1

what i want

my setup has a dynamic amount of LXC containers and therefore i need some dynamic ipv6 address allocation. the interface brNC-internet is a simple bridge which is mapped into the LXC based container.

i need a way to assign ipv6 addresses in LXC containers to the internet interface of each. manually doing so works, as shown below but this should be automated using dhcpd6 (or something similar).

i'd love to try:

  • stateful dhcp: where a client is reassigned the same address when rebooted within some time limit (days, weeks)
  • stateless dhcp: a client gets just any address for the time it is up

note: i can't use radvd with SLAAC because my network prefix is /66 and radvd requires at least a /64 for this, see this.

note: i'd like to focus on ipv6 for the moment.

note: i'm using nixos linux and i did probably just configure something wrongly, have a firewall rule which breaks things or a general misunderstanding about ipv6 or even some LXC specific internal. in either case, please point out what i could be trying next.

my problem

i've setup radvd and dhcpd6 on the host (a VM) but while radvd is able to push a ipv6 default gateway and a prefix the client never seems to talk to the dhcpd6 server using dhcpcd from the client.

if i disable the dhcpcd client on the guest LXC instance i can assign a ipv6 address within the prefix and ping6 to google works:

[root@10:/]# ip a replace 2a01:4f8:221:3744:4000::4 dev internet

[root@10:/]# ping -6 -I internet 2a00:1450:4001:80b::2003
PING 2a00:1450:4001:80b::2003(2a00:1450:4001:80b::2003) from fe80::10af:ffff:fef4:318a internet: 56 data bytes
From fe80::2044:c6ff:fef3:cd5d%internet icmp_seq=1 Destination unreachable: Beyond scope of source address
64 bytes from 2a00:1450:4001:80b::2003: icmp_seq=2 ttl=55 time=5.36 ms
64 bytes from 2a00:1450:4001:80b::2003: icmp_seq=3 ttl=55 time=5.26 ms
64 bytes from 2a00:1450:4001:80b::2003: icmp_seq=4 ttl=55 time=5.27 ms

i've also tried to disable the firewalls on both host and LXC client but no change.

dhcpcd from lxc

dhcpcd -6  --config /nix/store/7n7ysqf92rlafihs9dm2gzsbh06cw64z-dhcpcd.conf
DUID 00:01:00:01:22:4f:af:36:ee:ae:40:b5:d7:d3
internet: IAID 98:0e:c7:c8
internet: soliciting an IPv6 router
internet: Router Advertisement from fe80::2044:c6ff:fef3:cd5d
forked to background, child pid 1238

tcpdump on the VM

tcpdump -i brNC-internet ip6



14:36:18.618554 IP6 fe80::dc5d:98ff:fe0e:c7c8 > ff02::2: ICMP6, router solicitation, length 16
14:36:18.618681 IP6 status.nixcloud.io > fe80::dc5d:98ff:fe0e:c7c8: ICMP6, router advertisement, length 112
14:36:20.578582 IP6 status.nixcloud.io > ff02::1: ICMP6, router advertisement, length 112
14:36:24.059514 IP6 status.nixcloud.io > fe80::dc5d:98ff:fe0e:c7c8: ICMP6, neighbor solicitation, who has fe80::dc5d:98ff:fe0e:c7c8, length 32
14:36:24.059598 IP6 fe80::dc5d:98ff:fe0e:c7c8 > status.nixcloud.io: ICMP6, neighbor advertisement, tgt is fe80::dc5d:98ff:fe0e:c7c8, length 24

dhcpd6 log on the vm

journalctl -u dhcpd6 -f
-- Logs begin at Tue 2018-02-13 02:31:51 CET. --
Mar 30 14:00:08 status.nixcloud.io dhcpd[17605]: Wrote 0 NA, 0 TA, 0 PD leases to lease file.
Mar 30 14:00:08 status.nixcloud.io dhcpd6[17605]: Bound to *:547
Mar 30 14:00:08 status.nixcloud.io dhcpd[17605]: Bound to *:547
Mar 30 14:00:08 status.nixcloud.io dhcpd[17605]: Listening on Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Mar 30 14:00:08 status.nixcloud.io dhcpd[17605]: Sending on   Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Mar 30 14:00:08 status.nixcloud.io dhcpd6[17605]: Listening on Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Mar 30 14:00:08 status.nixcloud.io dhcpd6[17605]: Sending on   Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Mar 30 14:00:08 status.nixcloud.io systemd[1]: dhcpd6.service: Can't open PID file /run/dhcpd6/dhcpd.pid (yet?) after start: No such file or directory
Mar 30 14:00:08 status.nixcloud.io dhcpd6[17615]: Server starting service.
Mar 30 14:00:08 status.nixcloud.io systemd[1]: Started DHCPv6 server.

