490 lines
13 KiB
Groff
490 lines
13 KiB
Groff
.\"
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.\" Copyright (c) 2010 The FreeBSD Foundation
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.\" All rights reserved.
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.\"
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.\" Portions of this documentation were written by Shteryana Sotirova Shopova
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.\" under sponsorship from the FreeBSD Foundation.
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.\"
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.\" Copyright (c) 2004-2005
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.\" Hartmut Brandt.
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.\" All rights reserved.
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.\" Copyright (c) 2001-2003
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.\" Fraunhofer Institute for Open Communication Systems (FhG Fokus).
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.\" All rights reserved.
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.\"
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.\" Author: Harti Brandt <harti@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $Begemot: bsnmp/lib/bsnmplib.3,v 1.9 2005/10/04 08:46:51 brandt_h Exp $
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.\"
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.Dd September 9, 2010
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.Dt BSNMPLIB 3
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.Os
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.Sh NAME
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.Nm snmp_value_free ,
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.Nm snmp_value_parse ,
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.Nm snmp_value_copy ,
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.Nm snmp_pdu_free ,
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.Nm snmp_pdu_decode ,
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.Nm snmp_pdu_encode ,
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.Nm snmp_pdu_decode_header ,
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.Nm snmp_pdu_decode_scoped ,
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.Nm snmp_pdu_decode_secmode ,
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.Nm snmp_pdu_dump ,
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.Nm snmp_passwd_to_keys ,
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.Nm snmp_get_local_keys ,
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.Nm snmp_calc_keychange ,
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.Nm TRUTH_MK ,
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.Nm TRUTH_GET ,
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.Nm TRUTH_OK
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.Nd "SNMP decoding and encoding library"
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.Sh LIBRARY
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Begemot SNMP library
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.Pq libbsnmp, -lbsnmp
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.Sh SYNOPSIS
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.In bsnmp/asn1.h
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.In bsnmp/snmp.h
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.Ft void
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.Fn snmp_value_free "struct snmp_value *value"
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.Ft int
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.Fn snmp_value_parse "const char *buf" "enum snmp_syntax" "union snmp_values *value"
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.Ft int
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.Fn snmp_value_copy "struct snmp_value *to" "const struct snmp_value *from"
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.Ft void
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.Fn snmp_pdu_free "struct snmp_pdu *value"
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.Ft enum snmp_code
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.Fn snmp_pdu_decode "struct asn_buf *buf" "struct snmp_pdu *pdu" "int32_t *ip"
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.Ft enum snmp_code
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.Fn snmp_pdu_encode "struct snmp_pdu *pdu" "struct asn_buf *buf"
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.Ft enum snmp_code
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.Fn snmp_pdu_decode_header "struct snmp_pdu *pdu" "struct asn_buf *buf"
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.Ft enum snmp_code
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.Fn snmp_pdu_decode_scoped "struct asn_buf *buf" "struct snmp_pdu *pdu" "int32_t *ip"
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.Ft enum snmp_code
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.Fn snmp_pdu_decode_secmode "struct asn_buf *buf" "struct snmp_pdu *pdu"
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.Ft void
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.Fn snmp_pdu_dump "const struct snmp_pdu *pdu"
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.Ft enum snmp_code
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.Fn snmp_passwd_to_keys "struct snmp_user *user" "char *passwd"
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.Ft enum snmp_code
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.Fn snmp_get_local_keys "struct snmp_user *user" "uint8_t *eid" "uint32_t elen"
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.Ft enum snmp_code
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.Fn snmp_calc_keychange "struct snmp_user *user" "uint8_t *keychange"
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.Ft int
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.Fn TRUTH_MK "F"
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.Ft int
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.Fn TRUTH_GET "T"
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.Ft int
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.Fn TRUTH_OK "T"
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.Sh DESCRIPTION
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The SNMP library contains routines to handle SNMP version 1, 2 and 3 PDUs.
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There are several basic structures used throughout the library:
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.Bd -literal -offset indent
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struct snmp_value {
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struct asn_oid var;
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enum snmp_syntax syntax;
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union snmp_values {
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int32_t integer;/* also integer32 */
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struct {
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u_int len;
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u_char *octets;
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} octetstring;
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struct asn_oid oid;
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u_char ipaddress[4];
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uint32_t uint32; /* also gauge32, counter32,
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unsigned32, timeticks */
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uint64_t counter64;
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} v;
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};
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.Ed
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.Pp
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This structure represents one variable binding from an SNMP PDU.
