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VLAN routing? Do I need to?

I have an application, and I am wondering if I can or need to route VLANS.


I have a Main Site and a Remote Site. I have CISCO 2620 Routers at both ends of a Point to Point T1 link. Both routers's Fa0 ports are plugged into CISCO 2950 switches.


I have a group of devices at either end that need to communicate to each other with high priority and need to be isolated. Each group of devices at either end have their own subnet, and their own VLAN. The subnet routing is handled by secondary IP addresses on each router's Fa/0 port.


The switch ports going to the routers are programed as VLAN trunks, and the switch ports for the End Devices are programmed as VLAN2 only, static access (?).


Question 1) I believe that I need to have 801.2q available on the routers to allow the traffic to remain 'isolated' on the appropriate VLAN when it gets to the far end. Do I? If so, do I need to build subinterfaces (assign IP addresses, apply 802.1q encapsulation, and add an appropriate VLAN IDs) on the Fa/0 ports on each router? Do I then make the Gateway of these devices be the far end's subinterface? Or, do I need to have seperate physical ports on the router?


Question 2) Eventually, On one end, the devices will be set up to send frames either "untagged" or tagged with VLAN2. I understand that the cooresponding switch ports will then need to be changed to trunk ports with the native VLAN being 1. What would happen if a device is programmed to send out information with VLAN2 tags, but the port is already set to VLAN2 static access? Is it double-tagged? :)


When I leave everything in VLAN 1, I can ping across from end-to-end no problem. So my overall routing seems to be okey.

  • Other Network Infrastructure Subjects
Cisco Employee

Re: VLAN routing? Do I need to?

1) if you want to separate two networks under same interfaces then trunking is your options and yes, you have to do subinterfaces and make sure switch port is configured for trunking and all the ports to the right vlans using the switchport access vlan # commands.

You can do the same thing with two physical interface on the router if you think one interface will not be enough to carry all the traffic and in that case, every port will be different vlan on the switch.

2)When the access ports configured with some vlan, when the traffic is coming into those ports are coming without tagged- Packets will tagged only when it is going over the trunk port which mean one physical ports carrying all the traffic so they have to tag itl.

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