Public bug reported:

When launching a Focal instance on an single-NIC IPv6 EC2 instance and a
subnet that only allows IPv6, the instance does not bring up networking.
When connecting via the serial console, I find that the interface has no
IP address.

I checked back to 23.4 and this problem is still present there, so this
isn't a recent regression.

Launched with:
aws ec2 run-instances --image-id ami-0e99f6d19f9c4276c --count 1 
--instance-type t3.small --subnet-id <v6-only-subnet> --key-name <my-key> 
--ipv6-address-count 1 --security-group-ids <open-permissions-sg> 
--metadata-options "HttpEndpoint=enabled,HttpProtocolIpv6=enabled"

The rendered netplan config looks like this:
network:
    ethernets:
        ens5:
            dhcp4: true
            dhcp6: true
            match:
                macaddress: 0a:36:7f:80:92:57
            set-name: ens5
    version: 2

I remove the "dhcp4: true" line, network is then able to come up
successfully.

Note that this only happens on Jammy. Comparing Focal and Jammy, the
rendered netplan configurations look exactly the same as well as the
rendered networkd configurations.

I turned on debug logging for networkd, and see different logs in the
journal.

Focal journal logs:
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Acquiring 
DHCPv4 lease
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STARTED on ifindex 2
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Discovering 
IPv6 routers
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: NDISC: Started IPv6 
Router Solicitation client
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State changed: 
pending -> configuring
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): DISCOVER
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: ma
in, proto: ra, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): OFFER
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): REQUEST (requesting)
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): ACK
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): lease expires in 59min 59s
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T2 expires in 52min 29s
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T1 expires in 29min 59s
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCPv4 address 
169.254.100.42/32
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU: 
9001
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Setting transient 
hostname: 'i-0f33f70c994b93ce6'
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Not connected to 
system bus, setting hostname later.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU 
done.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
address 169.254.100.42
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
address: 169.254.100.42/32 (valid for 1h)
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not set 
DHCPv4 route: Nexthop has invalid gateway. Network is unreachable
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Failed
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State changed: 
configuring -> failed
Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STOPPED

Jammy journal logs:
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCPv4 
address 169.254.248.181/32
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
address: 169.254.248.181/32 (valid for 1h, preferred for 1h), flags: n/a
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCP: 
requested route destination 169.254.169.253/32 is not in the assigned network 
169.254.248.181/32, but no gateway is spe>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link layer is configuring.
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: Link state is 
up-to-date
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: State changed: 
initialized -> unmanaged
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_31 
interface=org.freedesktop.DBus.Properti>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: main(254), proto: ra,>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 2600:1f16:fe:9301::/64, src: n/a, gw: n/a, prefsrc: n/a, scope: 
global, table: main(254), proto: ra, t>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
address: 169.254.248.181/32 (valid for 55min 7s, preferred for 55min 7s), 
flags: n/a
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_32 
interface=org.freedesktop.DBus.Properti>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1 
interface=org.freedesktop.DBus.Properties member>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.248.181/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: host, table: local(255), proto>
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: rtnl: received 
non-static neighbor, ignoring.
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: IPv6LL 
address generation mode set.
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: master 
interface set.
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link is not activated.
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Bringing link 
up
Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): DHCP4, DHCP6 or IPv4LL is enabled but no dynamic address is 
assigned yet.

** Affects: cloud-init (Ubuntu)
     Importance: Undecided
         Status: Invalid

** Affects: cloud-init (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Also affects: cloud-init (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Changed in: cloud-init (Ubuntu)
       Status: New => Invalid

** Description changed:

  When launching a Focal instance on an single-NIC IPv6 EC2 instance and a
  subnet that only allows IPv6, the instance does not bring up networking.
  When connecting via the serial console, I find that the interface has no
  IP address.
  
  The rendered netplan config looks like this:
  network:
-     ethernets:
-         ens5:
-             dhcp4: true
-             dhcp6: true
-             match:
-                 macaddress: 0a:36:7f:80:92:57
-             set-name: ens5
-     version: 2
+     ethernets:
+         ens5:
+             dhcp4: true
+             dhcp6: true
+             match:
+                 macaddress: 0a:36:7f:80:92:57
+             set-name: ens5
+     version: 2
  
  I remove the "dhcp4: true" line, network is then able to come up
  successfully.
  
