Native Vlans Help

can anyone really help me out with a good explanation of cisco native vlans. I know its for untagged frames but how does a native vlan function on a router's subinterface when you put

encapsulation dot1q 99

and

encapsulation dot1q 99 native.

Whats the different ?

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Comments

wastedtime

The difference is "encapsulation dot1q 99" will add the 802.1q vlan tag on a trunk for vlan 99. When you add the word "native" onto it, it will keep that vlan untagged over a trunk. Native just means that it won't tag the vlan. By default the native vlan is 1.

Darian929

My real question is as I was talking to one of my co-workers also, for the CCNA they teach you native vlan's but its truly not used for the labs or anything in the sens that the frames are always tagged and we don't to like voip setups, where native vlans are truly needed. So that's why I guess I dont get the whole point of native vlans on trunk links.

tha_dub

Trunk links pass native vlan frames the same as non native. The only difference is that the native vlan frames are not tagged. In essence the lack of a tag is the tag or vlan identifier to the switches.

Where you have to be careful is if you program the native vlan to anything other than 1 which is the default. If you do this you must program it the same on all other switches in the LAN and the ROAS. If you don't the VLAN's will bleed across each other which could really mess with your network.

thenjduke

Pretty much what everyone else has said. You would usually use native vlans for voip setup these days but the days when hubs were around and you had a bunch of people plugges into a hub and the hub into the switch you would usually do native vlan like that.

Darian929

hey guys thanks, so basically dont mess with native vlan's on trunk links and just leave it to its default of vlan 1, and If i do change it make sure to change it onto all of the switches and routers sub interface to the same native vlan. got that, I just didn't want to bog myself down to much on that when that is not really used to much for now atleast on CCNA even though I do understand the concept a bit.

Netwurk

Hi Darian929

The commands you referenced in your first post are router commands. To understand dot1q and native VLANs (and also tagging), it would be better to look at it from a switching perspective. For a switch, the commands involved are:

switchport trunk encapsulation dot1q
switchport trunk native vlan #

Just wanted to point that out, the other posts cover the basics

krisfday

I have one question about tagging. At what step, or by which device is the "tagging" being done?

Zartanasaurus

krisfday wrote: »

I have one question about tagging. At what step, or by which device is the "tagging" being done?

By the switch if it has to send a frame over a trunk link. A trunk can support multiple VLANs, so a tag is inserted to identify the VLAN the frame belongs to.

networker050184

krisfday wrote: »

I have one question about tagging. At what step, or by which device is the "tagging" being done?

Depends on the setup. 802.1q tags are only present on 802.1q trunk links so which ever device is sending the frame over a trunk needs to tag it.