VLAN information

Hello - I'm just trying to figure out this problem in my head so here is the situation

Suppose you have (1) router sonicwall/cisco - 1 director class switch (hp/cisco) and a bunch of workstations.

If I assign three separate VLAN's and sub-interfaces on the router, are the workstations in each separate VLAN able to communicate with each other if the workstation's NIC do not support VLAN tagging/trunking (hp/cisco)

From what I gather the switch port's define what vlan membership but get stripped the vlan tag information if the workstation's NIC does not have 802.1q enabled/available.

Sorry if this is in the wrong section, or sounds confusing!

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billscott92787

fluk3d wrote: »

Hello - I'm just trying to figure out this problem in my head so here is the situation

Suppose you have (1) router sonicwall/cisco - 1 director class switch (hp/cisco) and a bunch of workstations.

If I assign three separate VLAN's and sub-interfaces on the router, are the workstations in each separate VLAN able to communicate with each other if the workstation's NIC do not support VLAN tagging/trunking (hp/cisco)

From what I gather the switch port's define what vlan membership but get stripped the vlan tag information if the workstation's NIC does not have 802.1q enabled/available.

Sorry if this is in the wrong section!

When you assign the router sub interfaces, you define the different VLANs in which they are in when setting these up, using the encapsulation dot1q # command. This allows the PDU to pass up to the router, and be re-encapsulated with the proper VLAN tag information, then it is sent back out that interface toward the destination VLAN. When it makes it to the switch that has the node connected to it, it removes that tag and forwards it out the interface. Someone please correct me if I am wrong.

fluk3d

That sounds about right, I wasn't sure tho and wanted to double check. Most of the workstations I'm working with do not have NIC's that support 802.1q so I thought I would ask

ConstantlyLearning

fluk3d wrote: »

That sounds about right, I wasn't sure tho and wanted to double check. Most of the workstations I'm working with do not have NIC's that support 802.1q so I thought I would ask

Why do you think an end host needs to support 802.1q?

fluk3d

ConstantlyLearning wrote: »

Why do you think an end host needs to support 802.1q?

I was under the impression it would be able to communicate with other vlans without the use of the router if I was using a L3 switch however that wouldn't make sense...

Forsaken_GA

ConstantlyLearning wrote: »

Why do you think an end host needs to support 802.1q?

Sometimes it does. Servers which support trunking can be very useful in some situations

Forsaken_GA

fluk3d wrote: »

I was under the impression it would be able to communicate with other vlans without the use of the router if I was using a L3 switch however that wouldn't make sense...

Why doesn't that make sense? A layer 3 switch is, essentially, a switch with routing capabilities. A layer 3 switch will allow you to do intervlan routing without the need for a router on a stick.

In a nutshell, your end hosts are ignorant of vlans. The only time you need 802.1q trunking support is when a link is going to carry information for more than 1 vlan, ie, switch to router connections, or switch to switch connections.

If your switch is layer 2 and you're using a single link to the router, then the link to the router would be a trunk. You'd setup your subinterfaces to act as the gateways for the individual vlans, and the only thing that needs to support dot1q is the switch interface connection to the router, and the routers interface to the switch. Say you have a host in vlan3 that wants to talk to a host on vlan1. The host sends it to the switch, the switch sends it up the trunk to the router, the router looks at the tag to see which vlan the traffic is for and delivers it to the vlan3 subinterface gateway. Then normal routing is performed, the router sees it's destined for vlan1, sends it back down the trunk to the switch, this time tagged for vlan1, and the switch delivers it to the end node.

If you have a layer 3 switch, this is all irrelevant, in the same situation, you'd have an SVI setup as the gateway for vlan3, and an SVI setup as the gateway for vlan1. The host on vlan3 would send the packet destined for vlan1 up to the switches vlan3 SVI, which would then route it to the vlan1 SVI, which would then put it down the appropriate wire for delivery to the host. No frame tagging is involved.