Configuring eCos

To use the SNMP agent, the SNMP library and agent packages must be included in your configuration. To incorporate the stack into your configuration select the SNMP library and SNMP agent packages in the eCos Configuration Tool, or at the command line type:

$ ecosconfig add snmplib snmpagent

After adding the networking, common ethernet device drivers, snmp library and snmp agent packages, there is no configuration required. However there are a number of configuration options that can be set such as some details for the System MIB, and disabling SNMPv3 support (see below).

Starting the SNMP agent is not integrated into network tests other than snmpping below, nor is it started automatically in normal eCos startup - it is up to the application to start the agent when it is ready, at least after the network interfaces are both ‘up’.

Version usage (v1, v2 or v3)

The default build supports all three versions of the SNMP protocol, but without any dispatcher functionality (rfc 2571, section 3.1.1.2). This has the following implications :

1. There is no community authentication for v1 and v2c.

2. Security provided by v3 can be bypassed by using v1/v2c protocol.

To provide the dispatcher with rfc 2571 type functionality, it is required to set up security models and access profiles. This can be provided in the normal Unix style by writing the required configurations in snmpd.conf file. Application code may setup profiles in snmpd.conf and optionally set the environment variable SNMPCONFPATH to point to the file if it is not in the usual location. The whole concept works in the usual way as with the standard UCD-SNMP distribution.

Traps

The support of the trapsink command in the snmpd.conf file is not tested and there may be problems for it working as expected. Moreover, in systems that do not have filesystem support, there is no way to configure a trap-session in the conventional way.

For reasons mentioned above, applications need to initialize their own trap sessions and pass it the details of trap-sink. The following is a small sample for initializing a v1 trap session :

typedef struct trap {
        unsigned char ip [4];
        unsigned int  port;
        unsigned char community [256];
}

trap            trapsink;
unsinged char   sink [16]; 

...
...

if (trapsink.ip != 0) {
        sprintf (sink, "%d.%d.%d.%d",
                 trapsink[0], trapsink[1], trapsink[2], trapsink[3]);
        if (create_trap_session (sink,
                trapsink.port,
                (char *)trapsink.community,
                SNMP_VERSION_1,
                SNMP_MSG_TRAP) == 0) {
                log_error ("Creation of trap session failed \n");
        }
}

snmpd.conf file

Using snmpd.conf requires the inclusion of one of the file-system packages (eg. CYGPKG_RAMFS) and CYGPKG_FILEIO. With these two packages included, the SNMP sub-system will read the snmpd.conf file from the location specified in SNMPCONFPATH, or the standard builtin locations, and use these profiles. Only the profiles specified in the ACCESS-CONTROL section of snmpd.conf file have been tested and shown to work. Other profiles which have been implemented in UCD-SNMP-4.1.2's snmpd.conf may not work because the sole purpose of adding support for the snmpd.conf file has been to set up ACCESS-CONTROL models.

At startup, the SNMP module tries to look for file snmp.conf. If this file is not available, the module successively looks for files snmpd.conf, snmp.local.conf and snmpd.local.conf at the locations pointed to by SNMPCONFPATH environment variable. In case SNMPCONFPATH is not defined, the search sequence is carried out in default directories. The default directories are :/usr/share/snmp, /usr/local/share/snmp and $(HOME)/.snmp. The configurations read from these files are used to control both, SNMP applications and the SNMP agent; in the usual UNIX fashion.

The inclusion of snmpd.conf support is enabled by default when suitable filesystems and FILEIO packages are active.

2017-02-09
Documentation license for this page: Open Publication License