Cisco CCNA 640-802 / CCENT Certification Exam Training :
Configuring "Router On A Stick"
By Chris Bryant, CCIE #12933
In your CCENT and CCNA studies, you quickly learn that hosts in different VLANs cannot send data to each other by default.
We have two options for configuring interVLAN communication:
L3 switches are becoming more and more prevalent in today's networks, and as a CCNA you should know that an L3 switch doesn't require an outside device to allow interVLAN communication. You're very likely to see ROAS configs on your CCNA exam, though, and let's face it - we can't just tear out a client's L2 switch and replace it with an L3 switch just because we want to!
We'll first go through an ROAS configuration with the following network, and then we'll take a detailed look at troubleshooting ROAS. Once ROAS is up and running, you can leave it alone for months or years, but there are quite a few ROAS details that we need to know to get it up and running!
Here's the network:
Right away, we've got a few important details to take note of:
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As expected, the switch ports connected to the hosts are access ports.
The switch port connected to the router must be trunking, and the trunking protocol (ISL or dot1q) on that port must be the same as that used by the router.
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The router must use a Fast Ethernet port for ROAS. A regular Ethernet port will not suffice. (Gigabit Ethernet, or 1000 MBPS Ethernet, is great, too, but you probably won't have a spare Gig Ethernet port to spare.)
Let's verify those VLAN memberships:
SW1#show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/3, Fa0/5, Fa0/6, Fa0/7
Fa0/8, Fa0/9, Fa0/10, Fa0/11
Fa0/12, Fa0/13, Fa0/14, Fa0/15
Fa0/16, Fa0/17, Gi0/2
2 VLAN0002 active Fa0/2
4 VLAN0004 active Fa0/4
Looks good. Since port Fa0/1 is trunking, we will not see it in that output; instead, we'll run show interface trunk.
SW1#show interface trunk
Port Mode Encapsulation Status Native vlan
Fa0/1 on isl trunking 1
That port is up and trunking with ISL encapsulation. We'll begin the router configuration in next installment of my exclusive Cisco CCENT / CCNA certification exam tutorial series!
Five Minutes From Now, You Can Be Studying For CCNA Exam Success Just As Thousands Of Other CCNA Candidates Around The World Have - With Chris Bryant, CCIE #12933 With You Every Step Of The Way - With The Ultimate CCNA Exam Study Package!
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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