Simulating SNMP Agents#
The snmpsim-command-responder program performs actual SNMP agent simulation
based on the simulation data provided.
Simulation Data#
SNMP agents simulation data ends up in .snmprec files. Once SNMP request comes in, SNMP Simulator constructs .snmprec file path and tries to locate it by searching through the following directories:
~/.snmpsim/data/usr/local/share/snmpsim/data{python-package-root}/data
On Windows search paths are:
\Document and Settings\{user}\Application Data\SNMP Simulator\Data\Program Files\SNMP Simulator\Data{python-package-root}/data
These directories are searched in the specified order till the first match.
For example, a set up collection of .snmprec files would look like:
$ cd /usr/local/share
$ find snmpsim/data
snmpsim/data
snmpsim/data/public.snmprec
snmpsim/data/mib2dev
snmpsim/data/mib2dev/ip-mib.snmprec
snmpsim/data/mib2dev/host-resources-mib.snmprec
snmpsim/data/mib2dev/tcp-mib.snmprec
snmpsim/data/foreignformats
snmpsim/data/foreignformats/linux.snmpwalk
snmpsim/data/foreignformats/winxp.sapwalk
snmpsim/data/variation
snmpsim/data/variation/subprocess.snmprec
snmpsim/data/variation/virtualtable.snmprec
snmpsim/data/recorded
snmpsim/data/recorded/linksys-system.snmprec
snmpsim/data/recorded/udp-endpoint-table-walk.snmprec
...
Note
The --data-dir option can be used to prepend custom directories to the
search path. However, if SNMP engine is configured explicitly (via the
--v3-engine-id option), then custom data directories will override the
default search path.
SNMP Simulator Daemon#
The snmpsim-command-responder tool hosts multiple independent SNMP Command
Responders. It can run multiple SNMP engines exchanging data over multiple
network interfaces. Each SNMP engine instance can serve many independent sets of
SNMP management objects sourced from local .snmprec files or
variation modules.
Multiple Network Interfaces#
SNMP Simulator daemon can listen at multiple local IP interfaces and/or UDP
ports. Just pass multiple --agent-udpv4-endpoint/--agent-udpv6-endpoint
command line parameters carrying addresses to listen on. Whenever you wish
Simulator to listen on thousands of local interfaces and/or ports, use the
--agent-udpv4-endpoints-list/--agent-udpv6-endpoints-list options. These
options expect to refer to a plain text file containing newline-separated list
of transport endpoints for Simulator to listen on.
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:1611 \
--agent-udpv6-endpoint='[::1]:1161'
Scanning "/home/user/.snmpsim/variation" directory for variation modules...
no directory
Scanning "/usr/local/share/snmpsim/variation" directory for variation modules...
8 more modules found
Initializing variation modules:
notification... OK
sql... FAILED: database type not specified
numeric... OK
subprocess... OK
delay... OK
multiplex... OK
error... OK
writecache... OK
Scanning "/home/user/.snmpsim/data" directory for *.snmpwalk, *.MVC,
*.sapwalk, *.snmprec, *.dump data files... no directory
Scanning "/usr/local/share/snmpsim/data" directory for *.snmpwalk,
*.MVC, *.sapwalk, *.snmprec, *.dump data files...
==================================================================
Index /tmp/snmpsim/usr_local_share_snmpsim_data_public.dbm does not exist
for data file data/public.snmprec
Building index /tmp/snmpsim/usr_local_share_snmpsim_data_public.dbm for data
file /usr/local/share/snmpsim/data/public.snmprec (open flags "n")......
133 entries indexed
Data file /usr/local/share/snmpsim/data/public.snmprec, dbhash-indexed, closed
SNMPv1/2c community name: public
SNMPv3 context name: 4c9184f37cff01bcdc32dc486ec36961
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Index /tmp/snmpsim/usr_local_share_snmpsim_data_recorded_linksys-system.dbm
does not exist for data file /usr/local/share/snmpsim/data/recorded/
linksys-system.snmprec
Building index /tmp/snmpsim/usr_local_share_snmpsim_data_recorded_linksys-
system.dbm for data file /usr/local/share/snmpsim/data/recorded/linksys-
system.snmprec (open flags "n")......6 entries indexed
Data file /usr/local/share/snmpsim/data/recorded/linksys-system.snmprec,
dbhash-indexed, closed
SNMPv1/2c community name: recorded/linksys-system
SNMPv3 context name: 1a764f7fd0e7b0bf98bada8fe723e488
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
...
...
