Can one create a router-on-a-stick configuration without using vlans?

[jmaxwellUSAF]

Hi.

Instead of a

vlans with a router-on-a-stick

configuration, can one achieve the same connectivity result without vlans-- can one simply create on a

router port: sub-interfaces with ip-addresses in each subnet, and thus allow inter-subnet connectivity?

If not, why not?

Thank you.

[balaji.bandi]

How will they have communication if you do not have

vlan

tagging, how you identified where the packet from and where this need to go.

Other method you can do VRF ? (that totally different over engineering to solve simple solution).

[jmaxwellUSAF]

Thanks for the reply.

My thinking is that workstation GREEN from 10.0.1.0/24 connects to an L2 switch that connects to a router. Workstation RED from 10.0.2.0/24 connects to same switch. When each communication traverses from the switch to the router, because each

router sub-interface

is in a different subnet, it works.

Where is my understanding incorrect?

Thanks.

[MHM Cisco World]

SW-R 

Use one link for each

vlan

Here you dont need

subinterface

config in R

[balaji.bandi]

GREEN is Different broadcas domain and RED is different BROACAST domain in Layer 2 point of view.

To bridge between the Layer 2 domain, you need Router to route the the traffic in appropriate way.

 better explanation :  (dont want to invent wheel again)

https://www.ciscopress.com/articles/article.asp?p=2990405&seqNum=2

[jmaxwellUSAF]

This is not production question, this is theoretical question.

It's different L2 broadcast domain only if there are

vlans

. It is same L2 broadcast domain if there are no

vlans.

so as asked... 

Workstation GREEN from 10.0.1.0/24 connects to an L2 switch that connects to a router. Workstation RED from 10.0.2.0/24 connects to same switch. When each communication traverses from the switch to the router, because each

router sub-interface

is in a different subnet, it works.

Where is my understanding incorrect?

[Joseph W. Doherty · Accepted solution]

The problem you would have is the subinterfaces normally have some way to identify "their" traffic, such as a

VLAN tag, frame-relay DLCI, ATM PVC, etc.

You could, though, have different interfaces connect to the same L2 domain, each supporting a different network.

You could also have multiple networks on a single interface using secondary addressing but there are "issues" with the latter.