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.

EdTheLad

You have assigned the port on the 2950 thats connects to the router to vlan 20.This means if you want to communicate with this port via ip, you need to set the ip address on the vlan 20's interface.
Alternatively you could set the port to be a trunk and setup dot1q encapsulation on a subinterface on the router.

Deadmaster200

Can't set it as a trunk as its a: a 2500 series and b: a 10m interface.

When you say set the ip address of the vlan interface itself, you mean in the same way that we set the vlan1 interface for administration? COOL! thanks.

NetworkGod

i didn't know CDP 'exchanges packets'