Three vendors, one idea, three dialects

Engineers who have only worked with one vendor often believe another is harder. Usually it is not harder, it is differently arranged. The underlying model — interfaces, addresses, routes, policies, filters — is the same everywhere, because it is defined by protocol standards rather than by any vendor.

Where the configuration lives

Cisco IOS is hierarchical by context: you enter interface configuration and issue commands that apply there. Junos is a tree you navigate and edit, then commit as a transaction. RouterOS is a set of flat lists you add items to, each with a numeric index.

The same result, expressed three ways:

# IOS
interface GigabitEthernet0/1
 ip address 10.1.1.1 255.255.255.0

# Junos
set interfaces ge-0/0/1 unit 0 family inet address 10.1.1.1/24

# RouterOS
/ip address add address=10.1.1.1/24 interface=ether1

The difference that actually matters

Not syntax — commit behaviour. On IOS, a command takes effect the moment you press enter. There is no staging and no undo. On Junos, changes accumulate as a candidate configuration and nothing happens until you commit; you can review the diff first and roll back afterwards. RouterOS applies immediately like IOS, but has safe mode, which reverts everything if your session drops.

This changes how you work. On Junos you can make a sweeping change safely and review it before it exists. On IOS you make changes in an order chosen so that no intermediate state cuts your access.

Filtering vocabulary

Access lists, firewall filters and filter rules are the same concept. The important distinction is where they are applied and whether the default is permit or deny — and that default is the thing to check first on unfamiliar equipment, because getting it wrong is how you lock yourself out.

How to learn the next one

Do not start with syntax. Ask four questions: how do I see the running configuration, how do I see the routing table, how do I undo something, and what happens if I lose my session mid-change. Those four answers make you safe on any platform. The rest is reference material you can look up.