VLANs

[Need Not To Know]

Can these two PCs ping each other without a Router On A Stick?

[MHM Cisco World]

No you can not.

Since each one have different subnet you need l3 device to interconnect these PC

MHM

[Need Not To Know]

1- thank you

2- can I put them in same subnet but with same topology in the picture?

3- what about this topology, same thing? I can't ping between two PCs until I use ROAS?

[MHM Cisco World]

1- thank you

You are welcome 

2- can I put them in same subnet but with same topology in the picture? NO since there is router between two them you need to use different subnet

3- what about this topology, same thing? I can't ping between two PCs until I use ROAS?

If the SW to router config as trunk then you need ROAS 

If the Saw to router link config as access (switchport access vlan x) then no need ROAS

MHM

[Need Not To Know]

1- thank you so much, I am Sorry for bothering you

2- about the previous point (3), this example is easier but I can't do ping between two PCs

note that this is the configuration, and there is no configuration in the router

[MHM Cisco World]

I make second review' config is correct no need anything except you need to specify GW in both PC.

Do you use subinterface in router?

MHM

[Need Not To Know]

1- so I can't configure just one VLAN, right?

2- my point was it's like I have a main branch where I have the Router

then other two branches, each one have a Switch

and i want to connect between two branches(switches)

in this scenario, I should use ROAS, right?

3- thank you really

[MHM Cisco World]

Let make some rules here 

1- unique subnet per all your topolgy 

2- ROAS use only IF the SW connect to router via trunk.

2 - unique vlan per one router use RoAS

MHM

[M02@rt37]

Hello @Need Not To Know 

VLAN are locally significant. You could have vlan id 2500 on two sites but you can not have same subnet separated by Routers. By definition Routers route network. You should have different subnet on the 2 sites. Each router performing routing protocols in order to reach site's subnet.

[MHM Cisco World]

Vlan locally if he dont use subinterface (ROAS) if he use it 

The  it effect router.

The router dont know how routing traffic between two subinterface in two mean interface using same vlan tag.

This make traffic disruption.

MHM

[Need Not To Know]

@MHM Cisco World 

M02@rt37 

I'm really thankful for you 

[M02@rt37]

You're so welcome @Need Not To Know 

[Joseph W. Doherty]

Your attachment shows two routers, so if you have 3 subnets and routers know remote subnet and PCs have correct gateway, etc., what you've posted should work fine.  Unclear why you mention a ROAS.