SNMP

Simple Network Management Protocol

Online MIB Browser

http://www.oidview.com/mibs/0/HOST-RESOURCES-MIB.html - appears to have gone offline June 2020

https://bestmonitoringtools.com/mibdb/mibdb_search.php

Statistics

• Source: Manager (Poller)
• Destination: Device
• Port: 161 UDP

Traps / Alarms

• Source: Device
• Destination: Manager
• Port: 162 UDP

SNMP v3

Proviso

SNMP community string as used in the gui

&V3,[[Access Mode]]=Auth-MD5,[[Security Name]]=useridtext,[[Context Name]]=,[[Auth Passwd]]=authpwtext

SNMP Communtity string as used in the cli

snmpGet [[OID's]] sys Name.0 -S SNMPCOLLECTORNAME -P 3002 -r 3 -t 2 -c '&V3,[[AccessMode]]=Auth-MD5,[[Security Name]]=useridtext,[[Context Name]]=,[[Auth Passwd]]=authpwtext'

OIDs that use strings as the indexes

jnxSubscriberPortTerminatedCounter.3.112.115.51 = 14825

First int = length Proceeding ints, convert to hex, then hex to ascii in the example above

Length = 3
112 -> 70 -> p
115 -> 73 -> s
51 ->  33 --> 3
index = ps3

netsnmp will translate this when querying ie jnxSubscriberPortTerminatedCounter."ps3"

Net-SNMP

CLI command

./snmpget -v 3 -a MD5 -A 'authpwtext' -l authNoPriv -u useridtext 10.78.252.19 iso.3.6.1.2.1.1.5.0

Nice guide to comparing Juniper CLI to SNMP

qandaitem09186a00800b69ac.shtml www.cisco.com/en/US/tech/tk648/tk362/technologiesqandaitem09186a00800b69ac.shtml

Juniper CLI

show snmp mib walk ifDescr

Identify which net-snmp version is used in a particular Junos OS version

restart mib-process immediately

show log messages | match "NET-SNMP" | match mib2d 
May 25 07:38:15.434  jtac-lab-re0 mib2d[5920]: LIBJSNMP_NS_LOG_INFO: INFO: ns_subagent_open_session: NET-SNMP version 5.3.1 AgentX subagent Open-Sent!

Note: The command 'restart mib-process immediately' does not impact traffic. The process is respawned in seconds and during this brief time the network monitoring via SNMP is disrupted.

SNMP Version

• RFC1213 - SNMPv1
• RFC3416 - SNMPv2c
• RFC3411-3415 - SNMPv3

Grafana

Because collectd doesnt us an inventory model - it doesnt appear to keep track or report on missed polls / values. We have to figure this out at the Grafana layer - looking for nulls. Except this isnt easy, we instead have to count how many values we have. This only works for the past 7 days / your raw retention period.

Find how many null values there are (thus missed pollings) - by counting how many values we have

• Series - Choose a metric and using * for the hosts
• Functions scale(0) offset(1) summarize(1h, sum, true)

95% billing

Will put a line at 95% usage on the graph. Target: scale(8)movingAverage(5min) 95%: nPercentile(#A,95)

SNMP Simulator

Used by librenms

http://snmplabs.com/snmpsim/index.html

snmpsim-command-responder = snmpsimd.py

data/variation files installed to

• Ubuntu - /usr/local/snmpsim

python /usr/local/bin/snmpsimd.py --data-dir=/usr/local/snmpsim/data/ --variation-modules-dir=/usr/local/snmpsim/variation/ --agent-udpv4-endpoint=127.0.0.1:1024 

• Centos - /usr/snmpsim

/usr/bin/snmpsimd.py --data-dir=/usr/snmpsim/data --variation-modules-dir=/usr/snmpsim/variation --agent-udpv4-endpoint=127.0.0.1:1024

Usage

https://www.ibm.com/support/pages/how-use-snmpsim-simulate-network-device-based-snmp-walk-file