Manual Pages for UNIX Darwin command on man snmpusm

SNMPUSM(1) Net-SNMP SNMPUSM(1)

NAME

snmpusm - creates and maintains SNMPv3 users on a network entity

SYNOPSIS

ssnnmmppuussmm [COMMON OPTIONS] ccrreeaattee USER [CLONEFROM-USER]

ssnnmmppuussmm [COMMON OPTIONS] ddeelleettee USER

ssnnmmppuussmm [COMMON OPTIONS] cclloonneeFFrroomm USER CLONEFROM-USER

ssnnmmppuussmm [COMMON OPTIONS] [-Ca] [-Cx] ppaasssswwdd OLD-PASSPHRASE NEW-

PASSPHRASE [USER]

ssnnmmppuussmm [COMMON OPTIONS] <-Ca | -Cx> -Ck ppaasssswwdd OLD-LOCALIZED-KEY NEW-

PASSPHRASE [USER]

ssnnmmppuussmm [COMMON OPTIONS] [-Ca] [-Cx] cchhaannggeekkeeyy [[UUSSEERR]]

DESCRIPTION

ssnnmmppuussmm is an SNMP application that can be used to do simple mainte-

nance on the users known to an SNMP agent, by manipulating the agent's

User-based Security Module (USM) table. The user needs write access to

the usmUserTable MIB table. This tool can be used to create, delete, clone, and change the passphrase of users configured on a running SNMP agent. OOPPTTIIOONNSS

-CCaa Change the authentication key.

-CCxx Change the privacy key.

-CCkk Use old localized key instead of old passphrase. When this

option is used, either the -Ca or -Cx (but not both) option must

also be used. CCRREEAATTIINNGG UUSSEERRSS An unauthenticated SNMPv3 user can be created using the command ssnnmmppuussmm create USER This constructs an (inactive) entry in the usmUserTable, with no authentication or privacy settings. In principle, this user should be

useable for 'noAuthNoPriv' requests, but in practise the Net-SNMP agent

will not allow such an entry to be made active. In order to activate this entry, it is necessary to "clone" an existing user, using the command

ssnnmmppuussmm cloneFrom USER CLONEFROM-USER

The USER entry then inherits the same authentication and privacy set-

tings (including pass phrases) as the CLONEFROM user. These two steps can be combined into one, by using the command

ssnnmmppuussmm create USER CLONEFROM-USER

The two forms of the ccrreeaattee sub-command require that the user being

created does not already exist. The cclloonneeFFrroomm sub-command requires

that the user being cloned to does already exist. Cloning is the only way to specify which authentication and privacy protocols to use for a given user, and it is only possible to do this once. Subsequent attempts to reclone onto the same user will appear to

succeed, but will be silently ignored. This (somewhat unexpected) be-

haviour is mandated by the SNMPv3 USM specifications (RFC 2474). To change the authentication and privacy settings for a given user, it is necessary to delete and recreate the user entry. This is not necessary for simply changing the pass phrases (see below). This means that the agent must be initialized with at least one user for each combination of authentication and privacy protocols. See the snmpd.conf(5) manual page for details of the ccrreeaatteeUUsseerr configuration directive. DDEELLEETTIINNGG UUSSEERRSS A user can be deleted from the usmUserTable using the command ssnnmmppuussmm delete USER CCHHAANNGGIINNGG PPAASSSS PPHHRRAASSEESS User profiles contain private keys that are never transmitted over the wire in clear text (regardless of whether the administration requests

are encrypted or not). To change the secret key for a user, it is nec-

essary to specify the user's old passphrase as well as the new one. This uses the command

ssnnmmppuussmm [-Ca] [-Cx] passwd OLD-PASSPHRASE NEW-PASSPHRASE [USER]

After cloning a new user entry from the appropriate template, you should immediately change the new user's passphrase. If USER is not specified, this command will change the passphrase of

the (SNMPv3) user issuing the command. If the -Ca or -Cx options are

specified, then only the authentication or privacy keys are changed. If these options are not specified, then both the authentication and privacy keys are changed.

ssnnmmppuussmm [-Ca] [-Cx] changekey [USER]

This command changes the key in a perfect-forward-secrecy compliant way

through a diffie-helman exchange. The remote agent must support the

SNMP-USM-DH-OBJECTS-MIB for this command to work. The resulting keys

are printed to the console and may be then set in future command invo-

cations using the -defAuthLocalizedKey and -defPrivLocalizedKey

options or in your snmp.conf file using the defAuthLocalizedKey and defPrivLocalizedKey keywords. Note that since these keys are randomly generated based on a diffie helman exchange, they are no longer derived from a more easily typed password. They are, however, much more secure.

To change from a localized key back to a password, the following vari-

ant of the ppaasssswwdd sub-command is used:

ssnnmmppuussmm <-Ca | -Cx> -Ck passwd OLD-LOCALIZED-KEY NEW-PASSPHRASE

[USER]

Either the -Ca or the -Cx option must be specified. The OLD-LOCALIZED-

KEY parameter is the localized key that was printed out by the

cchhaannggeekkeeyy sub-command.

EEXXAAMMPPLLEESS

Let's assume for our examples that the following VACM and USM configu-

rations lines were in the snmpd.conf file for a Net-SNMP agent. These

lines set up a default user called "initial" with the authentication passphrase "setuppassphrase" so that we can perform the initial setup of an agent:

# VACM configuration entries

rwuser initial

# lets add the new user we'll create too:

rwuser wes

# USM configuration entries

createUser initial MD5 setuppassphrase DES Note: the "initial" user's setup should be removed after creating a real user that you grant administrative privileges to (like the user "wes" we'll be creating in this example. Note: passphrases must be 8 characters minimum in length. CCrreeaattee aa nneeww uusseerr

snmpusm -v3 -u initial -n "" -l authNoPriv -a MD5 -A setuppassphrase

localhost create wes initial Creates a new user, here named "wes" using the user "initial" to do it. "wes" is cloned from "initial" in the process, so he inherits that user's passphrase ("setuppassphrase"). CChhaannggee tthhee uusseerr''ss ppaasssspphhrraassee

snmpusm -v 3 -u wes -n "" -l authNoPriv -a MD5 -A setuppassphrase

localhost passwd setuppassphrase newpassphrase After creating the user "wes" with the same passphrase as the "initial" user, we need to change his passphrase for him. The above command changes it from "setuppassphrase", which was inherited from the initial user, to "newpassphrase". TTeesstt tthhee nneeww uusseerr

snmpget -v 3 -u wes -n "" -l authNoPriv -a MD5 -A newpassphrase local-

host sysUpTime.0 If the above commands were successful, this command should have properly performed an authenticated SNMPv3 GET request to the agent. Now, go remove the vacm "group" snmpd.conf entry for the "initial" user

and you have a valid user 'wes' that you can use for future transac-

tions instead of initial. WWAARRNNIINNGG Manipulating the usmUserTable using this command can only be done using

SNMPv3. This command will not work with the community-based versions,

even if they have write access to the table.