Reproducer with DHCP server/client on LXD. [Jammy]

Bridge
---

	sudo ip link add jammybr type bridge
	sudo ip link set jammybr up



LXD container for DHCP server with classless static routes option
---

	lxc init ubuntu:jammy jammy-dhcpd
	lxc config device add jammy-dhcpd eth0 nic nictype=bridged parent=jammybr
	lxc config device add jammy-dhcpd eth1 nic nictype=bridged parent=lxdbr0

	lxc start jammy-dhcpd
	lxc shell jammy-dhcpd

	dhclient eth1

...

	ip addr add 10.11.12.13/24 dev eth0

	apt install -y isc-dhcp-server

	echo 'INTERFACESv4="eth0"' >>/etc/default/isc-dhcp-server

	cat <<EOF >>/etc/dhcp/dhcpd.conf
	option rfc3442-classless-static-routes code 121 = array of integer 8;

	subnet 10.11.12.0 netmask 255.255.255.0 {

	  range 10.11.12.100 10.11.12.110;

	  option routers 10.11.12.13;

	  option rfc3442-classless-static-routes
	    0,              10, 11, 12, 200,
	    8,  1,          10, 11, 12, 208,
	    16, 2, 1,       10, 11, 12, 216,
	    24, 3, 2, 1,    10, 11, 12, 224,
	    32, 4, 3, 2, 1, 10, 11, 12, 232;
	}
	EOF

	systemctl restart isc-dhcp-server.service



LXD VM for DHCP client
---

	lxc init ubuntu:jammy jammy-dhclient --vm
	lxc config device add jammy-dhclient eth0 nic nictype=bridged parent=jammybr
	# no regular lxdbr0 bridge / internet access.

	lxc start jammy-dhclient
	lxc shell jammy-dhclient

	# ip link
	...
	2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff

	# ip addr
	...
	2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff
	    inet 10.11.12.102/24 metric 100 brd 10.11.12.255 scope global dynamic enp5s0
	       valid_lft 551sec preferred_lft 551sec
	    inet6 fe80::216:3eff:fee8:3e4d/64 scope link
	       valid_lft forever preferred_lft forever

	# ip route
	default via 10.11.12.200 dev enp5s0 proto dhcp src 10.11.12.102 metric 100
	1.0.0.0/8 via 10.11.12.208 dev enp5s0 proto dhcp src 10.11.12.102 metric 100
	2.1.0.0/16 via 10.11.12.216 dev enp5s0 proto dhcp src 10.11.12.102 metric 100
	3.2.1.0/24 via 10.11.12.224 dev enp5s0 proto dhcp src 10.11.12.102 metric 100
	4.3.2.1 via 10.11.12.232 dev enp5s0 proto dhcp src 10.11.12.102 metric 100
	10.11.12.0/24 dev enp5s0 proto kernel scope link src 10.11.12.102 metric 100
	10.11.12.200 dev enp5s0 proto dhcp scope link src 10.11.12.102 metric 100
	10.11.12.208 dev enp5s0 proto dhcp scope link src 10.11.12.102 metric 100
	10.11.12.216 dev enp5s0 proto dhcp scope link src 10.11.12.102 metric 100
	10.11.12.224 dev enp5s0 proto dhcp scope link src 10.11.12.102 metric 100
	10.11.12.232 dev enp5s0 proto dhcp scope link src 10.11.12.102 metric 100

Ok, all good from booted system's perspective.

Let's check at initramfs time, manually.

The classless routes aren't added if you run dhclient at the current version.

	cat <<EOF >/etc/default/grub.d/99-grub-initrd.cfg
	GRUB_FORCE_PARTUUID=
	GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT console=ttyS0 break=bottom"
	EOF

	update-grub && poweroff

	lxc start --console jammy-dhclient

	(initramfs) ip addr
	1: lo: <LOOPBACK> mtu 65536 qdisc noop qlen 1000
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	2: enp5s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff

	(initramfs) ip route
	(initramfs) 

