Passing Your CCNA and CCNP, and troubleshooting the configuration of the router on a stick

Passing Your CCNA and CCNP, and troubleshooting the configuration of the router on a stick For CCNA and CCNP candidates, it's hard not to laugh the first time you hear the phrase "router on a stick." Let's face it, is a rather ridiculous. But, as those who have passed the CCNA and CCNP exam knows, this is a topic of vital importance that the examination must know how to configure and troubleshoot. Cisco theory base for guests on different VLANs to communicate, a device-level 3 must be involved to address the routing between the VLANs. This device is a router, and there are special considerations that must be taken into consideration both the physical and the configuration of the router that you are writing. The router is connected to a switch via a FastEtheet port (or higher). The port of the router can not be an Etheet port, since the router port will need the ability to send and receive data simultaneously. The configuration of the interface is where things get interesting. Let's say we have two VLANs that will be used router on a stick to communicate. Here is the information VLAN: VLAN 20: 20.20.20.0 / 24 VLAN 40: 40.40.40.0 / 24 port switch to be connected to a router FastEtheet port must be in the process of connecting to the network, and it is necessary to know the trunking protocol in use . We're going to Cisco proprietary ISL here. The physical FE port on the router has no IP address. Using a router-on-a-stick mandates the use of logical subinterfaces. Even if you have not used the numbers VLAN subinterface numbers, I found it helps to keep the interface simple. One subinterface must be an IP address in VLAN 20, and both have an IP address in VLAN 40. After creating subinterfaces fast 0.20 and fast 0.40, the configuration is similar to this: not fastetheet0 interface IP interface FastEtheet 0.20 ip address 20.20.20.1 255.255.255.0 interface FastEtheet 0.40 ip address 40.40.40.1 255,255. 255.0 Believe it or not, it's almost done! Now we need the encapsulation statement for each subinterface. The subinterface statement must reflect both the number and type of VLAN encapsulation used. When ready, the configuration is as follows: the interface fastetheet0 no IP address interface FastEtheet 0.20 ip address 20.20.20.1 255.255.255.0 encapsulation isl 20 interface FastEtheet 0.40 ip address 40.40.40.1 255.255.255.0 encapsulation isl 40 That's it! Your hosts in VLAN 20 should now be able to communicate with guests in VLAN 40, and vice versa. A couple of points, the final resolution of the problems - the most common error with router-on-a-stick is wrong to put the number in vlan encapsulation statement. In addition, make sure you have configured the router's IP address in VLAN 20 as the default gateway for hosts in VLAN 20, and do the same for VLAN 40. I hope you enjoyed this look at the router on a stick. Although the name may get a laugh at you, is still used in some networks in the world, and how to configure and troubleshoot, it's closer than you ea your CCNA and CCNP.