Inter VLAN routing with routed port

[sugatada9]

Folks,we know with native vlan and trunk port we can configure inter vlan routing with an external router. But how to configure inter vlan routing with a routed port? do we still need native vlan ip? what will be the draw back of using routed port?

[Waruna Wijewardena]

When you convert a physical port to routed port in L3 switch ,it act as router port , in this case you can't configure subinterfaces for vlans. So you will be ended up with connecting the switch to another L3 device on a router interface not a trunk interface. Inter vlans routing should be taken care of either one of L3 switch.

Hope I understand your question



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[Richard Burts · Accepted solution]

The original poster asks several questions. I suggest these answers:

- do we still need native vlan ip?

no you do not need the native vlan ip. and you can not have a native vlan ip if it is a routed port. As noted in the previous response there are no vlans associated with the interface when we make it a routed port.

- what will be the draw back of using routed port?

Let us think about an example using switch A connected to some other layer 3 device (perhaps a router or perhaps a layer 3 switch). If switch A configures its interface as a trunk and passes multiple vlans (including the native vlan) over the trunk, then the routing decisions are made on the other device and switch A can operate as a purely layer 2 switch. If switch A configured its interface as a routed port then switch A must operate as a layer 3 switch, and must have appropriate routing logic configured (perhaps static routes or perhaps a dynamic routing protocol) and switch A must make its own routing decisions. This makes the operation of switch A more complex. I am not sure if this is really a drawback, but it is one of the major implications of deciding to use a routed port.

HTH

Rick

[sugatada9]

Hi Waruna & Richard,

great! I understood your point. Now I am thinking about a very simple inter VLAN routing scenario. I have a L2 switch with few VLANs configured and then I want to connect this L2 switch to a router for inter VLAN routing. My questions are can I use a routed port in the L2 switch to onnect the router and configure inter VLAN routing from the router? Is it possible? If possible then what will be differences comparing to the typical configuration of connecting the L2 switch to router over trunk port with native VLAN?

[Richard Burts · Accepted solution]

Sometimes we need to be careful about terminology. When you describe your scenario you identify the switch as L2. If you really mean that it is a pure layer 2 switch then it can not do a routed port. A routed port is supported only on layer 3 switches.

In general if you want the routing to be done on the router then you should configure vlans and trunking from switch to router. If you want routing to be done on the switch then you could use routed port on the switch.

HTH

Rick

[sugatada9]

Hi Richard,
Great! Can you please describe how I can configure inter vlan routing in L3 switch with routed port. My another question is if i can configure a switch port as routed port with "no switchport" command & ip address, then why i can' t configure a routed port in L2 switch?


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[Richard Burts · Accepted solution]

How can I help you to understand that no switchport and ip address are layer 3 commands. And that by definition a layer 2 switch does not support layer 3 commands. (there is a minor exception to this to allow a layer 2 switch to configure an IP address for a management interface, but configuring an IP address on a physical interface is absolutely a layer 3 function and not supported on a layer 2 switch)

HTH

Rick

[sugatada9]

Hi Richards,

you are absolutely correct. I was confusing something. I can't use "no switchport" command or "IP address" command in L2 switch port. Hence Routed port is a L3 port and used in only L3 switch.

[Richard Burts]

I am glad that we got this settled. I understand your confusion when you thought that you remembered performing no switchport and ip address on a layer 2 switch port. But that is not supported. Thank you for using the rating system to mark this question as answered.

HTH

Rick