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The field
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.Fa var
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is the ASN.1 of the variable that is bound.
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.Fa syntax
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contains either the syntax code of the value or an exception code for SNMPv2
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and may be one of:
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.Bd -literal -offset indent
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enum snmp_syntax {
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SNMP_SYNTAX_NULL = 0,
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SNMP_SYNTAX_INTEGER, /* == INTEGER32 */
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SNMP_SYNTAX_OCTETSTRING,
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SNMP_SYNTAX_OID,
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SNMP_SYNTAX_IPADDRESS,
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SNMP_SYNTAX_COUNTER,
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SNMP_SYNTAX_GAUGE, /* == UNSIGNED32 */
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SNMP_SYNTAX_TIMETICKS,
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/* v2 additions */
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SNMP_SYNTAX_COUNTER64,
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/* exceptions */
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SNMP_SYNTAX_NOSUCHOBJECT,
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SNMP_SYNTAX_NOSUCHINSTANCE,
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SNMP_SYNTAX_ENDOFMIBVIEW,
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};
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.Ed
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The field
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.Fa v
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holds the actual value depending on
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.Fa syntax .
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Note, that if
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.Fa syntax
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is
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.Li SNMP_SYNTAX_OCTETSTRING
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and
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.Fa v.octetstring.len
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is not zero,
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.Fa v.octetstring.octets
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points to a string allocated by
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.Xr malloc 3 .
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.Pp
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.Bd -literal -offset indent
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#define SNMP_ENGINE_ID_SIZ 32
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struct snmp_engine {
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uint8_t engine_id[SNMP_ENGINE_ID_SIZ];
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uint32_t engine_len;
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int32_t engine_boots;
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int32_t engine_time;
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int32_t max_msg_size;
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};
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.Ed
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.Pp
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This structure represents an SNMP engine as specified by the SNMP Management
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Architecture described in RFC 3411.
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.Pp
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.Bd -literal -offset indent
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#define SNMP_USM_NAME_SIZ (32 + 1)
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#define SNMP_AUTH_KEY_SIZ 40
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#define SNMP_PRIV_KEY_SIZ 32
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struct snmp_user {
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char sec_name[SNMP_USM_NAME_SIZ];
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enum snmp_authentication auth_proto;
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enum snmp_privacy priv_proto;
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uint8_t auth_key[SNMP_AUTH_KEY_SIZ];
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uint8_t priv_key[SNMP_PRIV_KEY_SIZ];
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};
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.Ed
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.Pp
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This structure represents an SNMPv3 user as specified by the User-based
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Security Model (USM) described in RFC 3414. The field
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.Fa sec_name
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is a human readable string containing the security user name.
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.Fa auth_proto
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contains the id of the authentication protocol in use by the user and may be one
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of:
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.Bd -literal -offset indent
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enum snmp_authentication {
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SNMP_AUTH_NOAUTH = 0,
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SNMP_AUTH_HMAC_MD5,
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SNMP_AUTH_HMAC_SHA
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};
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.Ed
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.Fa priv_proto
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contains the id of the privacy protocol in use by the user and may be one
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of:
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.Bd -literal -offset indent
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enum snmp_privacy {
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SNMP_PRIV_NOPRIV = 0,
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SNMP_PRIV_DES = 1,
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SNMP_PRIV_AES
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};
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.Ed
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.Fa auth_key
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and
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.Fa priv_key
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contain the authentication and privacy keys for the user.
