Warning message

  • Cisco Support Forums is in Read Only mode while the site is being migrated.
  • Cisco Support Forums is in Read Only mode while the site is being migrated.

Share port between 2 VLANs

Unanswered Question
Nov 13th, 2001
User Badges:

I am thinking about seperation the switch into 2 VLANs, however there is only one ethernet port to connect between the switch and the router. So only 1 VLAN can have connection to the router (i.e, internet connection). What can I do to allow both VLANs to have internet connection? Please assist me


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
MickPhelps Tue, 11/13/2001 - 20:14
User Badges:

If both your router and switch support either 802.1q or ISL trunking, you can use a single switch port to the router for both vlans.


gpong Tue, 11/13/2001 - 21:12
User Badges:

Thanks for your reply. But can you say a little bit more into detail about how to do it?

From my knowledge we should seperate the ports into 2 groups, so vlan doesnt the port connected to the router belongs to?

MickPhelps Wed, 11/14/2001 - 05:59
User Badges:

I'd be happy to help, but I have no idea what hardware you're running.

If you configure the switch to trunk all of its vlans over a single port, and configure the router (if Cisco) with sub-interfaces using "encapsulation isl" or "dot1q", each sub-interface would be a logical interface to each vlan.


i-green Wed, 11/14/2001 - 06:18
User Badges:

could u list the commands to configure the subinterface on.. lets say.. an E0 port. Thanks

MickPhelps Wed, 11/14/2001 - 07:13
User Badges:

I believe you need to use FastEthernet to configure trunking support.

interface FastEthernet 0/0

no ip address


interface FastEthernet 0/0.1

encapsulation isl 1 (vlan 1)

ip address


interface FastEthernet 0/0.2

encapsulation isl 100 (vlan 100)

ip address


The "(vlan 1)" and "(vlan 100)" are not to be typed... just being clear. ;)


michaethompson Wed, 11/14/2001 - 13:28
User Badges:


If I remember correctly (I was only superficially involved) we had some problems when we wanted to do the exact same thing for our AAVID install at our office when we put in our IP PBX. When we attempted to configure the sub-interfaces on the ethernet interface, we had major issues with the data flow. We were forced to install a second interface to allow both voice and data to route via the 3640 we were using at the office.

I don't know that the issue has not been addressed, but this was as of 4 to 6 months ago.


srehan Wed, 11/14/2001 - 11:00
User Badges:

You need enable trunk in b/w switch and router with dot1Q or ISL encapsulation . Then you should be able to send 2 vlans across .


This Discussion