Salut Cyayon,

J'ai testé après plusieurs reboot, le service s'exécute à priori au bon moment :

Sep 11 11:41:40   systemd-networkd[1228]: vlan832: Link UP
Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
[...]
Sep 11 11:41:40   systemd[1]: Starting netdev-egress@vlan832.service - netdev-egress pre-requisite for vlan832...
Sep 11 11:41:40   netdev-egress[1245]: executing nft chain netdev filter egress device vlan832
Sep 11 11:41:40   netdev-egress[1246]: 10: vlan832@ont: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state LOWERLAYERDOWN mode DEFAULT group default qle>
Sep 11 11:41:40   netdev-egress[1246]:     link/ether xxxxxxxxxxxxxx brd ff:ff:ff:ff:ff:ff
[...]
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=signal sender=org.freedesktop.DBus.Local destination=n/a path=/org/freedesktop/DBus/Local interface=org.fre>
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=signal sender=org.freedesktop.DBus destination=:1.7 path=/org/freedesktop/DBus interface=org.freedesktop.DB>
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=signal sender=org.freedesktop.DBus destination=:1.7 path=/org/freedesktop/DBus interface=org.freedesktop.DB>
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.7 path=n/a interface=n/a member=n/a  cookie=429496>
Sep 11 11:41:40   systemd-networkd[1228]: Successfully acquired requested service name.
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.7 path=n/a interface=n/a member=n/a  cookie=429496>
Sep 11 11:41:40   systemd-networkd[1228]: Match type='signal',sender='org.freedesktop.login1',path='/org/freedesktop/login1',interface='org.freedesktop.login1.Manager>
Sep 11 11:41:40   netdev-egress[1247]: Error: No such file or directory
Sep 11 11:41:40   netdev-egress[1247]: list table netdev filter
Sep 11 11:41:40   netdev-egress[1247]:                   ^^^^^^
Sep 11 11:41:40   netdev-egress[1245]: applying netdev filter
Sep 11 11:41:40   audit[1248]: NETFILTER_CFG table=filter:2 family=5 entries=8 op=nft_register_chain pid=1248 subj=system_u:system_r:unconfined_service_t:s0 comm="nft"
Sep 11 11:41:40   netdev-egress[1245]: final nft table netdev filter
Sep 11 11:41:40   netdev-egress[1249]: table netdev filter {
Sep 11 11:41:40   netdev-egress[1249]:         chain egress {
Sep 11 11:41:40   netdev-egress[1249]:                 type filter hook egress device "vlan832" priority filter; policy accept;
Sep 11 11:41:40   netdev-egress[1249]:                 udp dport 547 meta priority set 0:6 ip6 dscp set cs6 comment "Set CoS value to 6 for DHCPv6 packets"
Sep 11 11:41:40   netdev-egress[1249]:                 icmpv6 type { nd-router-solicit, nd-neighbor-solicit, nd-neighbor-advert } meta priority set 0:6 ip6 dscp set c>
Sep 11 11:41:40   netdev-egress[1249]:         }
Sep 11 11:41:40   netdev-egress[1249]: }
Sep 11 11:41:40   netdev-egress[1245]: networkctl status vlan832
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=method_call sender=:1.8 destination=org.freedesktop.network1 path=/org/freedesktop/network1 interface=org.f>
Sep 11 11:41:40   systemd-networkd[1228]: Sent message type=method_return sender=n/a destination=:1.8 path=n/a interface=n/a member=n/a cookie=58 reply_cookie=2 signa>
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=method_call sender=:1.8 destination=org.freedesktop.network1 path=/org/freedesktop/network1/link/_310 inter>
Sep 11 11:41:40   systemd-networkd[1228]: Sent message type=method_return sender=n/a destination=:1.8 path=n/a interface=n/a member=n/a cookie=59 reply_cookie=3 signa>
Sep 11 11:41:40   systemd-networkd[1228]: Got message type=method_call sender=:1.8 destination=org.freedesktop.network1 path=/org/freedesktop/network1/link/_310 inter>
Sep 11 11:41:40   systemd-networkd[1228]: Sent message type=error sender=n/a destination=:1.8 path=n/a interface=n/a member=n/a cookie=60 reply_cookie=4 signature=s e>
Sep 11 11:41:40   netdev-egress[1250]: ● 10: vlan832
Sep 11 11:41:40   netdev-egress[1250]:                    Link File: /usr/lib/systemd/network/99-default.link
Sep 11 11:41:40   netdev-egress[1250]:                 Network File: /etc/systemd/network/30-vlan832.network
Sep 11 11:41:40   netdev-egress[1250]:                        State: no-carrier (configuring)
Sep 11 11:41:40   netdev-egress[1250]:                 Online state: offline
Sep 11 11:41:40   netdev-egress[1250]:                         Type: vlan
Sep 11 11:41:40   netdev-egress[1250]:                         Kind: vlan
Sep 11 11:41:40   netdev-egress[1250]:                       Driver: 802.1Q VLAN Support
Sep 11 11:41:40   netdev-egress[1250]:             Hardware Address: xxxxxxxxxxxxxxxxx (Sagemcom Broadband SAS)
Sep 11 11:41:40   netdev-egress[1250]:                          MTU: 1500 (max: 65535)
Sep 11 11:41:40   netdev-egress[1250]:                        QDisc: noqueue
Sep 11 11:41:40   netdev-egress[1250]: IPv6 Address Generation Mode: eui64
Sep 11 11:41:40   netdev-egress[1250]:                      VLan Id: 832
Sep 11 11:41:40   netdev-egress[1250]:     Number of Queues (Tx/Rx): 1/1
Sep 11 11:41:40   netdev-egress[1250]:             Auto negotiation: no
Sep 11 11:41:40   netdev-egress[1250]:                         Port: fibre
Sep 11 11:41:40   netdev-egress[1250]:            Activation Policy: up
