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Full Discussion: SNMP Community String ???
Special Forums IP Networking SNMP Community String ??? Post 10923 by Neo on Saturday 24th of November 2001 05:38:36 PM
Old 11-24-2001
If you look at network devices as clients and devices that received SNMP traps or poll devices as servers then the community string is the same as apassword that the server issues to the client device during a remote query. The string can be just about anything reasonable, as long as the client and the server use the same community strings.

Most network devices allow different levels of SNMP access, for example: READ ONLY or READ/WRITE. Each one of these levels of access would/should have a different (hard to guess) community string.

When a client sends an SNMP trap to a server receiving SNMP trap information, the SNMP community string is not required.

However, some devices use the SNMP community string as a password for terminal (serial and monitor) access to the device as well. Don't just change them and forget them Smilie

That is just about it........ the poster stated that the device was only sending traps, so the community string is not so important between client-server (no server queries to the client device) but should be changed for security reasons so something other than the default value, i.e. public.... Make sure you document the change somewhere safe so if you forget to tell the next responsible person after you leave the project, they will have a roadmap of the changes you made!

However, never fear... most SNMP community strings can be reset from the console/monitor of the device (or with physical access to the device). Yet, if you have hundreds of devices..... depending on this technique (physical access to reset) is not a good idea Smilie
 

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snmpd(8n)																 snmpd(8n)

Name
       snmpd - Simple Network Management Protocol (SNMP) Agent for ULTRIX gateways and hosts

Syntax
       /etc/snmpd [ -d debuglevel logfile ]

Description
       The  SNMP  Agent,  performs SNMP operations on an ULTRIX gateway or host.  The daemon, which is started up by an entry in the file, sits in
       the background and listens on SNMP port 161.  When the daemon receives an SNMP packet from a Network Management Station (NMS),  the  daemon
       performs SNMP operations on the packet and returns a valid response to the NMS.

       The  daemon extracts much of its information from kernel memory.  Static variables whose values are not available in the kernel take values
       from the SNMP configuration file,

   SNMP Trap Support
       The cold start and authentication failure trap types are supported by

       The cold start trap type is generated by when is restarted.  The authentication failure trap type is generated when an attempt at  using  a
       community fails.  The attempt fails when an unauthorized client tries to use or the community is used in a way that the community type does
       not allow.

       The daemon sends traps to all communities specified in the configuration file with a community type

       The default is for the daemon to generate authentication failure traps.	However, if the following clause is  specified	somewhere  in  the
       file, authentication failure traps are not generated:
       no_authen_traps

   SNMP Sets
       When  the  daemon receives a set-request packet, it processes the variables in the packet and verifies that they are valid read-write vari-
       ables.  While performing this verification, the daemon constructs a linked list of the set requests.  After it has completed the  verifica-
       tion,  it performs the actual set operations on the variables, as if they were being performed simultaneously.  If any actual set operation
       fails, all of the previous set variables from the set-request packet are restored to their old values.

   SNMP Supported Variables
       For a complete listing of the SNMP Management Information Base (MIB) variables that are supported, see the Guide to Networking.

Options
       By default, the daemon uses the command to record its error messages.  However, you can obtain certain debugging and trace  information	by
       specifying the flag, the appropriate debug level, and a log file for the output on the command line.

       -d debuglevel logfile
	    Outputs debugging and trace information.

       You can specify any one of the following debug levels with the flag:

       1    Print  the version number, start time, and exit time of Also print out when an SNMP packet is received, the address of the sender, and
	    the packet size in bytes.

       2    Print out what the daemon has read from the file.

       3    Dump the SNMP packet that the daemon has just received and is about to process.  Also print out the route and interface  address  that
	    the  daemon  is  currently	looking  up.  This debug level also dumps the SNMP packet that the server is sending back in response to a
	    received SNMP message.

       4    Dump the variable tree.  Also print out the static bootstrap array of tree information.

       The output for a debug level includes the information for all levels including and below the level that you specify.  For example,  if  you
       specify a debug level of 3, your output includes debug information for levels 3, 2, and 1.

       If no debug levels are set, detaches itself from the controlling terminal and executes in the background.

Restrictions
       Not all of the MIB variables are supported.

       Only the variable is settable.

Files
	    SNMP configuration file

See Also
       snmpext(3n), snmpd.conf(5n), snmpsetup(8n)
       RFC 1066--Management Information Base for Network Management of TCP/IP-based Internets
       RFC 1067--A Simple Network Management Protocol
       Guide to Networking

																	 snmpd(8n)
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