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romanroma
Beginner

Router interface+Layer2 links vs SVI+vlan when trying to extend connection

I need to extend Layer 1 over to a demarc junction; however, I do not have the capability to run a dedicated Layer 1 path. Due to the latter, I know SVI on my Core will work, via vlans; however, would there be any benefit to create a 'router' interface on my L3-Switch and just carve up 2-ports on my switch to extend that link over to my demarc. I hope the picture explains the idea better.

 

From what I understand - the SVI still has the switching overhead (stp, bpdu, etc); however, do I still have this overhead if I have to pass the path through a layer 2 switch?

topology.jpg

This will still be a /30 on the SVI or Router interface, but which way of deployment makes more sense when I need traditional routing with possibly(not sure yet) OSPF or EIGRP applied.

 

Thank you

RR

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I am not clear what commands are not supported on SVI that you would need to do routing. Can you provide some clarification on this?

And I do not understand the comment about layer 3 link providing more control. Both suggested methods (routed interface or SVI) are providing a layer 3 link and I do not see where there would be any difference in control.

My first observation is that if the interface is configured as a routed interface then it will not expect to process BPDUs. But since it will be connected to an access port in vlan 100 the routed interface will receive BPDUs. For consistency I would prefer the approach of using an access port in vlan 100 with an SVI.

My second observation is that to a very small degree the approach of a routed port does simplify the configuration. With a routed port all of the configuration is on a single port and there is no need to configure vlan 100 or an access port in vlan 100 or an SVI for vlan 100.

I believe that either approach can work and that the differences in approach are relatively minor. So no clear advantage for either method.

I do find the original post a bit confusing. It starts by saying "I need to extend Layer 1 over to a demarc junction". But then it suggests approaches that use a layer 3 link. Perhaps we need a better understanding of that environment and of what the requirements really are.

 

HTH

Rick

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6 REPLIES 6
MHM Cisco World
Collaborator

I think they work same but some command not support under SVI so you need L3 interface.

balaji.bandi
VIP Master

if you do not need layer 2 extension towards DMZ (demarc junction;)  - then I prefer the Layer 3 link.So you have control over routing.

(hope I have understood the requirement correctly here).

BB

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I am not clear what commands are not supported on SVI that you would need to do routing. Can you provide some clarification on this?

And I do not understand the comment about layer 3 link providing more control. Both suggested methods (routed interface or SVI) are providing a layer 3 link and I do not see where there would be any difference in control.

My first observation is that if the interface is configured as a routed interface then it will not expect to process BPDUs. But since it will be connected to an access port in vlan 100 the routed interface will receive BPDUs. For consistency I would prefer the approach of using an access port in vlan 100 with an SVI.

My second observation is that to a very small degree the approach of a routed port does simplify the configuration. With a routed port all of the configuration is on a single port and there is no need to configure vlan 100 or an access port in vlan 100 or an SVI for vlan 100.

I believe that either approach can work and that the differences in approach are relatively minor. So no clear advantage for either method.

I do find the original post a bit confusing. It starts by saying "I need to extend Layer 1 over to a demarc junction". But then it suggests approaches that use a layer 3 link. Perhaps we need a better understanding of that environment and of what the requirements really are.

 

HTH

Rick

View solution in original post

romanroma
Beginner

I needed to extend a physical cable beyond the location of the layer3 switch, so a switch is in the middle. Due to the latter, was not sure if I should make a 'routed' interface or a SVI to have the logical path and in this case the physical path trace through a switch.

 

Hello,

 

so you are still looking for help with this ? Or has this issue been resolved ?

@Georg Pauwen 

I think I have made up my mind for what I want to do. I am not sure if I need help, since it looks like it is a 50/50 split on method and how to deploy. I just wanted to update the ticket with the best example and more detail, so future folks can learn if they found my post.

 

Thank you.