[Kea-users] KEA DHCP and VLANS...

Talkabout talk.about at gmx.de
Sun Feb 2 21:02:09 UTC 2020

Hi Tom,

let me get this straight:

1. Create VLAN on switch (vlan20)
2. Create VLAN 20 interface on dhcp server and move the physical address to the new interface
3. Bridge native VLAN port on swtich to VLAN 20 port on switch

The result should be that the dhcp Server gets all packages in VLAN 20. What I am a Little bit confused About is why the „bridging“ causes the packets to arrive as vlan20 tag. Is it because the switch sends received packets on the untagged port, receives them on the tagged port and Forwards them (tagged) again to all ports that are members of the tag? In such a case what I also Need to do is to make sure that the port, where the dhcp Server is connected, is a tagged member of VLAN 1, correct?

What are the disadvantages of this „hack“? It seems to me that the Network traffic increases. Basically traffic that was send previously only to untagged ports now will also find its way to all ports tagged with VLAN 1. Is this all or do I have to expect other issues?


Gesendet von Mail für Windows 10

Von: Dajka Tamás
Gesendet: Sonntag, 2. Februar 2020 21:14
An: 'Talkabout'; 'Oehlrich, Benedikt'
Cc: kea-users at lists.isc.org
Betreff: RE: [Kea-users] KEA DHCP and VLANS...


that’s why I’ve written the dirty workaround. Since you’ve only trouble with the native vlan, than a possible solution is to ’tag’ the native vlan with a crosslink on the swicht (looping back to itself). This way you can tag the native vlan transparently.

So you create a new vlan – vlan 20 let’s say – remove the ip from the pysical interface and assign it to interface vlan20. On the switch you cross connect a native vlan port with a vlan 20 access port „bridgeing”  it together (all packets in the native vlan will appear to KEA as vlan 20 packets).

With openvswitch you’ll to nearly the same, but virtually. If openvswitch honors the tagged/untagged scenario correctly, than it’ll work.



From: Kea-users [mailto:kea-users-bounces at lists.isc.org] On Behalf Of Talkabout
Sent: Sunday, February 2, 2020 7:42 PM
To: Oehlrich, Benedikt <boe at codemanufaktur.com>
Cc: kea-users at lists.isc.org
Subject: Re: [Kea-users] KEA DHCP and VLANS...

Hi Ben,

in my case I think the prerequisite is a Little bit different. I already have 3 vlans on the dhcp Server, and if I configure only those for dhcp then everything works as expected. The Problem occurs when I want to add the physical device (eth0, untagged) to dhcp, because then, as KEA dhcp Server binds in „raw“ mode, untagged and tagged traffic is delivered via this interface. Because the implementation in KEA dhcp Server does not correctly handle this „mixed“ (untagged/tagged) traffic, it is assigning incorrect ips. I am not sure if using openvswitch can solve that for me.

My hope is that the KEA Team will take care of that and fix it, because in my eyes this is a bug and big Limitation.


Gesendet von Mail für Windows 10
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/kea-users/attachments/20200202/cfb21efe/attachment.htm>

More information about the Kea-users mailing list