Vlans and unmanaged switches

[sawquecisco]

Hi

I have read a lot of things about vlans and the explanations that I found on the internet makes me confused.

1-) A Vlan can be implemented without trunking. Right?

2-) Does unmanaged switch support vlan without trunking?

3-) Does unmanaged switch support vlan with trunking?

I am trying to understand whether unmanaged switches have problems with vlans or just truning feature of vlan or both of them???

Thanks...

[John Blakley]

1-) A Vlan can be implemented without trunking. Right?

A vlan can be on a trunk or a standard access port.

2-) Does unmanaged switch support vlan without trunking?

Unmanaged switches are unmanaged, so they are just dumb switches

3-) Does unmanaged switch support vlan with trunking?

See 2...

You'll need a managed switch to do anything with Vlans...

Please rate helpful posts...

[hobbe]

Hi

This is my view on the subject.

1) yes today basically all switches are using vlans. You can fx use one switch and have several vlans in that switch alone wich means that you would not need to make a trunk since all of the ports would be access.

Trunks is only the possibility to send several different vlans over the same line.

the opposite of a trunk is access (if spoken in the language of cisco)

trunk = possibility of several vlans

access = possibility of one vlan and thus it needs no tagging.

2) I would say that i do not know of a unmanaged switch that supports vlans per se.

but if you only set the unmanaged switch up with an access port, the unmanaged switch will not know the difference if it is a vlan or not.

so yes that would work but it would from the perspective of the unmanaged switch not be vlans.

3) I would state that no this would not work since the unmanaged switch would have no idea if the port was a trunk port with many or a few vlans on it or an access port with just one vlan that does not have taggs on it.

simply put the unmanaged switch would not be able to know what vlans it would or would not send over the link that might or might not be a trunk. neither will it have knowledge of what vlan is the native (the only one on the trunk that is not tagged) vlan. so what would happen if one put it in on a trunk ? well in my mind either the native vlan would work and the switch would throw away all the others, or the unmanaged switch will drop all. but we do not know wich since there are many different unmanaged switches and atleast some of them would behave differently.

so for these reasons i do not think there is a unmanaged switch that works with Vlans, but i know that they work with ports that are access ports only towards switches that are using vlans. 

Good luck

HTH

[Joseph W. Doherty · Accepted solution]

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Posting

# 1, yes with the most common configuration being assigning individual ports to individual VLANs, although some switches support other kinds of VLANs too; some switches even support protocol based VLANs.

# 2 and 3, no for both, as non-managed switches don't have a way to define or manage VLANs nor do they support VLAN frame tagging for trunk support.  (Trunks extend the original frame with a VLAN tag prefix.  This is what allows a switch, that also supports VLANs, to recognized what VLAN a particular frame is part of coming from another switch when VLANs share a common link.  Without trunk support, you can extend VLANs between VLAN capable switches, but you would need to dedicate a port on both switches for each VLAN you want to extend.)

I am trying to understand whether unmanaged switches have problems with vlans or just truning feature of vlan or both of them???

An unmanaged switch can't support VLANs (again because there's no way to define or manage them).  A managed switch doesn't have to support VLANs nor does a managed switch that supports VLANs need to support VLAN trunks, although you wouldn't have a switch support VLAN trunks that doesn't also support VLANs.  NB: Today, any managed switch is likely to support both VLANs and VLAN trunks.