insert into the main ruleset.

    Priority is the order of the rule in the ruleset. Lower value means first to process, higher value - last to process. If multiple rules have the same priority - order is unspecified. A special constant NPF_PRI_NEXT may be passed to use the value of last used priority incremented by 1.

npf_rule_setproc(ncf, rl, name)
    Set procedure for the specified rule.

npf_rule_destroy(rl)
    Destroy the given rule.

  Rule procedure interface

npf_rproc_create(name)
    Create a rule procedure with a given name. Name must be unique for each procedure.

npf_rproc_insert(ncf, rp)
    Insert rule procedure into the specified configuration.

  Translation interface

npf_nat_create(type, flags, if_idx, addr, af, port)
    Create a NAT translation policy of a specified type. There are two types:

    NPF_NATIN
        Inbound NAT policy.

    NPF_NATOUT
        Outbound NAT policy.

    A bi-directional NAT is obtained by combining two policies. The following flags are supported:

    NPF_NAT_PORTS
        Indicates to perform port translation. Otherwise, port translation is not performed and port is ignored.

    NPF_NAT_PORTMAP
        Effective only if NPF_NAT_PORTS flag is set. Indicates to create a port map and select a random port for translation. Otherwise, port is translated to the value specified by port is used.

    Translation address is specified by addr, and its family by fa. Family must be either AF_INET for IPv4 or AF_INET6 for IPv6 address.

npf_nat_insert(ncf, nt, pri)
    Insert NAT policy, its rule, into the specified configuration.

  Table interface

npf_table_create(index, type)
    Create NPF table of specified type. The following types are supported:

    NPF_TABLE_HASH
        Indicates to use hash table for storage.

    NPF_TABLE_RBTREE
        Indicates to use red-black tree for storage. Table is identified by index, which should be in the range between 1 and NPF_MAX_TABLE_ID.

npf_table_add_entry(tl, addr, mask)
    Add an entry of IPv4 address and mask, specified by addr and mask, to the table specified by tl.

npf_table_exists_p(ncf, name)
    Determine whether table with ID tid exists in the configuration ncf. Return true if exists, and false otherwise.

npf_table_insert(ncf, tl)
    Insert table into set of configuration. Routine performs a check for duplicate table ID.

npf_table_destroy(tl)
    Destroy the specified table.

  Session interface

npf_update_rule(fd, rname, rl)

npf_sessions_send(fd, fpath)
    Read the file specified by fpath, and send sessions saved in it to the kernel.

npf_sessions_recv(fd, fpath)
    Receive currently loaded session from the kernel, and save them to a file specified by fpath.

SEE ALSO
npfctl(8), npf_ncode(9)

HISTORY
The NPF library first appeared in NetBSD 6.0.