difference between overlay and vlan transport zone

[MustafaSadek]

hello friends. iam new to NSX-T and i have misunderstand or confusion between the  use case of overlay and Vlan TZ

correct that if iam mistaken:

i  understand that we need the Overlay tz to forwarded geneve traffic between hosts, and i know that TEPs make the tagging for the vlan and add the header of vlans (vni ) to their frames while they go out to the underlay network(the physical) when they connect with each others

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question here : if we used VLan transport zone,, and the vlan wants to connect to other vlan in other host , then it will have to go through tep too and get vni and will go through geneve traffic cycle ( same like Overlay TZ) ?? 

what is difference here and what i misunderstand ?

Thank you all 

[shank89]

Think of a VLAN TZ and the subsequent VLAN backed segments the same as a VDS portgroup.  

What that means is, they are just tagged portgroups that utilize the physical network gateways to route traffic.  They do not utilize GENEVE tunnels, TEPs or any form of logical routing.  Those are benefits of Overlay networks.

[MustafaSadek]

Dear shank, 

Thanks for your reply . 

you mean that in vlan transport zone , the Vlans can't be tagged through the geneve , they will have to be tagged on physical network to communicate with each others? and if yes , still have confusion , what is the benefit of this , while we can use geneve tunnel ?

sorry still can't understand or have something i mess in my networking background knowledge, and i appreciate you clarify more  

[shank89]

The concept of VLANs do not exist with overlay segments, they have VNI (virtual network identifiers).  The only VLAN used with overlay / GENEVE are the transport VLANs between host TEPs and Edge TEPs.

Some circumstances call for VLANs to remain, its generally a decision on a case by case basis.