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[Junos] SNMP start-up traps: cold-start and warm-start

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Article ID: KB30493 KB Last Updated: 28 Jun 2018Version: 4.0
Summary:

This article describes the conditions of generating a cold-start trap with the request system reboot command. As with the other traps, this depends on SNMPD, but in this article, we can see how SNMPD determines whether the cold-start or warm-start trap should be generated.

Symptoms:

In a Juniper router, a cold-start trap is generated by SNMPD when the system comes up from a power cycle, while a warm-start trap is generated when the system comes up from a software reset. Under certain conditions, however, a Juniper router generates a cold-start trap even when the router is restarted with the request system reboot CLI command, which should cause a router software reset.

Cause:

Before Junos OS 17.2R2, if the SNMPD is restarted within the predefined cut-off time of 300 seconds from system boot time, the SNMPD generates a cold-start trap instead of generating a warm-start trap. You can also see a cold-start trap if you restart SNMPD within 300 seconds after the Routing Engine is booted.

Here's the operation log to see a cold-start trap by restarting SNMPD:

lab@router-re0> request system reboot both-routing-engines
Reboot the system ? [yes,no] (no) yes

Rebooting re1

*** FINAL System shutdown message from lab@router-re0 ***

System going down IMMEDIATELY

Shutdown NOW!
[pid 2279]

*** messages ***
Jul 24 14:46:52.170 router-re0 mgd[2252]: UI_CMDLINE_READ_LINE: User 'id', command 'request system reboot both-routing-engines '
Jul 24 14:46:54.362 router-re0 mgd[2252]: UI_REBOOT_EVENT: System rebooted by 'id'
Jul 24 14:46:54.625 router-re0 Jul 24 14:46:54.625 rollpanna-re1 mgd[2153]: UI_REBOOT_EVENT: System rebooted by 'root'
Jul 24 14:46:54.716 router-re0 mgd[2252]: UI_CHILD_START: Starting child '/sbin/shutdown'
Jul 24 14:46:54.745 router-re0 mgd[2252]: UI_CHILD_STATUS: Cleanup child '/sbin/shutdown', PID 2276, status 0
-- snip --
Jul 24 14:52:33.905 router-re0 snmpd[1804]: SNMPD_TRAP_QUEUED: Adding trap to xxx.xxx.xxx.xxx to throttle queue, 1 traps in queue
Jul 24 14:52:33.907 router-re0 snmpd[1804]: SNMPD_TRAP_COLD_START: trap_generate_cold: SNMP trap: cold start
-- snip --
Jul 24 14:52:47.725 router-re0 snmpd[2001]: SNMPD_TRAP_QUEUED: Adding trap to xxx.xxx.xxx.xxx to throttle queue, 1 traps in queue
Jul 24 14:52:47.725 router-re0 snmpd[2001]: SNMPD_TRAP_COLD_START: trap_generate_cold: SNMP trap: cold start

router-re0 (ttyp2)

login:
Password:

#################### system uptime << 300 seconds; cold start trap ####################

lab@router-re0> show system uptime
Current time: 2015-07-24 14:53:03 JST
System booted: 2015-07-24 14:48:26 JST (00:04:37 ago) <-- Less than 300 seconds
Protocols started: 2015-07-24 14:52:38 JST (00:00:25 ago)
Last configured: 2015-07-24 14:28:42 JST (00:24:21 ago) by lab
2:53PM up 5 mins, 2 users, load averages: 2.48, 0.87, 0.36

lab@router-re0> restart snmp
Jul 24 14:53:17
Simple Network Management Protocol process started, pid 2047