my setup

host vm

ip -6 a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2a01:4f8:221:3744::1:26/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fefb:d8d0/64 scope link
       valid_lft forever preferred_lft forever
3: enp0s2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::5054:ff:fe08:4db9/64 scope link
       valid_lft forever preferred_lft forever
4: brNC-hostonly: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::5880:6aff:fe77:cd16/64 scope link
       valid_lft forever preferred_lft forever
5: brNC-internet: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2a01:4f8:221:3744:4000::2/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fc00::261/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::2044:c6ff:fef3:cd5d/64 scope link
       valid_lft forever preferred_lft forever
121: vethVIEF2K@if120: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::fc55:8fff:fe5d:a50a/64 scope link
       valid_lft forever preferred_lft forever
123: vethPIKVFW@if122: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::fc4f:adff:fe61:180b/64 scope link
       valid_lft forever preferred_lft forever
133: vethC387B7@if132: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::fc5c:16ff:fe64:444b/64 scope link
       valid_lft forever preferred_lft forever
135: vethE0I0FG@if134: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::fcbf:d4ff:fe33:a9d0/64 scope link
       valid_lft forever preferred_lft forever


ip -6 r
2a01:4f8:221:3744::1:26 dev enp0s3 proto kernel metric 256 pref medium
2a01:4f8:221:3744:4000::2 dev brNC-internet proto kernel metric 256 pref medium
2a01:4f8:221:3744:4000::/66 dev brNC-internet proto kernel metric 256 expires 9700sec pref medium
fc00::26 dev enp0s3 metric 1024 pref medium
fc00::261 dev brNC-internet proto kernel metric 256 pref medium
fe80::/64 dev enp0s3 proto kernel metric 256 pref medium
fe80::/64 dev brNC-hostonly proto kernel metric 256 pref medium
fe80::/64 dev brNC-internet proto kernel metric 256 pref medium
fe80::/64 dev enp0s2 proto kernel metric 256 pref medium
fe80::/64 dev vethVIEF2K proto kernel metric 256 pref medium
fe80::/64 dev vethPIKVFW proto kernel metric 256 pref medium
fe80::/64 dev vethE0I0FG proto kernel metric 256 pref medium
fe80::/64 dev vethC387B7 proto kernel metric 256 pref medium
default via fc00::26 dev enp0s3 metric 1024 pref medium

dhcpd configuration

cat /nix/store/5zvcjwvlj9n7cvrppkw1mxsxwhxwx3cm-dhcpd.conf
default-lease-time 600;
max-lease-time 7200;
authoritative;
ddns-update-style interim;
log-facility local1; # see dhcpd.nix

subnet6 2a01:4f8:221:3744:4000::/66 {
  #range6 2a01:4f8:221:3744:4000::/66 temporary;
  option dhcp6.name-servers 2a01:4f8:0:1::add:1010, 2a01:4f8:0:1::add:9999, 2a01:4f8:0:1::add:9898;
}

radvd configuration

cat /nix/store/89j6hg4qhnd9nyijf9p2dcr4f5ygjz6r-radvd.conf
interface brNC-internet {
  AdvSendAdvert on;
  MinRtrAdvInterval 3; 
  MaxRtrAdvInterval 10;
  prefix 2a01:4f8:221:3744:4000::/66 {
    AdvOnLink on; 
    AdvAutonomous off; 
  };
  RDNSS 2a01:4f8:0:1::add:1010 2a01:4f8:0:1::add:9999 2a01:4f8:0:1::add:9898 { };
};

guest LXC

[root@10:/]# ip -6 a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
132: hostonly@if133: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::484f:50ff:fe0c:fa62/64 scope link 
       valid_lft forever preferred_lft forever
134: internet@if135: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2a01:4f8:221:3744:4000::4/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::10af:ffff:fef4:318a/64 scope link 
       valid_lft forever preferred_lft forever