  Note that this only happens on Jammy. Comparing Focal and Jammy, the
  rendered netplan configurations look exactly the same as well as the
  rendered networkd configurations.
  
  I turned on debug logging for networkd, and see different logs in the
  journal.
  
- Focal:
+ Launched with:
+ aws ec2 run-instances --image-id ami-0e99f6d19f9c4276c --count 1 
--instance-type t3.small --subnet-id <v6-only-subnet> --key-name <my-key> 
--ipv6-address-count 1 --security-group-ids <open-permissions-sg> 
--metadata-options "HttpEndpoint=enabled,HttpProtocolIpv6=enabled"
+ 
+ Focal journal logs:
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Acquiring 
DHCPv4 lease
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STARTED on ifindex 2
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Discovering 
IPv6 routers
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: NDISC: Started 
IPv6 Router Solicitation client
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State 
changed: pending -> configuring
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): DISCOVER
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: ma
  in, proto: ra, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): OFFER
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): REQUEST (requesting)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): ACK
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): lease expires in 59min 59s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T2 expires in 52min 29s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T1 expires in 29min 59s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCPv4 
address 169.254.100.42/32
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU: 
9001
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Setting transient 
hostname: 'i-0f33f70c994b93ce6'
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Not connected to 
system bus, setting hostname later.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU 
done.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
address 169.254.100.42
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route: Nexthop has invalid gateway. Network is unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Failed
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State 
changed: configuring -> failed
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STOPPED
  
- 
- Jammy:
+ Jammy journal logs:
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCPv4 
address 169.254.248.181/32
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
address: 169.254.248.181/32 (valid for 1h, preferred for 1h), flags: n/a
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCP: 
requested route destination 169.254.169.253/32 is not in the assigned network 
169.254.248.181/32, but no gateway is spe>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link layer is configuring.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: Link state is 
up-to-date
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: State 
changed: initialized -> unmanaged
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_31 
interface=org.freedesktop.DBus.Properti>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: main(254), proto: ra,>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 2600:1f16:fe:9301::/64, src: n/a, gw: n/a, prefsrc: n/a, scope: 
global, table: main(254), proto: ra, t>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
address: 169.254.248.181/32 (valid for 55min 7s, preferred for 55min 7s), 
flags: n/a
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_32 
interface=org.freedesktop.DBus.Properti>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1 
interface=org.freedesktop.DBus.Properties member>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.248.181/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: host, table: local(255), proto>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: rtnl: received 
non-static neighbor, ignoring.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: IPv6LL 
address generation mode set.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: master 
interface set.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link is not activated.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Bringing 
link up
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): DHCP4, DHCP6 or IPv4LL is enabled but no dynamic address is 
assigned yet.

** Description changed:

  When launching a Focal instance on an single-NIC IPv6 EC2 instance and a
  subnet that only allows IPv6, the instance does not bring up networking.
  When connecting via the serial console, I find that the interface has no
  IP address.
+ 
+ I checked back to 23.4 and this problem is still present there, so this
+ isn't a recent regression.
+ 
+ Launched with:
+ aws ec2 run-instances --image-id ami-0e99f6d19f9c4276c --count 1 
--instance-type t3.small --subnet-id <v6-only-subnet> --key-name <my-key> 
--ipv6-address-count 1 --security-group-ids <open-permissions-sg> 
--metadata-options "HttpEndpoint=enabled,HttpProtocolIpv6=enabled"
  
  The rendered netplan config looks like this:
  network:
      ethernets:
          ens5:
              dhcp4: true
              dhcp6: true
              match:
                  macaddress: 0a:36:7f:80:92:57
              set-name: ens5
      version: 2
  
  I remove the "dhcp4: true" line, network is then able to come up
  successfully.
  
  Note that this only happens on Jammy. Comparing Focal and Jammy, the
  rendered netplan configurations look exactly the same as well as the
  rendered networkd configurations.
  
