The Article provides solution to the login issue seen on Device after it was upgraded from Junos 14.1X to 18.4X

Customer reported that they were not able to login into the device using any credentials after upgrading device from 14.x to 18.x version .

When the device was being upgraded , the message "mgd: error: commit failed: (statements constraint check failed)"was seen.

<<<<>>>>>

FILE SYSTEM CLEAN; SKIPPING CHECKS

clean, 515205 free (21 frags, 64398 blocks, 0.0% fragmentation)

Marker feature is not supportedMarker feature is not supportedln: /var/db/scripts/import: No such file or directory

Mounted junos-openconfig package on /dev/md15...
........
kern.timecounter.hardware: ACPI-safe -> TSC

chmod: /var/db/scripts/: No such file or directory

fxbcm0: <FX TOR BCM> mem 0xfeb00000-0xfeb3ffff irq 11 at device 8.0 on pci0

fxbcm0: fxbcm: registers at 0xf7b5e000

fx_scpld0 on fxcb_fpga1 

pci-hgcomdev module loadedhgcommdev0: <HGCOMMDEV For Host VM communication> mem 0xfebc1000-0xfebc1fff at device 22.0 on pci0

hgcommdev0: hgcommdev: registers at 0xf7b9e000

Create /var/db/scriptCreating initial configuration...Kernel out of physical pages (error count: 1)
[edit vlans default l3-interface]
 'l3-interface irb.0'
  Interface must already be defined under [edit interfaces]
mgd: error: commit failed: (statements constraint check failed)
Warning: Commit failed, activating partial configuration.
Warning: Edit the router configuration to fix these errors. <><<<<<Warning shown in bootup logs
.........
Setting initial options: debugger_on_panic=NO debugger_on_break=YES.

Starting optional daemons: kdmmachdep.do_minidump: 1 -> 1
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During the lab test when the device was  upgraded from 14.x to 18.x ,similar login issue was observed.

With  "root"  user login to  the device was successful but it takes the device into amnesiac  mode and below  configuration difference seen between 14.x and 18.x

In 14.x Junos the l3-interface is accepted even without irb interface configuration so no warning message is seen 

default {
  vlan-id 1;
  l3-interface irb.0;
} 

In 18.x without irb interface configuration, the warning message was seen and eventually configuration was rejected

default {
  vlan-id 1;

  ##
  ## Warning: Interface must already be defined under [edit interfaces]
  ##                  
  l3-interface irb.0;         
}  

As there is a configuration mismatch between Junos 14.x and 18.x , we can follow below solution to recover.

Solution 1:

Delete "l3-interface irb.0"  statement used if the irb is not required.

Solution 2:

If the irb interface is required , then define irb.0 under [edit interfaces] hierarchy, then commit the configuration

Example:

[edit interfaces]

labroot@R1#  set interfaces irb unit 0 family inet <ip address>

 

NOTE:

Based on the investigation it is found that when there is a config  mismatch during the upgrade the commit fails, because of it authentication related config does not get committed. As the authentication config files are incorrect, login fails.
 

In general the commit failure  seen during the upgrade to be corrected to get successful login of the device after upgrade.