Sunday, April 4, 2010


At this point we would have all switch ports in VLAN 1. Now, we'll create three extra VLANs which are:10 - Sales
20 - Marketing
30 - Engineering

To do this, go into VLAN database and type:
vlan 10 name SALES
vlan 20 name MARKETING
vlan 30 name ENGINEERING

Now, suppose we want to change Host A into VLAN 10 and Host B into VLAN 20. To do this, go under S2 and type:
in f0/8
sw a v 10

Then go under S3 and type:
in f0/8
sw a v 20

Now, suppose that VLAN 10 would be 192.169.10.x/24 and VLAN 20 would be 192.169.20.x/24. We would have Host A and Host B as the .20 of each of their subnets.

Now, for Host A to ping Host B, you'll need some sort of routing between the VLANs. This would require you to turn one of your routers into a Router-On-A-Stick. We would choose R1 as the Router-On-A-Stick. To configure it, we need to create subinterfaces like this:
in f0/1
no ip add
in f0/0.1
encap dot 1
ip add
in f0/1.10
encap dot 10
ip add
in f0/1.20
encap dot 20
ip add
in f0/1.30
encap dot 30
ip add

You'll now also need to add the subnets into the RIP process for R2 and R3 to reach the VLANs:
router rip

Normally on an Ethernet network, the largest packet you can send is 1500B. Adding a dot1q tag onto an Ethernet frame would result in a 1504B frame. This is known as a baby giant frame. Cisco automatically adjusts the MTU down to 1496, which allows the 4 byte tag to make a packet 1500B.

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