Can someone please explain that what are the major differences between Juniper EX4200 and Juniper EX4300 switches? Both are standard Juniper Ethernet switches but is there any situation where EX4300 fits better than EX4300 (if there is any)?
and lastly
Why Juniper need to launch EX4300 switch when EX4200 switch was already doing its job?
Thanks
If you're looking at purchasing new hardware, EX4300s are generally recommended. It's not that there's anything wrong with the EX4200, it's simply that the EX4300 is the next generation with new features, longer term support, etc.
Technically speaking, without getting into all of the finite variations on each model within both platforms, the main differences are:
EX4300s uses ELS software, which is basically just consolidating all switching syntax and functionality. EX4200s use non-ELS (considered legacy). Here's the Getting Started guide for ELS in case you're unfamiliar with the terminology.
EX4300s are Broadcom based and EX4200s are Marvell based. This may or may not be a factor for you.
EX4300s are going to have a longer hardware and software support life span, whereas EX4200 will not be kept as up to date as the EX4300.
Lastly, there are various feature differences between the two platforms. You can either check the Feature Explorer or in case you don't have luck there, ask another question.
EX4300s have four QSFP+ ports (rear panel) which may be used for stacking or as 40GbE. They also don't require an uplink module (EX-UM-xxx) and therefore have four SFP+ 1/10G ports (front panel) in the base model.
The newer software on EX4300 makes one shocking choice you need to be aware of. STP may be disabled in a factory-default configuration. That can produce accidental loops and other problems if you're not aware it's going to happen. Double-check the spanning-tree config (under protocols { ... }) before connecting an EX4300 to a production network.
I believe EX4300 fixes the worst and dumbest ASIC limitation of EX4200, too; on EX4200, glean traffic that needs to be punted to the RE, but would be dropped by lo0 filter, is therefore dropped instead of resulting in an ARP who-has going out to the connected host.
If you're happy with EX4200 then keep on running them unless your organizational needs require you to replace end-of-life equipment. The differences between 4200 and 4300 are minimal for most legacy environments. For new installations, definitely choose the 4300.
If you check the specs, there are differences in backplane capability and supported ports (128 vs 320 Gbit/s VC backplane, obsolete XFP on 4200, QSFP+ on 4300, ...).
Apart from that, every device model has to be replaced after a number of years due to manufacturing reasons. Vital parts may not be produced more, advancing semiconductor processing technology obsoletes parts, and a few hardware optimizations may be advisable - for performance and cost.
