[BUG]DHCPClient fails to get DNS address

[mengwei84]

Describe the bug
I use DHCP service to assign IP and DNS addresses, and I operate as a client with DHCPClient. Although I can obtain the IP address, I am unable to retrieve the DNS server address when using the 'nslookup' command.

Here is DHCP service config:
auto-generated by DHCP service (utility.py)
NOTE: move these option lines into the desired pool { } block(s) below
#option domain-name "test.com";
option domain-name-servers 172.31.60.240;
#option routers 10.0.0.1;
log-facility local6;
default-lease-time 600;
max-lease-time 7200;
ddns-update-style none;
subnet 172.31.60.0 netmask 255.255.255.0 {
pool {
range 172.31.60.127 172.31.60.254;
default-lease-time 600;
option routers 172.31.60.252;
}
host mydevice {
hardware ethernet 00:1A:2B:3C:4D:5E;
fixed-address 172.31.60.128;
}
}

Here is DHCPClient config:
#!/bin/sh
#auto-generated by DHCPClient service (utility.py)
#uncomment this mkdir line and symlink line to enable client-side DNS
#resolution based on the DHCP server response.
#mkdir -p /var/run/resolvconf/interface
#ln -s /var/run/resolvconf/interface/eth0.dhclient /var/run/resolvconf/resolv.conf
/sbin/dhclient -nw -pf /var/run/dhclient-eth0.pid -lf /var/run/dhclient-eth0.lease eth0

Here is the operation in DHCPClient:
root@dhcpclient:/tmp/pycore.33285/dhcpclient.conf# nslookup

server
Default server: ::1
Address: ::1#53
Default server: 127.0.0.1
Address: 127.0.0.1#53

Desktop (please complete the following information):

• OS: [Ubuntu 20.04]
• CORE Version [8.2.0]