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Driving Your CCNA and CCNP: Configuring And Troubleshooting Router-On-A-Stick

For CCNA and CCNP prospects, it's difficult not to laugh initially you hear the expression "router on a stick." Let's face it, that's a pretty ridiculous term. But as those who have passed the CCNA and CCNP exams know, this can be a essential test matter that you must know how to manage and troubleshoot. Simple Cisco principle states that for hosts in various VLANs to talk, a Layer 3 device must be involved to handle the routing between the VLANs. That product is just a router, and there are special factors that should be taken into account for both the real router it self and the setting you'll be writing. The router will soon be connected to a change via a FastEthernet port (or better). The router port can not be a typical Ethernet port, because the router port will need the ability to receive and send information at the same time. Where things get interesting the configuration of the program is. Let us say we have two VLANs which will be using router-on-a-stick to communicate. This can be a VLAN information: VLAN 20: 20.20.20.0 /24 VLAN 40: 40.40.40.0 /24 The port on the move that will be attached to the router's FastEthernet port must be in trunking setting, and you must know the trunking method being used. We'll opt for the Cisco-proprietary ISL here. The actual FE port on the switch will not have an internet protocol address. The use of router-on-a-stick mandates the use of rational subinterfaces. I have found this can help you keep carefully the interfaces directly, while we don't have to make use of the VLAN numbers for the subinterface numbers. One subinterface should be granted an address in VLAN 20, and another will have an address in VLAN 40. After producing subinterfaces fast 0.20 and fast 0.40, the config seems like this: Screen fastethernet0 Number internet protocol address Software FastEthernet 0.20 Ip 20.20.20.1 255.255.255.0 interface FastEthernet 0.40 ip address 40.40.40.1 255.255.255.0 Believe it or not, you're nearly done! Now we are in need of the encapsulation statement under each subinterface. The subinterface record must reflect the VLAN range and the encapsulation type getting used. When we are finished, the config would look like this: Software fastethernet0 no ip Screen FastEthernet 0.20 Ip 20.20.20.1 255.255.255.0 encapsulation isl 20 interface FastEthernet 0.40 Ip 40.40.40.1 255.255.255.0 encapsulation isl 40 And that is it! Your hosts in VLAN 20 must now be able to talk to hosts in VLAN 40, and vice versa. A couple of final troubleshooting details - the most typical mistake with router-on-a-stick is to put the wrong vlan number in the encapsulation statement. Also, be sure you have configured the router's IP address in VLAN 20 while the default gateway for hosts in VLAN 20, and do exactly the same for VLAN 40. I hope you have enjoyed this look at router-on-a-stick. It's still utilized in quite a few sites out there, while the name may get a out of you, and focusing on how to manage and troubleshoot it'll get you that much closer to making your CCNA and CCNP. guide to cnc router