The document describes four methods for remotely executing commands on a monitored server from a monitoring server: 1. Using SNMP extend over UDP, which is stateless and insecure. 2. Using NRPE over TCP, which provides reliability and security through connection orientation. 3. Using SSH to call binaries or scripts directly over TCP, with reliability and security. 4. Extending SSH to first transfer binaries or scripts to the monitored server, then calling and deleting them to provide code execution capabilities remotely in a secure manner.

1. Remote execution using extend in Net-SNMP
Monitoring server UDP
Observed server
(stateless / unreliable / secured in v3)
process context monitoring application process context - SNMP agent
SNMP Monitor Net-SNMP agent
script
mapping SNMP-OID to
call remote OID SNMP request
command <args []>
command <args[]>
command
Port 161
Test
verify result result
result and values
Service state
Up/Down
created 21.06.2010 – ronny@opennms.org

2. Remote execution using NRPE
Monitoring server TCP
Observed server
(reliable / connection oriented / secured)
process context monitoring application process context - NRPE agent
NRPE Monitor NRPE agent
script
call NRPE describer with args
mapping describer to
call remote
command <args []>
command <args[]>
command
Port 5666
Test
verify result result
result and values
Service state
Up/Down
created 21.06.2010 – ronny@opennms.org

3. Remote execution using Secure Shell
Monitoring server TCP
Observed server
(reliable / connection oriented / secured)
process context monitoring application process context - SSH user
General Purpose Monitor SSH-Server
script
call remote call binary / script
command <args[]>
command
Port 22
Test
verify result result
result and values
Service state
Up/Down
created 21.06.2010 – ronny@opennms.org

4. Remote execution using Secure Shell
extended with code transfer
Monitoring server TCP
Observed server
(reliable / connection oriented / secured)
process context monitoring application process context - SSH user
General Purpose Monitor SSH-Server
script
temp.
copy binary or script transfer binary / script script
call remote call binary / script
command <args[]>
command
Port 22
Test
verify result result
result and values
delete remote
delete binary / script delete
command
script
Service state
Up/Down
created 21.06.2010 – ronny@opennms.org