Can't PING - Please explain why

Deadmaster200

OK, guys, I just tried something real quick just to see if it would work.

I have a 2912 connected to a 2950 by a trunk link (fa0/10) using dot1q.

The 2950 is connected to e1 of a 2514 router through fa0/1.

I set the ip addresses of vlan1 on both switches so that it is in the same network as the ip address of the router's e0 interface.

e0 = 192.168.20.1
2950 vlan1 = 192.168.20.2
2912 vlan1 = 192.168.20.3

Of course, the default gateway is set to 192.168.20.1 on both switches.

I then created a vlan 20 name Test_20 on both switches.

I assigned port 1 on the 2950 to this vlan, which is the link to the router.

I assigned no ports on the 2912.

I can ping the router from 2950, but I can't from the 2912. Why not?
I unplugged the cable from port 1 and put on some other random port, and now I can ping the router from the 2912.

Again, why can't I ping from the 2912 when the 2950 is connected to the 2514 through port 1, which is assigned to a different vlan since there is a trunk link between the two switches?

Deadmaster200

OK, played around with a bit more.

The problem is not with the 2912 as I suspected. It must be something wrong with the VLAN, but I just don't understand why.

I cannot ping the 2514 from the 2950 despite that they are directly connected.

Yet, CDP packets are being exchanged as I can get the CDP info for the 2514.

I can't understand why I cannot ping the router just because I assigned that switch port to a different VLAN. Somebody please explain this to me.