SNMPv3 credentials:
Username: simulator
Authentication key: auctoritas
Authentication protocol: MD5
Encryption (privacy) key: privatus
Encryption protocol: DES
Listening at:
UDP/IPv4 endpoint 127.0.0.1:1611, transport ID 1.3.6.1.6.1.1.0
UDP/IPv6 endpoint ::1:1161, transport ID 1.3.6.1.2.1.100.1.2.0
Note
An unprivileged port 1611 has been chosen in this example to avoid
running snmpsim-command-responder process as root.
By this point you can run you favorite SNMP Manager to talk to either of the two simulated devices through whatever transport you prefer. For instance, to talk to simulated Linux box over SNMP v2c through UDP over IPv4 run:
$ snmpwalk -On -v2c -c recorded/linksys-system localhost:1161 1.3.6
.1.3.6.1.2.1.1.1.0 = STRING: BEFSX41
.1.3.6.1.2.1.1.2.0 = OID: .1.3.6.1.4.1.3955.1.1
.1.3.6.1.2.1.1.3.0 = Timeticks: (638239) 1:46:22.39
.1.3.6.1.2.1.1.4.0 = STRING: Linksys
.1.3.6.1.2.1.1.5.0 = STRING: isp-gw
.1.3.6.1.2.1.1.6.0 = STRING: 4, Petersburger strasse, Berlin, Germany
.1.3.6.1.2.1.1.8.0 = Timeticks: (4) 0:00:00.04
.1.3.6.1.2.1.1.8.0 = No more variables left in this MIB View
...
To walk simulated 3com switch over SNMPv3 we’d run:
$ snmpwalk -On -v3 -n recorded/linksys-system \
-l authPriv -u simulator -A auctoritas -X privatus \
localhost:1161 1.3.6
.1.3.6.1.2.1.1.1.0 = STRING: BEFSX41
.1.3.6.1.2.1.1.2.0 = OID: .1.3.6.1.4.1.3955.1.1
.1.3.6.1.2.1.1.3.0 = Timeticks: (638239) 1:46:22.39
.1.3.6.1.2.1.1.4.0 = STRING: Linksys
.1.3.6.1.2.1.1.5.0 = STRING: isp-gw
.1.3.6.1.2.1.1.6.0 = STRING: 4, Petersburger strasse, Berlin, Germany
.1.3.6.1.2.1.1.8.0 = Timeticks: (4) 0:00:00.04
.1.3.6.1.2.1.1.8.0 = No more variables left in this MIB View
...
Note
The -n <snmp-context> parameter passed to the snmpwalk tool
addresses specific simulated device at SNMP Simulator daemon.
Multiple USM Users#
It is also possible to configure many SNMPv3 (USM) users to Simulator. Each
set of --v3-user, --v3-auth-key, --v3-priv-key parameters adds one
SNMPv3 user to Simulator.
There is no correlation between SNMPv3 users and simulated resources, all users have the same view of the Simulator and the same access permissions. But you can use SNMPv3 contextNames and/or transport endpoints for addressing different data files e.g. simulated SNMP agents.
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1 \
--v3-user=wallace --v3-auth-key=testkey123 --v3-priv-key=testkey839 \
--v3-user=gromit --v3-auth-key=testkey564 --v3-priv-key=testkey6534
Scanning "/home/user/.snmpsim/variation" directory for variation modules...
...
SNMPv3 EngineID 0x80004fb8056372617927fb76cc
------------------------------------------------------------------
SNMPv3 USM SecurityName: wallace
SNMPv3 USM authentication key: testkey123, authentication protocol: MD5
SNMPv3 USM encryption (privacy) key: testkey839, encryption protocol: DES
------------------------------------------------------------------
SNMPv3 USM SecurityName: gromit
SNMPv3 USM authentication key: testkey564, authentication protocol: MD5
SNMPv3 USM encryption (privacy) key: testkey6534, encryption protocol: DES
Listening at UDP/IPv4 endpoint 127.0.0.1:161, transport ID 1.3.6.1.6.1.1.0
...
SNMP simulator supports many SNMPv3 authentication and encryption algorithms. For each user you can configure any authentication and any encryption (privacy) algorithm.
