VLAN help

Mar 21, 2006 1 Replies
VLAN help open original image

Hi there,



I'm studying for my CCNA and am messing around with a few different VLAN scenarios.


Up until now, we have been taught to use different subnets for each vlan.


e.g. VLAN2 > 192.168.2.x VLAN3 > 192.168.3.x


However, I would like to see what happens when you have different VLAN's on the same subnet.


So, I've got two hosts;


Host A is on VLAN 2 and has an IP address 192.168.4.3/24 Host B is on VLAN 3 and has an IP address 192.168.4.20/24


I've configured the ports on the 2950 to enable static VLAN's for the two ports. Up until now, there is no problem...Host A can ping other hosts that have been assigned onto VLAN 2 and Host B can ping other hosts on VLAN 3. Neither can ping each other.


But, I'd like to configure inter-VLAN routing. Is this not possible because they are on the same subnet?


I've connected and configured a trunk link between the 2950 switch and a 2600 router, and set;


2600(config)# interface f0/1
2600(config-if)# no ip address
2600(config)# no shut
2600(config)# interface f0/1.2
2600(config-subif)# encapsulation dot1q 2
2600(config-subif)# ip address 192.168.4.1 255.255.255.0
2600(config-subif)# exit
2600(config)# interface f0/1.3
2600(config-subif)# encap dot1q 3
2600(config-subif)# ip address 192.168.4.19 255.255.255.0


However, Host A can ping both 192.168.4.1 and .4.10, whereas Host B can



ping neither addresses.


Is it not possible to enable inter-vlan routing this way, or am I doing



something wrong? I assume the problem is because you are assigning two subinterfaces on the same subnet on the router, but I thought that with



the dot1q x command you were speciyfing that only VLAN x could communicate with it?


Would appreciate an explanation!


Thanks, Dilan



take a look at

Understanding and Configuring VLAN Routing and Bridging on a Router Using the IRB Feature

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