How do I see what’s changing in my Linux network configuration?

I was trying to find out what changes were being made to my IP V6 network.

The short answer is the command

sudo nmcli general logging level DEBUG domains ALL

and reset it to the default with

sudo nmcli general logging level INFO domains ALL

You see the last 5 minutes worth of trace using

journalctl -u NetworkManager -S -5m >nw.txt

See man NetworkManager.conf.

Debian Man gives slightly different information including

ALL : all log domains
DEFAULT : default log domains
DHCP : shortcut for “DHCP4,DHCP6”
IP : shortcut for “IP4,IP6”

ADSL : ADSL device operations
AGENTS : Secret agents operations and communication
AUDIT : Audit records
AUTOIP4 : AutoIP operations
BOND : Bonding operations
BRIDGE : Bridging operations
BT : Bluetooth operations
CONCHECK : Connectivity check
CORE : Core daemon and policy operations
DBUS_PROPS : D-Bus property changes
DCB : Data Center Bridging (DCB) operations
DEVICE : Activation and general interface operations
DHCP4 : DHCP for IPv4
DHCP6 : DHCP for IPv6
DISPATCH : Dispatcher scripts
DNS : Domain Name System related operations
ETHER : Ethernet device operations
FIREWALL : FirewallD related operations
INFINIBAND : InfiniBand device operations
IP4 : IPv4-related operations
IP6 : IPv6-related operations
MB : Mobile broadband operations
NONE : when given by itself logging is disabled
OLPC : OLPC Mesh device operations
PLATFORM : OS (platform) operations
PPP : Point-to-point protocol operations
PROXY : logging messages for proxy handling
RFKILL : RFKill subsystem operations
SETTINGS : Settings/config service operations
SHARING : Connection sharing. With TRACE level log queries for dnsmasq instance
SUPPLICANT : WPA supplicant related operations
SUSPEND : Suspend/resume
SYSTEMD : Messages from internal libsystemd
TEAM : Teaming operations
VLAN : VLAN operations
VPN : Virtual Private Network connections and operations
VPN_PLUGIN : logging messages from VPN plugins
WIFI : Wi-Fi device operations
WIFI_SCAN : Wi-Fi scanning operations
WIMAX : WiMAX device operations

it produces data like

<debug> [747.1872] ndisc-lndp[...,"eno1"]: received router advertisement at 17121
<debug> ndisc[...,"eno1"]: scheduling next now/lifetime check: 163 seconds
<debug> ndisc[...,"eno1"]: neighbor discovery configuration changed [GAR]:
<debug> ndisc[...,"eno1"]:   dhcp-level none
<debug> ndisc[...,"eno1"]:   hop limit      : 64
<debug> ndisc[...,"eno1"]:   gateway fe80::a2f0:9936:ddfd:95fa pref medium exp 179.8153
<debug> ndisc[...,"eno1"]:   gateway fe80::9b07:33a1:aa30:e272 pref medium exp 162.8153
<debug> ndisc[...,"eno1"]:   address 2001:bbb::573e:5c69:2ab3:4ae6 exp 81751.8153
<debug> ndisc[...,"eno1"]:   address 2001:ccc::dbf:5c90:61a6:20ae exp 86399.8153
<debug> ndisc[...,"eno1"]:   route 2001:db8::99/128 via :: pref medium exp 86399.8153
<debug> ndisc[...,"eno1"]:   route 2001:ff99::/64 via fe80::a2f0:9936:ddfd:95fa pref medium exp 3099.8153
<debug> ndisc[...,"eno1"]:   route 2001:ccc::/64 via :: pref medium exp 86399.8153
<debug> ndisc[...,"eno1"]:   route 2001:bbb::/64 via :: pref medium exp 81751.8153
<debug>  platform: (eno1) route: append     IPv6 route: 2001:db8::/80 via :: dev 2 metric 100 mss 0 rt-src ndisc
<debug>  platform: (eno1) signal: route   6   added: 2001:db8::/80 via :: dev 2 metric 100 mss 0 rt-src rt-ra