Question: Which two of the following statements described a routed switch port on a multilayer switch

[Steph1963]

Hi to Everybody,

I am trying to resolve the following questions:

Which two of the following statements describe a routed switch port on a multilayer switch (Choose two)

1) The routed switch ports supports VLAN subinterfaces

2) The port will not be associated with any VLAN

3) The routed switch port is used when a switch has only one port per VLAN subnet

4) Layer 2 switching and Layer 3 routing are mutually supported

5) The routed switch port ensures that STP remains in the forwarding state.

The answers are 2 & 3.

Can somebody explain me what really means ¨The routed switch port is used when a switch has only one port per VLAN subnet¨

I am not sure if this really make sense or not.

Thanks for your help

Stephane

[Giuseppe Larosa · Accepted solution]

Hello Stephane,

there was a thread some time ago about multilayer implementation in low end devices like a C3750 or likes.

A way to emulate a routed port is to have an SVI associated to a L2 Vlan with only one port associated with it.

In this way a cheaper ASIC can be used because routed ports are implemented using the same code for SVIs.

the price to pay in this type of implementation is that each routed port consumes one Vlan-id even if this vlan is not explicitly configured.

High end multilayer  switches have a different implementation and they do not consume one Vlan per routed port, they rather put all routed ports in a special Vlan ( 0 or 4094 first or last possible values in 802.1Q 12 bit wide Vlan space).)

Hope to help

Giuseppe

[mohammed hashim]

2) The port will not be associated with any VLAN

I realy can associate the port to a vlan and then give IP address to that port

(that will still make the port within the vlan

[Peter Paluch]

Hello Giuseppe,

You are probably referring to this thread:

https://supportforums.cisco.com/message/3847356#3847356

Thank you!

Best regards,

Peter

[andacn001]

The routed switch port is used when a switch has only one port per VLAN or subnet

Each routed port on a switch creates an internal VLAN for its use. These internal VLANs use extended-range VLAN numbers, and the internal VLAN ID cannot be used for an extended-range VLAN. If you try to create an extended-range VLAN with a VLAN ID that is already allocated as an internal VLAN, an error message is generated, and the command is rejected.

Internal VLAN IDs are in the lower part of the extended range. create extended-range VLANs beginning from the highest number (4094) and moving to the lowest (1006) to reduce the possibility of using an internal VLAN ID.

Before configuring extended-range VLANs, enter the show vlan internal usage privileged EXEC command to see which VLANs have been allocated as internal VLANs.

If necessary, you can shut down the routed port assigned to the internal VLAN, which frees up the internal VLAN, and then create the extended-range VLAN and re-enable the port, which then uses another VLAN as its internal VLAN. See the "Creating an Extended-Range VLAN with an Internal VLAN ID" section.

A routed Port is defined as follows

A routed port is a physical port that acts like a port on a router; it does not have to be connected to a router.
A routed port is not associated with a particular VLAN, as is an access port.
A routed port behaves like a regular router interface, except that it does not support VLAN subinterfaces.
Routed ports can be configured with a Layer 3 routing protocol.
Configure routed ports by putting the interface into Layer 3 mode with the no switchport interface configuration command.
Then assign an IP address to the port, enable routing, and assign routing protocol characteristics by using the ip routing and router protocol (eirgp, ospf, BGP, RIPv1/v2, ISIS...) global configuration commands.

switch virtual interface (SVI) is defined as follows

A switch virtual interface (SVI) represents a VLAN as one interface to the routing function.
Only one SVI can be associated with a VLAN (Only one VLAN is associated per SVI. A L3 switch can have multiple SVIs. For each Vlan one SVI).
Only when you wish to route between VLANs without a router on a stick configuration, you need to configure an SVI for a VLAN.
Configure a VLAN interface for each VLAN to route traffic, and assign it an IP address.
By default, an SVI is created for the default VLAN (VLAN 1) to permit remote switch administration.
An SVI does not become active until it is associated with a physical port (trunk or VLAN ID configured for an access port).
The VLAN corresponds to the VLAN tag associated with data frames on an ISL or IEEE 802.1Q encapsulated trunk or the VLAN ID configured for an access port.