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.Pp
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.Bd -literal -offset indent
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#define SNMP_COMMUNITY_MAXLEN 128
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#define SNMP_MAX_BINDINGS 100
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#define SNMP_CONTEXT_NAME_SIZ (32 + 1)
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#define SNMP_TIME_WINDOW 150
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#define SNMP_USM_AUTH_SIZE 12
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#define SNMP_USM_PRIV_SIZE 8
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#define SNMP_MSG_AUTH_FLAG 0x1
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#define SNMP_MSG_PRIV_FLAG 0x2
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#define SNMP_MSG_REPORT_FLAG 0x4
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#define SNMP_SECMODEL_USM 3
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struct snmp_pdu {
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char community[SNMP_COMMUNITY_MAXLEN + 1];
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enum snmp_version version;
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u_int type;
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/* SNMPv3 PDU header fields */
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int32_t identifier;
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uint8_t flags;
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int32_t security_model;
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struct snmp_engine engine;
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/* Associated USM user parameters */
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struct snmp_user user;
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uint8_t msg_digest[SNMP_USM_AUTH_SIZE];
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uint8_t msg_salt[SNMP_USM_PRIV_SIZE];
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/* View-based Access Model */
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uint32_t context_engine_len;
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uint8_t context_engine[SNMP_ENGINE_ID_SIZ];
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char context_name[SNMP_CONTEXT_NAME_SIZ];
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/* trap only */
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struct asn_oid enterprise;
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u_char agent_addr[4];
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int32_t generic_trap;
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int32_t specific_trap;
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uint32_t time_stamp;
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/* others */
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int32_t request_id;
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int32_t error_status;
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int32_t error_index;
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/* fixes for encoding */
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size_t outer_len;
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size_t scoped_len;
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u_char *outer_ptr;
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u_char *digest_ptr;
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u_char *encrypted_ptr;
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u_char *scoped_ptr;
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u_char *pdu_ptr;
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u_char *vars_ptr;
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struct snmp_value bindings[SNMP_MAX_BINDINGS];
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u_int nbindings;
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};
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.Ed
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This structure contains a decoded SNMP PDU.
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.Fa version
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is one of
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.Bd -literal -offset indent
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enum snmp_version {
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SNMP_Verr = 0,
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SNMP_V1 = 1,
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SNMP_V2c,
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SNMP_V3
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};
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.Ed
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and
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.Fa type
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is the type of the PDU.
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.Fa security_model
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is the security model used for SNMPv3 PDUs. The only supported
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value currently is 3 (User-based Security Model).
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.Pp
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The function
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.Fn snmp_value_free
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is used to free all the dynamic allocated contents of an SNMP value.
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It does not free the structure pointed to by
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.Fa value
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itself.
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.Pp
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The function
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.Fn snmp_value_parse
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parses the ASCII representation of an SNMP value into its binary form.
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This function is mainly used by the configuration file reader of
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.Xr bsnmpd 1 .
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.Pp
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The function
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.Fn snmp_value_copy
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makes a deep copy of the value pointed to by
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.Fa from
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to the structure pointed to by
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.Fa to .
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It assumes that
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.Fa to
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is uninitialized and will overwrite its previous contents.
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It does not itself allocate the structure pointed to by
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.Fa to .
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.Pp
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The function
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.Fn snmp_pdu_free
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frees all the dynamically allocated components of the PDU.
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It does not itself free the structure pointed to by
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.Fa pdu .
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.Pp
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The function
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.Fn snmp_pdu_decode
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decodes the PDU pointed to by
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.Fa buf
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and stores the result into
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.Fa pdu .
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If an error occurs in a variable binding the (1 based) index of this binding
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is stored in the variable pointed to by
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.Fa ip .
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.Pp
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The function
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.Fn snmp_pdu_encode
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encodes the PDU
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.Fa pdu
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into the an octetstring in buffer, and if authentication and privacy are used,
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calculates a message digest and encrypts the PDU data in the buffer
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.Fa buf .
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.Pp
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The function
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.Fn snmp_pdu_decode_header
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decodes the header of the PDU pointed to by
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.Fa buf .
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The uncoded PDU contents remain in the buffer.
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.Pp
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The function
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.Fn snmp_pdu_decode_scoped
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decodes the scoped PDU pointed to by
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.Fa buf .
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.Pp
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The function
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.Fn snmp_pdu_decode_secmode
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verifies the authentication parameter contained in the PDU (if present) and
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if the PDU is encrypted, decrypts the PDU contents pointed to by
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.Fa buf .
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If successfull, a plain text scoped PDU is stored in the buffer.
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.Pp
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The function
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.Fn snmp_pdu_dump
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dumps the PDU in a human readable form by calling
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.Fn snmp_printf .
