router-on-a-stick

[norberto_cammayo]

Hi,

Can anyone help me how to configure a router-on-a-stick? It would be very appriciated if explain as detailed. Tnx

[Roberto Salazar]

It's router with a single fastethernet connected to a switch and the router's interface is broken into sub-interfaces and encapsulated with either ISL or Dot1Q trunking, this is also called trunking so that the vlans can communicate via layer 3 - also known as inter-vlan routing, it's just routing, don't worry about the inter-vlan term if it will confuse the issue even more.

Here is a link with configuration example, sorry no pictures:

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800ca804.html#wp1003580

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[farkascsgy]

On the router do the following:

interface fastethernet0

interface fastethernet0.10

encapsulation dot1q 10 -> 10 identify VLAN10

interface fastethernet0.20

encapsulation dot1q 20 -> 20 identify VLAN20

I usually prefer dot1q encapsulation instead of ISL (if you want to use isl change dot1q to isl; but cisco 2950 only support dot1q I don't know what kind of device you have....). So you create subinterfaces with the proper encapsulation command. On the switch you should configure the uplink for trunk since you want transport more than one VLAN traffic over the uplink.

The id of subinterface is not significant, so it can be fastehernet0.21 for VLAN 20, but I prefer to use the VLAN id as subinterface id, anyway you will be confused.

Bye

FCS

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