[root@10:/]# ip -6 r
2a01:4f8:221:3744:4000::4 dev internet proto kernel metric 256 pref medium
2a01:4f8:221:3744:4000::/66 dev internet proto kernel metric 256 expires 86395sec pref medium
fe80::/64 dev hostonly proto kernel metric 256 pref medium
fe80::/64 dev internet proto kernel metric 256 pref medium
default via fe80::2044:c6ff:fef3:cd5d dev internet proto ra metric 1024 expires 25sec hoplimit 64 pref medium

lxc config

lxc.uts.name = 10

# Fixme also support other architectures?
lxc.arch = x86_64
# Not needed, just makes spares a few cpu cycles as LXC doesn't have
# to detect the backend.
#lxc.rootfs.backend = dir
lxc.rootfs.path = /var/lib/lxc/10/rootfs
lxc.init.cmd = /init/container/init
#lxc.rootfs = /var/lib/lxc/10/rootfs

# Ensures correct functionality with user namespaces. Since mknod is not possible stuff like
# /dev/console, /dev/tty, /dev/urandom, etc. need to be bind mounted. Note the order
# of the file inclusion here is important.
lxc.include = /nix/store/3hz7xkd86pzrvr4z53fa079q61qar02x-lxc-2.1.1/share/lxc/config/common.conf
lxc.include = /nix/store/3hz7xkd86pzrvr4z53fa079q61qar02x-lxc-2.1.1/share/lxc/config/userns.conf

## Network
# see also https://wiki.archlinux.org/index.php/Linux_Containers
lxc.net.0.type = veth
lxc.net.0.name = hostonly
#lxc.net.0.ipv4.address = 10.101.0.63 (we assign this using nix, not from lxc)
lxc.net.0.flags = up
lxc.net.0.link = brNC-hostonly

lxc.net.1.type = veth
lxc.net.1.name = internet 
lxc.net.1.flags = up
lxc.net.1.link = brNC-internet


# Specifiy {u,g}id mapping.
lxc.idmap = u 0 100000 65536
lxc.idmap = g 0 100000 65536

# FIXME apparmor support
# Nixos does not provide AppArmor support.
#lxc.aa_profile = unconfined
#lxc.aa_allow_incomplete = 1
lxc.apparmor.profile = unconfined
lxc.apparmor.allow_incomplete = 1

# Tweaks for systemd.
lxc.autodev = 1

# Additional mount entries.
lxc.mount.entry = /nix/store nix/store none defaults,bind.ro 0.0
lxc.mount.entry = /nix/var/nix/profiles/nixcloud-container-10 init none defaults,bind.ro 0 0

# Mount entries that lead to a cleaner boot experience.
lxc.mount.entry = /sys/kernel/debug sys/kernel/debug none bind,optional 0 0
lxc.mount.entry = /sys/kernel/security sys/kernel/security none bind,optional 0 0
lxc.mount.entry = /sys/fs/pstore sys/fs/pstore none bind,optional 0 0
lxc.mount.entry = mqueue dev/mqueue mqueue rw,relatime,create=dir,optional 0 0

# LXC autostart
lxc.start.auto = 0


lxc.rootfs.path = dir:/var/lib/lxc/10/rootfs
1

ok, here we go:

after 3 full days of trying different configurations, reading about 40 webpages and a hell of luck, here is how i got it working:

  • needed a special dhcpcd.conf (default won't work)
  • needed a special dhcpd6.conf (default won't work either)
  • needed a special radvd.conf (there was no default)
  • and only with the nixos firewall disabled (will post the rules modification when i found out what needs to be done) -> systemctl stop firewall

the missing firewall rules in the nixos firewall were those:

ip6tables -A INPUT -p tcp -m tcp -m multiport -i brNC-internet -j ACCEPT --dports 546,547
ip6tables -A INPUT -p udp -m udp -m multiport -i brNC-internet -j ACCEPT --dports 546,547

summary: the state of ipv6 documentation, ipv6 default configurations (in ubuntu server) and best practices guides is a shame and shows once more why ipv6 it is not deployed on more sites and with that i mean servers (not even talking about client configurations as laptops or mobile devices here).

my current setup deploys the ipv6 gateway via radvd and assigns ipv6 addresses using dhcpd6 in parallel as SLAAC can't be used in my setup as my prefix is /66 and needs to be (/64, /63, ..., a smaller number than 64). see http://www.teaparty.net/technotes/home-ipv6.html (section radvd) for more details.