	(initramfs) dhclient enp5s0
	sed: /etc/resolv.conf: No such file or directory

	(initramfs) ip addr
	1: lo: <LOOPBACK> mtu 65536 qdisc noop qlen 1000
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff
	    inet 10.11.12.103/24 brd 10.11.12.255 scope global enp5s0
	       valid_lft forever preferred_lft forever
	    inet6 fe80::216:3eff:fee8:3e4d/64 scope link
	       valid_lft forever preferred_lft forever

	(initramfs) ip route
	10.11.12.0/24 dev enp5s0 scope link  src 10.11.12.103

	(initramfs) dhclient -r enp5s0
	(initramfs) exit


Test package (download it from dhcp server container)
---

@ jammy-dhcpd:
	add-apt-repository -y ppa:mfo/lp1926139
	apt download isc-dhcp-client
	python3 -m http.server

@ jammy-dhclient:

	wget 10.11.12.13:8000/isc-dhcp-client_4.4.1-2.3ubuntu2.4_amd64.deb
	dpkg -i isc-dhcp-client_4.4.1-2.3ubuntu2.4_amd64.deb

Update the initramfs:

	# lsinitramfs /boot/initrd.img-$(uname -r) | grep dhclient-exit-hooks.d
	#

	update-initramfs -u

	# lsinitramfs /boot/initrd.img-$(uname -r) | grep dhclient-exit-hooks.d
	etc/dhcp/dhclient-exit-hooks.d
	etc/dhcp/dhclient-exit-hooks.d/rfc3442-classless-routes

	# poweroff

Try again:

	lxc start --console jammy-dhclient

The classless routes ARE added if you run dhclient with the test package.

	(initramfs) ip addr
	1: lo: <LOOPBACK> mtu 65536 qdisc noop qlen 1000
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	2: enp5s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff
	    
	(initramfs) ip route
	(initramfs)

	(initramfs) dhclient enp5s0
	sed: /etc/resolv.conf: No such file or directory

	(initramfs) ip addr
	1: lo: <LOOPBACK> mtu 65536 qdisc noop qlen 1000
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff
	    inet 10.11.12.104/24 brd 10.11.12.255 scope global enp5s0
	       valid_lft forever preferred_lft forever
	    inet6 fe80::216:3eff:fee8:3e4d/64 scope link
	       valid_lft forever preferred_lft forever

	(initramfs) ip route
	default via 10.11.12.200 dev enp5s0
	1.0.0.0/8 via 10.11.12.208 dev enp5s0
	2.1.0.0/16 via 10.11.12.216 dev enp5s0
	3.2.1.0/24 via 10.11.12.224 dev enp5s0
	4.3.2.1 via 10.11.12.232 dev enp5s0
	10.11.12.0/24 dev enp5s0 scope link  src 10.11.12.104

	(initramfs) dhclient -r enp5s0
	(initramfs) exit

Now let's check that `ip=dhcp` is working (break=init stops after it runs):

	cat <<EOF >/etc/default/grub.d/99-grub-initrd.cfg
	GRUB_FORCE_PARTUUID=
	GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT console=ttyS0 ip=dhcp break=init"
	EOF

	update-grub && poweroff

	lxc start --console jammy-dhclient

And yes, it is.

	(initramfs) ip addr
	1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
	    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
	    inet 127.0.0.1/8 scope host lo
	       valid_lft forever preferred_lft forever
	    inet6 ::1/128 scope host
	       valid_lft forever preferred_lft forever
	2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000
	    link/ether 00:16:3e:e8:3e:4d brd ff:ff:ff:ff:ff:ff
	    inet 10.11.12.104/24 brd 10.11.12.255 scope global eth0
	       valid_lft forever preferred_lft forever
	    inet6 fe80::216:3eff:fee8:3e4d/64 scope link
	       valid_lft forever preferred_lft forever

	(initramfs) ip route
	default via 10.11.12.13 dev eth0
	1.0.0.0/8 via 10.11.12.208 dev eth0
	2.1.0.0/16 via 10.11.12.216 dev eth0
	3.2.1.0/24 via 10.11.12.224 dev eth0
	4.3.2.1 via 10.11.12.232 dev eth0
	10.11.12.0/24 dev eth0 scope link  src 10.11.12.104

	(initramfs)


Clean up:

	lxc stop ...
	lxc delete ...
	sudo ip link del jammybr