Sep 11 11:41:40   netdev-egress[1250]:          Required For Online: yes
Sep 11 11:41:41   avahi-daemon[884]: Joining mDNS multicast group on interface lan.IPv6 with address  fe80::yyyyyyyyyy.
Sep 11 11:41:41   avahi-daemon[884]: New relevant interface lan.IPv6 for mDNS.
Sep 11 11:41:41   systemd-networkd[1228]: lan: Received new foreign address (configured):  fe80::yyyyyyyyyy/64 (valid forever, preferred forever), flags: perm>
Sep 11 11:41:41   avahi-daemon[884]: Registering new address record for  fe80::yyyyyyyyyy on lan.*.
Sep 11 11:41:41   systemd-networkd[1228]: lan: Gained IPv6LL
Sep 11 11:41:41   systemd-networkd[1228]: lan: Discovering IPv6 routers
Sep 11 11:41:41   systemd-networkd[1228]: lan: NDISC: Started IPv6 Router Solicitation client
Sep 11 11:41:41   systemd-networkd[1228]: lan: State changed: configuring -> configured
Sep 11 11:41:41   systemd-networkd[1228]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_32 interface=org.freedesktop.DBus.P>
Sep 11 11:41:41   systemd-networkd[1228]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_32 interface=org.freedesktop.DBus.P>
Sep 11 11:41:41   systemd-networkd[1228]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1 interface=org.freedesktop.DBus.Properties>
Sep 11 11:41:41   systemd-networkd[1228]: lan: Starting IPv6 Router Advertisements
Sep 11 11:41:41   systemd-networkd[1228]: lan: RADV: Started IPv6 Router Advertisement daemon
Sep 11 11:41:41   systemd-networkd[1228]: lan: IPv6 Router Advertisement engine is configured and started.
Sep 11 11:41:41   systemd-networkd[1228]: lan: Received new foreign route (configured): dst:  fe80::yyyyyyyyyy/128, src: n/a, gw: n/a, prefsrc: n/a, scope: gl>
Sep 11 11:41:41   systemd-networkd[1228]: lan: RADV: Next Router Advertisement in 6s
Sep 11 11:41:41   systemd-networkd[1228]: lan: Received new foreign route (configured): dst: fe80::/128, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: local(>
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): link is not activated.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): link is not activated.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): link is not activated.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): link is not activated.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): link is not activated.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: Bringing link up
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: found matching network '/etc/systemd/network/30-vlan832.network'.
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: Flags change: +UP
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: Link UP
Sep 11 11:41:41   netdev-egress[1250]: Sep 11 11:41:40   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:41   systemd[1]: Finished netdev-egress@vlan832.service - netdev-egress pre-requisite for vlan832.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: Received new foreign route (configured): dst: ff00::/8, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: loca>
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: Received new foreign route (configured): dst: fe80::/64, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: mai>
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: Flags change: +LOWER_UP +RUNNING
Sep 11 11:41:44   systemd-networkd[1228]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_310 interface=org.freedesktop.DBus.>
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: Gained carrier
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: found matching network '/etc/systemd/network/30-vlan832.network'.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: LLDP Rx: Started LLDP client
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: link_check_ready(): IPv6LL is not configured yet.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: DHCPv4 client: STARTED on ifindex 10
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: DHCPv4 client is configured, acquiring DHCPv4 lease.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: IPv6 link-local address is not set, delaying to start DHCPv6 client.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: DHCPv6 client is configured.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: IPv6 Router Discovery is configured.
Sep 11 11:41:44   systemd-networkd[1228]: ont: Received updated static address (configured): 192.168.1.254/24 broadcast 192.168.1.255 (valid forever, preferred foreve>
Sep 11 11:41:44   systemd-networkd[1228]: ont: link_check_ready(): static addresses are not configured.
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: DHCPv4 client: DISCOVER
Sep 11 11:41:44   systemd-networkd[1228]: vlan832: DHCPv4 client: State changed: initialization -> selecting
Sep 11 11:41:44   systemd-networkd[1228]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_310 interface=org.freedesktop.DBus.>
Sep 11 11:41:44   systemd-networkd[1228]: ont: Addresses set
Sep 11 11:41:44   systemd-networkd[1228]: ont: State changed: configuring -> configured

L'interface vlan832 est créée et c'est appliqué avant le "Link UP" et les client DHCP sont lancé par la suite.

Est-ce que tu pensais à une autre configuration ?