Communication of two different VLANs(Layer 2 switch) without the help of Layer 3 devices.

[YamanBelwal0505]

I have created two VLANs(as shown in images)respectively to two switches, Switch1 has VLAN 10 and Switch2 has VLAN 30,the switches are directly connected, my question is that how the two different VLAN's are communicating without the help of layer3 devices?(pinging images is also attached),so,if two different VLANs are communicating then why we use layer3 device?(when we do it straightway)

P.S. : 1.Normal layer2 switch(Manageable)

        2.The port which connects the two switches is not trunk.(hence,no trunking is done).

        3. I have given IP's as 192.168.1.1/24 and 192.168.1.2/24  (192.168.1.x /24)

also,what is the use of VLANs, if two different are communicating(like in terms of security {security flaws} ). 

Thanks in advance :)

[YamanBelwal0505]

Hi Sir @luis_cordova

I have one more question, then what us the use of this type of topology (Which I uploaded at first). Take an instance, in a company there is two departments namely, Sales and Engineering. Like sw1 has VLAN "Sales" and Sw2 has VLAN "Engineering", switches are connected, then it will share the information? Then what's the use?

Also, Is this a Bug? Or It happens for a reason?

Also, take another instance, sw1 has VLANs 10 and 20 and sw2 has VLANs 50 and 60 then, they will not share information(ignore trunking) even if they share same network/subnet whereas if, both switches has VLAN 10 in one and VLAN 20 in other, they will communicate.

(So, we conclude that if a switch has multiple VLANs, it will not communicate without trunking, although they are in same subnet/network) and if switches have only single VLAN they will communicate, then what's it use?

Thank You.! 

[luis_cordova · Accepted solution]

Hi @YamanBelwal0505 ,

I have one more question, then what us the use of this type of topology (Which I uploaded at first). Take an instance, in a company there is two departments namely, Sales and Engineering. Like sw1 has VLAN "Sales" and Sw2 has VLAN "Engineering", switches are connected, then it will share the information? Then what's the use?

Also, Is this a Bug? Or It happens for a reason?

If in your topology you have more than one vlan, the correct thing is to configure the links that connect the switches in trunk mode.
That prevents the packets from being re-tagged and achieves the purpose of the vlan, that is, that the packets are only retransmitted to the ports with the same vlan number configured.

Also, take another instance, sw1 has VLANs 10 and 20 and sw2 has VLANs 50 and 60 then, they will not share information(ignore trunking) even if they share same network/subnet whereas if, both switches has VLAN 10 in one and VLAN 20 in other, they will communicate.

I give you an example:

Switch1(vlan 10, 20, 30) <- trunk mode link -> Swtich2 (vlan 10, 40, 50)

In this topology, there will only be successful ping among the vlan10 PCs.

In order to have connectivity between PCs of different vlan, you will need a layer 3 device that does intervlan routing.

Regards

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