Clarification on VLANing

Unanswered Question
Mar 3rd, 2008

I have an issue with VLANing. I have everything configured properly on 8 switches and a router. This is a router-on-a stick design. I am planning on using 5 3560 Cat switches with VLAN 54(default gateway VLAN1 and 3 3560 Cat switches with VLAN 51(default gateway VLAN1 All switches have the trunk ports with dot1q configured properly as well as the subinterfaces on the router.

My questions:

When I assign an Ip address to a client that is plugged into one of the swiches that have VLAN54 and try to ping the switch or router, the ping fails. The same is true when I try to ping the client from the switch or the router. What seems to be the problem ?

2- When should I configure a native dot1q on the router? Is it required when configuring a router-on-a-stick?

Attached is the output from the router and one of the switches.

I have this problem too.
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lamav Mon, 03/03/2008 - 11:16

"2- When should I configure a native dot1q on the router? Is it required when configuring a router-on-a-stick?"


Here is a sample router-on-a-stick configuration:

Switch Config:

vlan 100


vlan 200


interface fastethernet 1/0/1

description To_router_fa0/0


switchport trunk encapsulation dot1q

switchport mode trunk

Router config:

interface fastethernet 0/0

description To_L2_Switch_fa1/0/1

no ip address

interface fastethernet 0/0.1

encapsulation dot1q 1 native

interface fastethernet 0/0.100

encapsulation dot1q 100

ip address

interface fastethernet 0/0.200

encapsulation dot1q 200

ip address


Please rate this post if it does.


Jon Marshall Mon, 03/03/2008 - 11:19


You don't need to configure a native vlan on the router. I would take off the native tag and then try to ping from a PC in vlan 54.


skhirbash Mon, 03/03/2008 - 14:25

I was able to ping from a PC to a router and vice versa. The router's port is plugged into the same switch(SW1) as the PC and this switch (SW1)is configured with VLAN54. However, the PC that is connected to other switch(SW2), which is configured with VLAN 51 and has a trunk port connected to SW1, is unable to ping the router and the router isn't able to ping this PC. I spent almost half a day trying to figure out why this is happening but couldn't. Any assistance will be appreciated!!



lamav Mon, 03/03/2008 - 14:33

Perhaps it's time you posted the full configs of the router and switches 1 and 2.

If you're trunking switch 2 (vlan 51) to switch 1 (vlan 54), where switch 1 is acting as a pass-through for vlan 51, I'm wondering if you have to configure vlan 51 on switch 1...

skhirbash Mon, 03/03/2008 - 14:51

Thank you Jon!! You did enlighten me on creating VLAN51 on SW1 and that did the trick. I acutally configured SW2 with the same VTP domain and gave it a server mode where the same VLANs were replicated to both switches.

Thanks for your efforts!!


lamav Mon, 03/03/2008 - 15:00

Hey, SK:

Im glad it worked for ya!

Please feel free to rate my posts so that I can collect my brownie points. ;-)


skhirbash Mon, 03/03/2008 - 15:01

Sorry about that!! Thank you Victor and thanks to you Jon as well for the effort.



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