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准备工作

CentOS7

，

net-snmp-5.7.2


1.

snmp

安装及配置

安装snmp

• net-snmp: snmp服务端
• net-snmp-utils：snmp客户端工具集
• net-snmp-perl：snmp mib库编译工具

yum install -y net-snmp net-snmp-utils net-snmp-perl

配置snmp

...

#com2sec notConfigUser  default       public
# 配置允许访问agent的地址
com2sec notConfigUser  192.168.51.0/24      public
# 这两行注释
#view systemview included .1.3.6.1.2.1.1
#view systemview included .1.3.6.1.2.1.25.1.1

# 新增，表示可以查看所有的信息
view all included .1
view systemview included .1
# 修改read为all
access notConfigGroup "" any noauth exact all none none
...

启动并验证snmp

# 192.168.52.104
systemctl start snmpd
systemctl enable snmpd

# snmpwalk -v 2c -c public 192.168.51.104 sysName.0
SNMPv2-MIB::sysName.0 = STRING: work1

2.

mib

编写及加载

自定义mib

# TEST-MIB.txt
-- TEST-MIB.txt
     TEST-MIB DEFINITIONS ::= BEGIN

         IMPORTS
             OBJECT-GROUP, MODULE-COMPLIANCE, NOTIFICATION-GROUP
                 FROM SNMPv2-CONF
             enterprises, Integer32, Unsigned32, OBJECT-TYPE, MODULE-IDENTITY,
             NOTIFICATION-TYPE
                 FROM SNMPv2-SMI
             DisplayString
                 FROM SNMPv2-TC;

         Test MODULE-IDENTITY
             LAST-UPDATED "202204061450Z"       --必须以Z结尾
             ORGANIZATION
                 ""
             CONTACT-INFO
                 ""
             DESCRIPTION
                 "Video's Server MIB."
             ::= { enterprises 30000 }

         Time OBJECT IDENTIFIER ::= { Test 1 }


         GetTime OBJECT-TYPE
             SYNTAX DisplayString
             MAX-ACCESS read-only
             STATUS current
             DESCRIPTION
                 "Example : 2022/4/6"
            ::= { Time 1 }
    END
-- TEST-MIB.txt

移动TEST-MIB.txt到SNMP mibs

mv TEST-MIB.txt usr/share/snmp/mibs/

新建目录并将mib文件转化为c文件

mkdir mib_test
cd mib_test
env MIBS="+/usr/share/snmp/mibs/TEST-MIB.txt" mib2c Test
#执行完成会生成 Test.h Test.c

编译自定义mib

补全Test.c

/*
 * Note: this file originally auto-generated by mib2c using
 *        $
 */

#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>
#include "Test.h"

/** Initializes the Test module */
void
init_Test(void)
{
    const oid GetTime_oid[] = { 1,3,6,1,4,1,30000,1,1 };

  DEBUGMSGTL(("Test", "Initializing\n"));

    netsnmp_register_scalar(
        netsnmp_create_handler_registration("GetTime", handle_GetTime,
                               GetTime_oid, OID_LENGTH(GetTime_oid),
                               HANDLER_CAN_RONLY
        ));
}

int
handle_GetTime(netsnmp_mib_handler *handler,
                          netsnmp_handler_registration *reginfo,
                          netsnmp_agent_request_info   *reqinfo,
                          netsnmp_request_info         *requests)
{
    /* We are never called for a GETNEXT if it's registered as a
       "instance", as it's "magically" handled for us.  */

    /* a instance handler also only hands us one request at a time, so
       we don't need to loop over a list of requests; we'll only get one. */
    time_t t;
    switch(reqinfo->mode) {
        case MODE_GET:
            time(&t);
            char szTime[100];
            snprintf(szTime,100,"%s",ctime(&t));
            snmp_set_var_typed_value(requests->requestvb, ASN_OCTET_STR,
                                     /* XXX: a pointer to the scalar's data */
                                     szTime,
                                     /* XXX: the length of the data in bytes */
                                     strlen(szTime));
            break;


        default:
            /* we should never get here, so this is a really bad error */
            snmp_log(LOG_ERR, "unknown mode (%d) in handle_GetTime\n", reqinfo->mode );
            return SNMP_ERR_GENERR;
    }

    return SNMP_ERR_NOERROR;
}

编写makefile

CC=gcc
FLAGS=-I. `net-snmp-config --cflags` -g
DLFLAGS=-shared -fPIC -g

Test.so: Test.c
        $(CC) $(CFLAGS) $(DLFLAGS) -c -o Test.o Test.c
        $(CC) $(CFLAGS) $(DLFLAGS) -o Test.so Test.o

.PHONY : clean
clean :
        rm -f *.so *.o

执行编译

make makefile
# 执行完毕会生成Test.so

配置snmp加载Test.so

# 配置snmp /etc/snmp/snmpd.conf

# 最后添加
dlmod Test /root/aa/Test.so

重新启动snmp

systemctl restart snmpd
systemctl status snmpd #查看snmpd是否正常启动

3.验证自定义的

mib

是否生效

snmpwalk -v 2c -c public localhost  .1.3.6.1.4.1.30000.1.1
SNMPv2-SMI::enterprises.30000.1.1.0 = STRING: "Wed Apr  6 10:20:53 2022
"

4.

mib

的添加方式

常见的snmp添加自定义mib库的方式有以下3种

静态加载

将生成的.c和.h文件加入到相应的位置，重新编译snmp库，优点是不需要修改配置文件，缺点是每次添加都得重新编译，方式如下。

# 把Test.c和Test.h复制到net-snmp源码中 net-snmp-5.7.2/agent/mibgroup，然后编译安装

./configure --prefix=/usr/local/snmp --with-mib-modules=Test，make && make install

动态加载

将生成的.c和.h文件再编译成.so库，修改snmpd.conf配置文件，优点是每次添加不需要重新编译，缺点是必须支持dlmod命令。

子代理扩展

将生成的.c和.h文件编译成可执行程序，运行该程序和snmpd即可，优点是操作简单，缺点是需要运行两个程序才行，方式如下。

# 生成Test程序：
net-snmp-config --compile-subagent Test Test.c
# 启动snmpd,Test
systemctl start snmpd
./Test