note on dhclient: oh, and unlike dhcpcd which requires a very special configuration to work using dhclient on my ubuntu test machines i got a lease without any modification to the dhclient configuration. this is a huge plus compared to the dhcpcd implementation.

documentation

note on documentations and blogs: thanks so much to sixxs.net and the authors of these webpages. without your great work i couldn't have made it!

radvd configuration

  interface brNC-internet {
    AdvSendAdvert on;
    MinRtrAdvInterval 3;
    MaxRtrAdvInterval 10;
    #prefix 2a01:4f8:221:3744:4000::/66 {
    #  AdvOnLink on;
    #  AdvAutonomous off;
    #};
    #RDNSS 2a01:4f8:0:1::add:1010 2a01:4f8:0:1::add:9999 2a01:4f8:0:1::add:9898 { };

dhcpcd output

[root@11:~]# dhcpcd --config /root/dhcpcd6.conf 
DUID 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6
internet: IAID fc:bf:59:37
internet: IAID 00:00:00:01
internet: confirming prior DHCPv6 lease
internet: REPLY6 received from fe80::e4d2:fbff:feab:81dd
internet: adding address 2a01:4f8:221:3744:4000::300/128
internet: renew in 40000, rebind in 64000, expire in 86400 seconds
forked to background, child pid 12363

dhcpcd.conf (client configuration)

# Inform the DHCP server of our hostname for DDNS.
hostname

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# options to request from the DHCP
option domain_name_servers, interface_mtu

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# only configure ipv6
ipv6only

# disable routing solicitation
noipv6rs

# don't touch these interfaces at all
denyinterfaces hostonly

interface internet
 # enable routing solicitation get the default IPv6 route
 #ipv6rs
 # request a normal (IA_NA) IPv6 address with IAID 1
 ia_na 1

dhcpd6 configuration

  services.dhcpd6 = {
    enable = true;
    interfaces = [ "brNC-internet" ];
    extraConfig = ''
      ddns-update-style interim;
      ddns-updates on;
      ddns-domainname "your.domain.com";
      ddns-rev-domainname "ip6.arpa";
      allow client-updates;
      update-conflict-detection false;
      update-optimization false;
      authoritative;
      option domain-name-servers dns.your.domain.com;
      default-lease-time 86400;
      preferred-lifetime 80000;
      allow leasequery;
      option dhcp6.name-servers 2001:0db8:edfa:1234::1;
      option dhcp6.domain-search "your.domain.com","domain.com";
      #include "/etc/rndc.key";
      option dhcp6.preference 255;

      subnet6 2a01:4f8:221:3744:4000::/66 {
        #range6 2a01:4f8:221:3744:4000::/66 temporary;
        range6 2a01:4f8:221:3744:4000::129 2a01:4f8:221:3744:4000::300;
        option dhcp6.name-servers 2a01:4f8:0:1::add:1010, 2a01:4f8:0:1::add:9999, 2a01:4f8:0:1::add:9898;
        # option dhcp6.gateway 2001:db8:2:3::1;
      } 
    ''; 
  };

tcpdump output

tcpdump -i brNC-internet ip6
13:47:01.854794 IP6 fe80::d4e8:fcff:febf:5937 > status.nixcloud.io: ICMP6, neighbor solicitation, who has status.nixcloud.io, length 32
13:47:01.854827 IP6 status.nixcloud.io > fe80::d4e8:fcff:febf:5937: ICMP6, neighbor advertisement, tgt is status.nixcloud.io, length 24
13:47:05.649860 IP6 status.nixcloud.io > ff02::1: ICMP6, router advertisement, length 24
13:47:06.772849 IP6 fe80::d4e8:fcff:febf:5937.dhcpv6-client > ff02::1:2.dhcpv6-server: dhcp6 solicit
13:47:06.773021 IP6 status.nixcloud.io.dhcpv6-server > fe80::d4e8:fcff:febf:5937.dhcpv6-client: dhcp6 advertise
13:47:06.773344 IP6 fe80::d4e8:fcff:febf:5937.dhcpv6-client > ff02::1:2.dhcpv6-server: dhcp6 request
13:47:06.774004 IP6 status.nixcloud.io.dhcpv6-server > fe80::d4e8:fcff:febf:5937.dhcpv6-client: dhcp6 reply
13:47:06.777782 IP6 fe80::d4e8:fcff:febf:5937 > ff02::16: HBH ICMP6, multicast listener report v2, 2 group record(s), length 48
13:47:07.071788 IP6 fe80::d4e8:fcff:febf:5937 > ff02::16: HBH ICMP6, multicast listener report v2, 2 group record(s), length 48
13:47:07.423792 IP6 :: > ff02::1:ff00:300: ICMP6, neighbor solicitation, who has 2a01:4f8:221:3744:4000::300, length 32