  I turned on debug logging for networkd, and see different logs in the
  journal.
- 
- Launched with:
- aws ec2 run-instances --image-id ami-0e99f6d19f9c4276c --count 1 
--instance-type t3.small --subnet-id <v6-only-subnet> --key-name <my-key> 
--ipv6-address-count 1 --security-group-ids <open-permissions-sg> 
--metadata-options "HttpEndpoint=enabled,HttpProtocolIpv6=enabled"
  
  Focal journal logs:
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Acquiring 
DHCPv4 lease
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STARTED on ifindex 2
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Discovering 
IPv6 routers
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: NDISC: Started 
IPv6 Router Solicitation client
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State 
changed: pending -> configuring
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): DISCOVER
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: ma
  in, proto: ra, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): OFFER
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): REQUEST (requesting)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): ACK
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): lease expires in 59min 59s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T2 expires in 52min 29s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): T1 expires in 29min 59s
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCPv4 
address 169.254.100.42/32
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU: 
9001
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Setting transient 
hostname: 'i-0f33f70c994b93ce6'
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: Not connected to 
system bus, setting hostname later.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Setting MTU 
done.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route, retrying later: Nexthop has invalid gateway. Network is 
unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: 0, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Removing 
address 169.254.100.42
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Forgetting 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
updated address: 169.254.100.42/32 (valid for 1h)
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Remembering 
route: dst: 169.254.100.42/32, src: n/a, gw: n/a, prefsrc: 169.254.100.42, 
scope: host, table: local, proto: kernel, type: local
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-timesyncd[345]: Network 
configuration changed, trying to establish connection.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Configuring 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.100.42, scope: global, table: main, proto: dhcp, type: unicast
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: DHCP: No 
gateway received from DHCP server.
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Could not 
set DHCPv4 route: Nexthop has invalid gateway. Network is unreachable
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: Failed
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: ens5: State 
changed: configuring -> failed
  Jun 11 15:37:58 i-0f33f70c994b93ce6 systemd-networkd[423]: DHCP CLIENT 
(0xaf38d5c6): STOPPED
  
  Jammy journal logs:
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCPv4 
address 169.254.248.181/32
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
address: 169.254.248.181/32 (valid for 1h, preferred for 1h), flags: n/a
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: DHCP: 
requested route destination 169.254.169.253/32 is not in the assigned network 
169.254.248.181/32, but no gateway is spe>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Requesting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link layer is configuring.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: Link state is 
up-to-date
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: lo: State 
changed: initialized -> unmanaged
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_31 
interface=org.freedesktop.DBus.Properti>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.0.1/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, scope: 
link, table: main(254), proto: dhc>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: n/a, src: n/a, gw: fe80::800:b7ff:fecb:6a7b, prefsrc: n/a, scope: 
global, table: main(254), proto: ra,>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: link, table: main(254), proto:>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.123/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.254/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.253/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 2600:1f16:fe:9301::/64, src: n/a, gw: n/a, prefsrc: n/a, scope: 
global, table: main(254), proto: ra, t>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.250/31, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.169.249/32, src: n/a, gw: 169.254.0.1, prefsrc: 
169.254.248.181, scope: global, table: main(25>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
address: 169.254.248.181/32 (valid for 55min 7s, preferred for 55min 7s), 
flags: n/a
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_32 
interface=org.freedesktop.DBus.Properti>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: Sent message 
type=signal sender=n/a destination=n/a path=/org/freedesktop/network1 
interface=org.freedesktop.DBus.Properties member>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Forgetting 
route: dst: 169.254.248.181/32, src: n/a, gw: n/a, prefsrc: 169.254.248.181, 
scope: host, table: local(255), proto>
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: rtnl: received 
non-static neighbor, ignoring.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: IPv6LL 
address generation mode set.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: master 
interface set.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): link is not activated.
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: Bringing 
link up
  Jun 11 14:57:43 i-0b74a29276ca3fc37 systemd-networkd[1541]: ens5: 
link_check_ready(): DHCP4, DHCP6 or IPv4LL is enabled but no dynamic address is 
assigned yet.

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https://bugs.launchpad.net/bugs/2069066

Title:
  No network access on single-NIC IPv6-only EC2 instance

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