[Bug]: DHCP adds invalid DNS server entries to guest with an IPv6 NS on host

[sebix]

Version

7.2.8

Host OS Type

Linux

Host OS name + version

Debian 12 bookworm

Host Architecture

x86

Guest OS Type

Linux

Guest Architecture

x86

Guest OS name + version

Debian 13 trixie

Component

Network

What happened?

The Virtual Box's DHCP distributes the invalid DNS server addresses 2.127.0.0 and fd17:625c:f037:2::3 when the file /etc/resolv.conf on the host contains the IPv6 address of the nameserver. That results in delays in the name resolution.

We don't know what causes VBox to add these addresses.

Before the host virtualbox upgrade from 7.2.4 to 7.2.8, the same problem appeared too.

The complete /etc/resolv.conf in the guest, containing the bogus addresses:

# cat /etc/resolv.conf 
# Generated by dhcpcd from enp0s3.dhcp, enp0s3.ra
# /etc/resolv.conf.head can replace this line
domain hq.intevation.de
search hq.intevation.de ipv6.intevation.de intevation.de
nameserver 2.127.0.0
nameserver 192.168.11.254
nameserver 192.168.11.11
nameserver fd17:625c:f037:2::3
# /etc/resolv.conf.tail can replace this line

The content comes clearly from DHCP:

# dhcpcd --dumplease enp0s3
[...]
reason=BOUND
interface=enp0s3
protocol=dhcp
ip_address=10.0.2.15
subnet_cidr=24
broadcast_address=10.0.2.255
network_number=10.0.2.0
subnet_mask=255.255.255.0
routers=10.0.2.2
domain_name_servers=2.127.0.0 192.168.11.254 192.168.11.11
domain_name=int.example.com
dhcp_lease_time=86400
dhcp_message_type=5
dhcp_server_identifier=10.0.2.2
domain_search=int.example.com ipv6.example.com example.com
[...]

On the host:

$ VBoxManage list dhcpservers
NetworkName:    HostInterfaceNetworking-vboxnet0
Dhcpd IP:       192.168.56.100
LowerIPAddress: 192.168.56.101
UpperIPAddress: 192.168.56.254
NetworkMask:    255.255.255.0
Enabled:        Yes
Global Configuration:
    minLeaseTime:     default
    defaultLeaseTime: default
    maxLeaseTime:     default
    Forced options:   None
    Suppressed opts.: None
        1/legacy: 255.255.255.0
Groups:               None
Individual Configs:   None

NetworkName:    NatNetwork
Dhcpd IP:       10.0.2.3
LowerIPAddress: 10.0.2.4
UpperIPAddress: 10.0.2.254
NetworkMask:    255.255.255.0
Enabled:        Yes
Global Configuration:
    minLeaseTime:     default
    defaultLeaseTime: default
    maxLeaseTime:     default
    Forced options:   None
    Suppressed opts.: None
        1/legacy: 255.255.255.0
        3/legacy: 10.0.2.1
        6/legacy: 192.168.11.254 192.168.11.11
       15/legacy: int.example.com
Groups:               None
Individual Configs:   None

How can we reproduce this?

Adding a IPv6 nameserver on the VBox host's /etc/resolv.conf?

Not entirely clear if that's the direct cause or some special behavior related to this is the actual cause.

Did you upload all of your necessary log files, screenshots, etc.?

• Yes, I've uploaded all pertinent files to this issue.