dhcpd6 log

Apr 01 13:35:41 status.nixcloud.io dhcpd6[9225]: Copyright 2004-2016 Internet Systems Consortium.
Apr 01 13:35:41 status.nixcloud.io dhcpd6[9225]: All rights reserved.
Apr 01 13:35:41 status.nixcloud.io dhcpd6[9225]: For info, please visit https://www.isc.org/software/dhcp/
Apr 01 13:35:41 status.nixcloud.io dhcpd6[9225]: Wrote 0 NA, 0 TA, 0 PD leases to lease file.
Apr 01 13:35:41 status.nixcloud.io dhcpd[9225]: Wrote 0 NA, 0 TA, 0 PD leases to lease file.
Apr 01 13:35:42 status.nixcloud.io dhcpd6[9225]: Bound to *:547
Apr 01 13:35:42 status.nixcloud.io dhcpd[9225]: Bound to *:547
Apr 01 13:35:42 status.nixcloud.io dhcpd[9225]: Listening on Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Apr 01 13:35:42 status.nixcloud.io dhcpd[9225]: Sending on   Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Apr 01 13:35:42 status.nixcloud.io dhcpd6[9225]: Listening on Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Apr 01 13:35:42 status.nixcloud.io dhcpd6[9225]: Sending on   Socket/5/brNC-internet/2a01:4f8:221:3744:4000::/66
Apr 01 13:35:42 status.nixcloud.io systemd[1]: Started DHCPv6 server.
Apr 01 13:35:42 status.nixcloud.io dhcpd6[9227]: Server starting service.
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Solicit message from fe80::d4e8:fcff:febf:5937 port 546, transaction ID 0x693A9D00
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Picking pool address 2a01:4f8:221:3744:4000::300
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Advertise NA: address 2a01:4f8:221:3744:4000::300 to client with duid 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6 iaid = 1 valid for 86400 seconds
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Sending Advertise to fe80::d4e8:fcff:febf:5937 port 546
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Request message from fe80::d4e8:fcff:febf:5937 port 546, transaction ID 0x8694C500
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Reply NA: address 2a01:4f8:221:3744:4000::300 to client with duid 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6 iaid = 1 valid for 86400 seconds
Apr 01 13:44:47 status.nixcloud.io dhcpd6[9227]: Sending Reply to fe80::d4e8:fcff:febf:5937 port 546
Apr 01 13:45:38 status.nixcloud.io dhcpd6[9227]: Release message from fe80::d4e8:fcff:febf:5937 port 546, transaction ID 0x176D6200
Apr 01 13:45:38 status.nixcloud.io dhcpd6[9227]: Client 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6 releases address 2a01:4f8:221:3744:4000::300
Apr 01 13:45:38 status.nixcloud.io dhcpd6[9227]: Sending Reply to fe80::d4e8:fcff:febf:5937 port 546
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Solicit message from fe80::d4e8:fcff:febf:5937 port 546, transaction ID 0x9D658700
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Advertise NA: address 2a01:4f8:221:3744:4000::300 to client with duid 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6 iaid = 1 valid for 86400 seconds
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Sending Advertise to fe80::d4e8:fcff:febf:5937 port 546
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Request message from fe80::d4e8:fcff:febf:5937 port 546, transaction ID 0xBF064200
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Reply NA: address 2a01:4f8:221:3744:4000::300 to client with duid 00:01:00:01:22:52:a7:e3:0a:79:bb:c7:9c:d6 iaid = 1 valid for 86400 seconds
Apr 01 13:45:44 status.nixcloud.io dhcpd6[9227]: Sending Reply to fe80::d4e8:fcff:febf:5937 port 546
Apr 01 13:46:20 status.nixcloud.io dhcpd6[9227]: Unable to add forward map from 11.your.domain.com to 2a01:4f8:221:3744:4000::300: timed out

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