VLAN related question

[Sagar4]

If trunk port can be created between two layer 2 switches, then why we need a layer 3 device to allow communication between different vlan users?

[balaji.bandi · Accepted solution]

 why we need a layer 3 device to allow communication between different vlan users?

Trunk allowed VLAN to stretch the L2 broadcast domain to other switches, this not have ability to routing between VLAN

yes, you're required only in the same VLAN example VLAN 10 only needs to interact with VLAN 10  in the same broadcast domain as the host then you do not need it.

If you looking to establish other vlan examples VLAN 20, that is where you need a Layer3 interface to route between VLAN 1- and VLAN 20 using  Routing tables.

[Sagar4]

So what I have understood is destination ip address of sent data won't be checked until it reaches layer 3 device because layer 2 device only look for mac addresses.

[Richard Burts]

Yes. Your understanding is correct - and you have stated it very well (the detail that the IP address is layer 3 data and is not considered by layer 2 devices is something that BB and I have in mind but did not state).  Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information.

[balaji.bandi]

yes correct - The layer 2 domain does not resolve other Layer 2 domain, so it required to Layer 3 interface to route between

there are many content videos available on how that works, check in you Tube.

Good course CCNA :

https://www.youtube.com/watch?v=H8W9oMNSuwo&list=PLxbwE86jKRgMpuZuLBivzlM8s2Dk5lXBQ

[Joseph W. Doherty]

Not exactly.  Two hosts within the same L2 domain (like a VLAN) still (usually) communicate using L3 and higher levels.  In fact, at L3, a host doesn't usually care or directly know or logically work differently depending on whether other host is within the same L2 domain or not.  Also, the same L2 domain can host multiple L3 networks.

To put it another way, you need L3 to jump across L2 domains, but you don't need multiple L2 domains to have multiple L3 networks.

[Richard Burts]

I agree with BB that if 2 switches are connected using a trunk port that any device in vlan 10 of one switch can communicate with devices in vlan 10 of the other switch (and vlan 20 devices can communicate with vlan 20 devices of the other switch). But if a device in vlan 10 wants to communicate with a device in vlan 20 (on same switch or on other switch) then you need a layer 3 device (router or layer 3 switch) to enable the communication.