Wrong DHCP-Adress when switching VLANs

paddex

8/27/24, 12:43 PM

I have a problem with our fairly new kea-dhcp setup. We have a bunch of different VLANs in use for which we want to give out DHCP-Adresses. For this purpose we use a little APU-box which serves our kea-dhcp4. This APU-box has on port on which all the different VLANs are tagged. I then setup the config, so I give out different IP-Adress-Pools for each VLAN. This is how I configured the different subnets:

{
    "subnet": "10.14.70.0/24",

    "interface": "enp3s0.70",

    "pools": [
            {
                     "pool": "10.14.70.100-10.14.70.199"
            }
    ],

    "option-data": [
            {
                    "name": "routers",
                    "data": "10.14.70.254"
            }
    ],

    "reservations": [
            {
                    "hw-address": "xx:xx:xx:xx:xx:xx",
                    "ip-address": "10.14.70.200"
            },
            {
                    "hw-address": "yy:yy:yy:yy:yy:yy",
                    "ip-address": "10.14.70.11"
            }
    ]


}

This works and I am happy with the results.
The problem happens when I put my Laptop from one VLAN into another. KEA does not seem to check which VLAN I am connected to when it already knows my MAC-Adress. If I switch from VLAN 70 to 71, instead of getting a fresh IP form the VLAN-71 subnet, I still get my old IP from the 70 subnet. This leads to me not being able to connect to the network unless I manually release my IP and request a new one.

Is there some configuration-option I can enable, so KEA always checks the interface from which the request originates? Or is there some other way around this issue?

Thank you

0 + 3

dhcp

dhcp-server

Jaromanda X

8/27/24, 11:27 PM

If manually renewing the DHCP lease works, then the DHCP server is functioning as it should. You need to manually renew the DHCP lease, because DHCP leases last for a certain amount of time, the client won't renew the lease (i.e. contact the DHCP server) until it needs to based on the time. Your assumption that *KEA does not seem to check which VLAN I am connected to* is therefore incorrect, since the client isn't actually contacting the DHCP server until it needs to renew the IP address

Mucker

8/28/24, 10:17 AM

To add to @JaromandaX comments, you are probably switching vlans digitally (or some other method I am not aware of). If you were to switch vlans in the traditional sense (unlug the cable/disconnet WIFI), the network card on your device would automatically release the IP address and get a new one when you "plug it back" to the other vlan. I can only guess that you are not doing this (or the digital equivelent of this assuming it is a vNIC)

paddex

8/28/24, 7:21 PM

That's literally what I am doing though...to switch the VLAN I have to physically put the ethernet cable into another outlet.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Wrong DHCP-Adress when switching VLANs

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.