networkmanager and dhcl_lease_time

[Andrei Borzenkov]

On 21.06.2024 13:19, Michael Traxler wrote:
> Hello,
> 
> I have the following problem:
> My DHCP-server gives all clients a lease time of
> 86400 seconds.
> 
> I can also see on the clients that this was recognized:
> 
> ufsd3:~ # nmcli connection show main | ag dhcp_lease
> DHCP4.OPTION[3]:                        dhcp_lease_time = 86400
> 
> Now my problem is, that I expect after half a day, a new DHCP request to renew
> the DHCP lease.
> 
> But what I get is, that the clients (many of them) send every 60 seconds a new
> DHCP request:
> 
> # tshark  -i eno2 -f "port 67 or port 68"
>       6 60.354801706 192.168.103.123 → 192.168.100.50 DHCP 325 DHCP Request  - Transaction ID 0x4b7f2ef1
>       7 60.355285370 192.168.105.51 → 192.168.103.123 DHCP 342 DHCP ACK      - Transaction ID 0x4b7f2ef1
>       9 120.697304414 192.168.103.123 → 192.168.100.50 DHCP 325 DHCP Request  - Transaction ID 0xd90c71b5
>      10 120.698068892 192.168.105.51 → 192.168.103.123 DHCP 342 DHCP ACK      - Transaction ID 0xd90c71b5
>      12 181.602768470 192.168.103.123 → 192.168.100.50 DHCP 325 DHCP Request  - Transaction ID 0x97391f7f
>      13 181.603247659 192.168.105.51 → 192.168.103.123 DHCP 342 DHCP ACK      - Transaction ID 0x97391f7f
> 
> Why is that so? Is this a networkmanager issue? Or something else?
> Is it a bug in the distrbution (mainly OpenSuSE Tumbleweed what I use)?
> 
> Any help is appreciated.
> 


DHCP T1 (renewal) timeout can be overridden by server. NetworkManager 
can use external DHCP client so this behavior is beyond NetworkManager 
control and scope. What client is used? Show full DHCP server reply for 
the initial transaction.

I do not observe this behavior on NetworkManager 1.36.6 (Ubuntu 22.04) 
using internal DHCP client.