The following authentication algorithms are currently supported (via
--v3-auth-proto=<ID> option):
ID |
Algorithm |
Reference |
NONE |
RFC3414 |
|
MD5 |
HMAC MD5 |
RFC3414 |
SHA |
HMAC SHA-1 128 |
RFC3414 |
SHA224 |
HMAC SHA-2 224 |
RFC7860 |
SHA256 |
HMAC SHA-2 256 |
RFC7860 |
SHA384 |
HMAC SHA-2 384 |
RFC7860 |
SHA512 |
HMAC SHA-2 512 |
RFC7860 |
The following privacy (encryption) algorithms are currently supported (via
--v3-priv-proto=<ID> option):
ID |
Algorithm |
Reference |
NONE |
RFC3414 |
|
DES |
DES |
RFC3414 |
AES |
AES CFB 128 |
RFC3826 |
AES192 |
AES CFB 192 |
RFC Draft |
AES256 |
AES CFB 256 |
RFC Draft |
AES192BLMT |
AES CFB 192 Blumenthal |
RFC Draft |
AES256BLMT |
AES CFB 256 Blumenthal |
RFC Draft |
3DES |
Triple DES EDE |
RFC Draft |
Note
The AES192, AES256 and 3DES are implemented based on Blumenthal and Reeder draft RFCs.
Another configurable parameter is SNMPv3 snmpEngineId value. It’s normally automatically generated but can also be configured through command line.
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1 \
--v3-engine-id=010203040505060809
Scanning "/home/user/.snmpsim/variation" directory for variation modules...
...
SNMPv3 EngineID 0x010203040505060809
------------------------------------------------------------------
SNMPv3 USM SecurityName: simulator
SNMPv3 USM authentication key: auctoritas, authentication protocol: MD5
SNMPv3 USM encryption (privacy) key: privatus, encryption protocol: DES
Listening at UDP/IPv4 endpoint 127.0.0.1:161, transport ID 1.3.6.1.6.1.1.0
Note
The SnmpEngineId value has to follow
certain format.
Multiple SNMP Engines#
SNMP Simulator could run many independent SNMP engines all within a single daemon process. SNMP managers could address particular SNMP Engine instance by querying it at a transport endpoint to which SNMP Engine is bound.
Each SNMP Engine will have its own set of USM users and could serve
its own --data-dir (or they can share a single directory).
The logic of configuring specific parameters to different SNMP engines
is to “scope” SNMP Engine parameters (like users, transports, data directory)
within its --v3-engine-id fragment of Simulator command-line sequence of
options. For example:
$ snmpsim-command-responder \
--v3-engine-id=010203040505060809 \
--v3-user=wallace --v3-auth-key=testkey123 \
--agent-udpv4-endpoint=127.0.0.1:1161 \
--v3-engine-id=090807060504030201 \
--v3-user=gromit --v3-auth-key=testkey564 \
--agent-udpv4-endpoint=127.0.0.1:1162
Scanning "/home/user/.snmpsim/variation" directory for variation modules...
...
SNMPv3 EngineID: 0x010203040505060809
------------------------------------------------------------------
SNMPv3 USM SecurityName: wallace
SNMPv3 USM authentication key: testkey123, authentication protocol: MD5
Listening at UDP/IPv4 endpoint 127.0.0.1:1161, transport ID 1.3.6.1.6.1.1.0
...
SNMPv3 EngineID: 0x090807060504030201
------------------------------------------------------------------
SNMPv3 USM SecurityName: gromit
SNMPv3 USM authentication key: testkey564, authentication protocol: MD5
Listening at UDP/IPv4 endpoint 127.0.0.1:1162, transport ID 1.3.6.1.6.1.1.1
Likewise, to make particular SNMP Engine working with specific data directory,
another, more specific, --data-dir option could be passed after the
--v3-engine-id option.
Invocation Options#
To make Simulator listening on SNMP-standard UDP port 161 on a UNIX system, you have to invoke it as root but in the same time have to specify some non-privileged UNIX user and group to switch into upon port allocation:
# snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:161 \
--process-user=simulator --process-group=simulator
On UNIX systems Simulator can be run as a daemon. Make sure to re-direct its console output into syslog:
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:161 \
--process-user=simulator --process-group=simulator \
--daemonize --logging-method=syslog:local1:debug
Logging Options#
Most of the scripts shipped with the SNMP Simulator package can log to a remote syslog server over TCP or UDP:
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:161 \
--process-user=simulator --process-group=simulator \
--daemonize --logging-method=syslog:local1:debug:192.168.1.1:514:udp
Finally, Simulator can simply log to a local log file:
$ snmpsim-command-responder --agent-udpv4-endpoint=127.0.0.1:161 \
--process-user=simulator --process-group=simulator \
--daemonize --logging-method=file:/var/log/snmpsimd.log