*** messages ***
Jul 24 14:53:12.216 router-re0 mgd[1951]: UI_CMDLINE_READ_LINE: User 'id', command 'restart snmp '
Jul 24 14:53:12.219 router-re0 mgd[1951]: UI_RESTART_EVENT: User 'id' restarting daemon 'Simple Network Management Protocol process'
Jul 24 14:53:12.222 router-re0 init: snmp (PID 2001) terminated by signal number 15!
Jul 24 14:53:12.222 router-re0 init: snmp (PID 2047) started
Jul 24 14:53:12.226 router-re0 mgd[1951]: UI_COMMIT_PROGRESS: Commit operation in progress: signaling 'Init daemon', pid 1, signal 1, status 0 with notification errors enabled
Jul 24 14:53:17.272 router-re0 snmpd[2047]: SNMPD_TRAP_QUEUED: Adding trap to xxx.xxx.xxx.xxx to throttle queue, 1 traps in queue
Jul 24 14:53:17.272 router-re0 snmpd[2047]: SNMPD_TRAP_COLD_START: trap_generate_cold: SNMP trap: cold start <<<<<<<<<< cold start trap


#################### system uptime >> 300 seconds; warm start trap ####################

lab@router-re0> show system uptime
Jul 24 14:53:42
Current time: 2015-07-24 14:53:42 JST
System booted: 2015-07-24 14:48:26 JST (00:05:16 ago) <-- Greater than 300 seconds
Protocols started: 2015-07-24 14:52:38 JST (00:01:04 ago)
Last configured: 2015-07-24 14:28:42 JST (00:25:00 ago) by lab
2:53PM up 5 mins, 2 users, load averages: 2.86, 1.19, 0.50

lab@router-re0> restart snmp
Jul 24 14:53:48
Simple Network Management Protocol process started, pid 2144

Jul 24 14:53:48.284 router-re0 mgd[1951]: UI_CMDLINE_READ_LINE: User 'id', command 'restart snmp '
Jul 24 14:53:48.284 router-re0 mgd[1951]: UI_RESTART_EVENT: User 'id' restarting daemon 'Simple Network Management Protocol process'
Jul 24 14:53:48.287 router-re0 init: snmp (PID 2047) terminated by signal number 15!
Jul 24 14:53:48.287 router-re0 init: snmp (PID 2071) started
Jul 24 14:53:48.293 router-re0 mgd[1951]: UI_COMMIT_PROGRESS: Commit operation in progress: signaling 'Init daemon', pid 1, signal 1, status 0 with notification errors enabled
Jul 24 14:53:48.372 router-re0 snmpd[2071]: SNMPD_TRAP_WARM_START: trap_generate_warm: SNMP trap: warm start <--- warm start trap
Solution:

Before Junos OS 17.2R2, a cold-start trap is sent if the SNMP restarts within the predefined cut-off time 300 seconds from the system reboot, and if the SNMP restarts after this cut-off time from the system reboot, it is assumed that the SNMPD is manually restarted and a warm-start trap is sent.

  • If the system uptime is less than 300 seconds, Junos sends a cold-start trap when the SNMPD process is restarted.

  • If the system uptime is greater than 300 seconds, Junos sends a warm-start trap when the SNMPD process is restarted.

However, in case the system takes more time to boot, then there is a chance that the SNMPD starts after 300 seconds and a warm-start trap is sent in place of cold-start trap. This behavior is changed from Junos OS 17.2R2. Starting from Junos OS 17.2R2, the SNMPD sends a cold/warn trap based on the actual reason of the SNMPD restart rather than using a cutoff time of 300 seconds which might not hold good if the boot time varies. A file is implemented to decide whether to send a cold-start trap or warm-start trap. In this code change, the SNMPD maintains a file /var/db/snmp_cold_start.time which maintains the last sent cold-start trap timestamp.

  • If the system reboot time is older than the time in this file, then the cold-start trap is already sent and now the warm-start trap has to be sent.

  • If the time in the file is older than the system reboot time, then this is a cold-start trap which was sent before the system reboot, and now we have to send the cold-start trap and update the file with the latest cold-start trap timestamp.

Note that POST (Power On Self Test) is commonly performed upon cold-start. But on a Juniper router, POST is performed regardless of whether it is restarted by a power cycle (cold-start) or software reset (warm-start).

Modification History:

2018-06-28: Minor non-technical edits.
2017-05-26: Modified version info from 17.3 to 17.2R2
2017-05-08: Added details about behavior changes in Junos 17.3

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