Junior science refresher magazine

 Junior science refresher magazine

Junior science refresher magazine published this article page no 29 The configuration of the interface is where things get interesting.  Lets say we have two VLANs that will be using router-on-a-stick to communicate. Here is the VLAN information: VLAN 20:  20.20.20.0 /24 VLAN 40:  40.40.40.0 /24 The port on the switch that will be connected to the routers FastEthernet port must be in trunking mode and you must know the trunking protocol in use.  Well go with the Cisco-proprietary ISL here. The physical FE port on the router will not have an IP address.  The use of router-on-a-stick mandates the use of logical subinterfaces.  While we dont have to use the VLAN numbers for the subinterface numbers Ive found this helps you keep the interfaces straight.  One subinterface must be given an IP address in VLAN 20 and the other will have an IP address in VLAN 40. After creating subinterfaces fast 0.20 and fast 0.40 the config looks like this: interface fastethernet0 no ip address interface FastEthernet 0.20 ip address 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 youre almost done!  Now we need the encapsulation statement under each subinterface.  The subinterface statement must reflect both the VLAN number and the encapsulation type being used.  When were finished the config would look like this: interface fastethernet0 no ip address interface FastEthernet 0.20 ip address 20.20.20.1 255.255.255.0 encapsulation isl 20 interface FastEthernet 0.40 ip address 40.40.40.1  255.255.255.0 encapsulation isl 40 And thats it!  Your hosts in VLAN 20 should now be able to communicate with hosts in VLAN 40 and vice versa. A couple of final troubleshooting points - the most common error with router-on-a-stick is to put the wrong vlan number in the encapsulation statement.  Also make sure you have configured the routers IP address in VLAN 20 as the default gateway for hosts in VLAN 20 and do the same for VLAN 40. I hope youve enjoyed this look at router-on-a-stick.   While the name may get a chuckle out of you its still used in quite a few networks out there and knowing how to configure and troubleshoot it will get you that much closer to earning your CCNA and CCNP bright group of publications junior science refresher.

 Junior science refresher magazine