Hello My friends..?
so i have mikrotik crs354-48g-4s+2q+rm with MIPSBE arch so i wounder if i can use it as a core router instead of purchasing a new Router, so is it fine ..?
i mean if i put a firewall rules on it, also some pppoe acounts and other thing..etc. Is there is a probability that the CPU will reach a high level when the network will become active ..?
anyone try to use it in that way..?

Depends...
What is the PPPoE link ? 100Mbit ? 1000MBits ?? If only a 100Mbits Internet link I would risk ik. Don't expect 500Mbps Internet performance or something...
Your product is a SWITCH with a pretty weak CPU, so if you start using as a breakout-router to Internet don't expect a lot of performance.

This device is called a switch, with a ROS installed.
As a router its capabilities are very modest at the level of HAP or HAP ac lite

This device is called a switch, with a ROS installed.
As a router its capabilities are very modest at the level of HAP or HAP ac lite

in a deep view what is the thing that make router router ..?
i mean what Router can do and switch can not and visa versa..?

A router would have a more powerful CPU for a start. And more RAM.

The CRS 354 only has a single core CPU running at 650Mhz with only 64MB of RAM.

You can see the performance yourself on the product page:

https://mikrotik.com/product/crs354_48g ... estresults

410Mbps with 25 rules. I imagine those testing conditions would have been ideal to get those results.

A router's main objective is to establish a connection between various networks in a simultaneous manner and it works on the network layer.

A switch's main objective is to establish a simultaneous connection among various devices.

Some Switches have the ability to act both as a Switch and a Router and those specific units have the effective processing power

The CRS 354-48g-4s+2q+rm -- because of the OS called RouterOS -- can be utilized as a Switch and Router BUT does not have the effective CPU processing power to handle any significant routing LOADS. As A Switch it can be effective since much of the switching function can be hardware accelerated but there is no hardware acceleration for the Routing function so the routing is depended on the CPU and this CPU is on the weak side for ROUTING under load

Switches that can Handel both Routing and Switching effectively have specialized ASICS to do the Switching/Routing job properly --- those kind of switches cost a lot more money.

Good Learning link
https://www.softwaretestinghelp.com/lay ... -switches/

i mean what Router can do and switch can not and visa versa..?

As a switch it can "total non-blocking throughput is 168 Gbps, switching capacity is 336 Gbps"
As a router it can "the forwarding rate reaches 235 Mpps"
As you have already been told, if you are satisfied with the speed of the Internet 100 mbps then it can be used as a router