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.Pp
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The function
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.Fn snmp_passwd_to_keys
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calculates a binary private authentication key corresponding to a plain text human
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readable password string. The calculated key is placed in the
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.Fa auth_key
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field of the
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.Fa user .
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.Pp
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The function
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.Fn snmp_get_local_keys
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calculates a localazied authentication and privacy keys for a specified SNMPv3
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engine. The calculateds keys are placed in the
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.Fa auth_key
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and
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.Fa priv_key
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fields of the
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.Fa user .
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.Pp
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The function
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.Fn snmp_calc_keychange
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calculates a binary key change octet string based on the contents of an old and
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a new binary localized key. The rezult is placed in the buffer pointer to by
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.Fa keychange
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and may be used by an SNMPv3 user who wishes to change his/her password
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or localized key.
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.Pp
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The function
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.Fn TRUTH_MK
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takes a C truth value (zero or non-zero) and makes an SNMP truth value (2 or 1).
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The function
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.Fn TRUTH_GET
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takes an SNMP truth value and makes a C truth value (0 or 1).
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The function
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.Fn TRUTH_OK
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checks, whether its argument is a legal SNMP truth value.
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.Sh DIAGNOSTICS
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When an error occurs in any of the function the function pointed to
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by the global pointer
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.Bd -literal -offset indent
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extern void (*snmp_error)(const char *, ...);
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.Ed
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.Pp
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with a
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.Xr printf 3
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style format string.
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There is a default error handler in the library that prints a message
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starting with
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.Sq SNMP:
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followed by the error message to standard error.
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.Pp
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The function pointed to by
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.Bd -literal -offset indent
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extern void (*snmp_printf)(const char *, ...);
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.Ed
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.Pp
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is called by the
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.Fn snmp_pdu_dump
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function.
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The default handler is
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.Xr printf 3 .
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.Sh ERRORS
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.Fn snmp_pdu_decode
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will return one of the following return codes:
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.Bl -tag -width Er
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.It Bq Er SNMP_CODE_OK
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Success.
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.It Bq Er SNMP_CODE_FAILED
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The ASN.1 coding was wrong.
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.It Bq Er SNMP_CODE_BADLEN
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A variable binding value had a wrong length field.
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.It Bq Er SNMP_CODE_OORANGE
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A variable binding value was out of the allowed range.
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.It Bq Er SNMP_CODE_BADVERS
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The PDU is of an unsupported version.
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.It Bq Er SNMP_CODE_BADENQ
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There was an ASN.1 value with an unsupported tag.
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.It Bq Er SNMP_CODE_BADSECLEVEL
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The requested securityLevel contained in the PDU is not supported.
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.It Bq Er SNMP_CODE_BADDIGEST
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The PDU authentication parameter received in the PDU did not match the
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calculated message digest.
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.It Bq Er SNMP_CODE_EDECRYPT
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Error occured while trying to decrypt the PDU.
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.El
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.Pp
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.Fn snmp_pdu_encode
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will return one of the following return codes:
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.Bl -tag -width Er
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.It Bq Er SNMP_CODE_OK
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Success.
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.It Bq Er SNMP_CODE_FAILED
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Encoding failed.
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.El
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.Sh SEE ALSO
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.Xr gensnmptree 1 ,
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.Xr bsnmpd 1 ,
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.Xr bsnmpagent 3 ,
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.Xr bsnmpclient 3 ,
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.Xr bsnmplib 3
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.Sh CAVEAT
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The SNMPv3 message digests, encryption and decryption, and key routines use
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the cryptographic functions from
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.Xr crypto 3 .
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The library may optionally be built without references to the
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.Xr crypto 3
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library. In such case only plain text SNMPv3 PDUs without message digests
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may be proccessed correctly.
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.Sh STANDARDS
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This implementation conforms to the applicable IETF RFCs and ITU-T
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recommendations.
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.Sh AUTHORS
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The Begemot SNMP library was originally written by
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.An Hartmut Brandt Aq harti@FreeBSD.org
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.Pp
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.An Shteryana Shopova Aq syrinx@FreeBSD.org
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added support for the SNMPv3 message proccessing and User-Based
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Security model message authentication and privacy.
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