Please note that this is just the official way which JTAC supports, it does not mean that a direct upgrade from 14.1X54 to 18.1R3 does not work fine. I'd suggest you to try in your lab a direct upgrade with your current config installed. If it works fine, just upgrade directly. If not, check which configuration part is not compatible with the new JUNOS release.
You should be able to upgrade directly, the onlything you must make sure before doing that, is that the configuration running in 14.1 is compatible with 18.1. The best way to do it, is testing the configuration in a lab unit running a newer code or open a ticket with JTAC to validate the configuration.
The most common errors are interfaces referenced under protocols xstp, but the interfaces are not part of family ethernet-switching. This will cause a commit error preventing the configuration to commit, so there will be an outage.
Another problem, is that ssh root access is disable by default in new codes so you must manually specify it if need it. (#set system services ssh root-login allow)
If this solves your problem, please mark this post as "Accepted Solution"
Thank you all for your replies. Unfortunately we don’t have a lab so i had to wing it.
14.1X53-D47 -> 16.1R7-S7
Problem 1: Lost SSH to the VC because config. only loaded partially. When I tried to “commit” the config I found the problem was in the VSTP config. I had a couple interfaces configured for VSTP that were disable so they were not set as " family ethernet-switching".
[edit protocols vstp] 'interface' xSTP:Interface ge-1/0/X is not enabled for Ethernet Switching
Problem 2: After fixing the “ ethernet-switching” a second problem showed up:
[edit protocols vstp] xSTP:Trying to configure too many interfaces for given protocol
Since I had each interface added to the vstp configuration individually, what I did was remove each interface and add “protocols vstp interface all”.
Just want to inform you all, today upgraded ex4300 switch junos from 14.1X53-D30.3 to 18.1R3-S9.1 directly without following any intermediate junos and i have not faced any issues during/after the upgrade.
As you all mentioned in your post, i verified SSH, Telnet and other services too. Everything looks normal, If anyone would prefere to upgrade directlty from 14.1x to 18.1 series you can upgraded it as per my understanding. Below output fyr.
fpc0: -------------------------------------------------------------------------- Information for snapshot on internal (/dev/da0s1a) (primary) Creation date: Jul 10 16:46:53 2020 JUNOS version on snapshot: jcrypto-ex: 18.1R3-S9.1 jdocs-ex: 18.1R3-S9.1 jsd : powerpc-18.1R3-S9.1-jet-1 jsdn-powerpc: 18.1R3-S9.1 junos : ex-18.1R3-S9.1 junos-ex-4300: 18.1R3-S9.1 jweb-ex: 18.1R3-S9.1 Information for snapshot on internal (/dev/da0s2a) (backup) Creation date: Nov 13 08:48:42 2015 JUNOS version on snapshot: jdocs-ex: 14.1X53-D30.3 junos : ex-14.1X53-D30.3 junos-ex-4300: 14.1X53-D30.3 jweb-ex: 14.1X53-D30.3
I have done the snapshot match to keep the same version in both Primary & Backup partition.