IPv6 Neighbor Discovery Responder for KVM VPS

I Want IPv6 for Docker

I'm playing with Docker these days, and I want IPv6 in my Docker containers. The best guide for enabling IPv6 in Docker is how to enable IPv6 for Docker containers on Ubuntu 18.04. The first method in that article assigns private IPv6 addresses to containers, and uses IPv6 NAT similar to how Docker handles IPv4 NAT. I quickly got it working, but I noticed an undesirable behavior: Network Address Translation (NAT) changes the source port number of outgoing UDP datagrams, even if there's a port forwarding rule for inbound traffic; consequently, a UDP flow with the same source and destination ports is being recognized as two separate flows.

$ docker exec nfd nfdc face show 262
    faceid=262
    remote=udp6://[2001:db8:f440:2:eb26:f0a9:4dc3:1]:6363
     local=udp6://[fd00:2001:db8:4d55:0:242:ac11:4]:6363
congestion={base-marking-interval=100ms default-threshold=65536B}
       mtu=1337
  counters={in={25i 4603d 2n 1179907B} out={11921i 14d 0n 1506905B}}
     flags={non-local permanent point-to-point congestion-marking}
$ docker exec nfd nfdc face show 270
    faceid=270
    remote=udp6://[2001:db8:f440:2:eb26:f0a9:4dc3:1]:1024
     local=udp6://[fd00:2001:db8:4d55:0:242:ac11:4]:6363
   expires=0s
congestion={base-marking-interval=100ms default-threshold=65536B}
       mtu=1337
  counters={in={11880i 0d 0n 1498032B} out={0i 4594d 0n 1175786B}}
     flags={non-local on-demand point-to-point congestion-marking}

The second method in that article allows every container to have a public IPv6 address. It avoids NAT and the problems that come with it, but requires the host to have a routed IPv6 subnet. However, routed IPv6 is hard to come by on KVM servers, because virtualization platform such as Virtualizor does not support routed IPv6 subnets, but can only provide on-link IPv6.

On-Link IPv6 vs Routed IPv6

Enable IPv4 Access in EUserv IPv6-only VS2-free

EUserv is a virtual private server (VPS) provider in Germany. Notably, they offer a container-based Linux server, VS2-free, free of charge. VS2-free comes with one 1GHz CPU core, 1GB memory, and 10GB storage. Although I already have more than enough servers to play with, who doesn't like some more computing resources for free?

There's one catch: the VS2-free is IPv6-only. It neither has a public IPv4 address, nor offers NAT-based IPv4 access. All you can have is a single /128 IPv6 address.

$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 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
546: eth0@if547: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether b2:77:4b:c0:eb:0b brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 2001:db8:6:1::6dae/128 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::5ed4:d66f:bd01:6936/64 scope link
       valid_lft forever preferred_lft forever

If I attempt to access an IPv4-only destination, a "Network is unreachable" error appears:

$ host lgger.nexusbytes.com
lgger.nexusbytes.com has address 46.4.199.225
$ ping -n -c 4 lgger.nexusbytes.com
connect: Network is unreachable

How to Select Default IPv6 Source Address for Outbound Traffic in OpenVZ 7

I bought a few Virtual Private Servers (VPS) on Black Friday, and have been busy setting them up. Nowadays, most VPS comes with an IPv6 subnet that contains millions of possible addresses. Initially, only one IPv6 address is assigned to the server, but the user can assign additional addresses as desired. Given that I plan to run multiple services within a server, I added a few more IPv6 addresses so that each service can have a unique IPv6 address.

One of my servers is using OpenVZ 7 virtualization technology, in which I installed Debian 10 operating system. Commonly, OpenVZ 7 uses virtual network device (venet) that does not have a MAC address. venet devices are not fully IPv6 compliant, but still works if you statically assign IPv6 addresses. Moreover, every IP address used in a container must be configured from the host node, because venet would drop ip-packets from the container with a source address, and in the container with the destination address, which is not corresponding to an ip-address of the container. Therefore, I must use the VPS control panel, in this case SolusVM, to assign IPv6 addresses to my server:

IPv6 Subnet management in SolusVM

In the Add IP section, the IPv6 subnet prefix 2001:db8:f1c1:8454:0964: is already shown. Notice that I am putting a colon (:) in front of the suffix 1337, so that they concatenate to the full address 2001:db8:f1c1:8454:0964::1337. Forgetting this colon would cause "Invalid Entry" error.

After making this change in the SolusVM control panel, the /etc/network/interface file on my server is updated automatically:

How to Select Default IPv6 Source Address for Outbound Traffic with Netplan

I bought a few Virtual Private Servers (VPS) on Black Friday, and have been busy setting them up. Nowadays, most VPS comes with an IPv6 subnet that contains millions of possible addresses. Initially, only one IPv6 address is assigned to the server, but the user can assign additional addresses as desired. Given that I plan to run multiple services within a server, I added a few more IPv6 addresses so that each service can have a unique IPv6 address.

One of my servers is using KVM virtualization technology, in which I installed Ubuntu 20.04 operating system manually from an ISO image. Unlike a template-based installation, an ISO-installed Ubuntu 20.04 system manages its networks using Netplan, a backend-agnostic network configuration utility that generates network configuration from YAML files. Most VPS control panels, including SolusVM and Virtualizer, are unable to generate the YAML files needed by Netplan. IPv4 works out of box via DHCP, but IPv6 has to be configured manually. To assign two IPv6 addresses to my server, I need to write the following in /etc/netplan/01-netcfg.yaml:

network:
  version: 2
  ethernets:
    ens3:
      dhcp4: true
      addresses:
        - 2001:db8:30fa:5877::1/64
        - 2001:db8:30fa:5877::beef/64
      routes:
        - to: ::/0
          via: 2001:db8:30fa::1
          on-link: true
      nameservers:
        addresses:
        - 2001:4860:4860::8888
        - 2606:4700:4700::1111

I intend to host my secret beef recipes on its unique IPv6 address 2001:db8:30fa:5877::beef, and use the other address 2001:db8:30fa:5877::1 for outbound traffic such as pings and traceroutes. However, I noticed that the wrong address is being selected for outgoing packets:

$ ping 2001:db8:57eb:8479::2

$ sudo tcpdump -n icmp6
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on venet0, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
00:44:48.704099 IP6 2001:db8:30fa:5877::beef > 2001:db8:57eb:8479::2: ICMP6, echo request, seq 1, length 64
00:44:48.704188 IP6 2001:db8:57eb:8479::2 > 2001:db8:30fa:5877::beef: ICMP6, echo reply, seq 1, length 64
00:44:49.704011 IP6 2001:db8:30fa:5877::beef > 2001:db8:57eb:8479::2: ICMP6, echo request, seq 2, length 64
00:44:49.704099 IP6 2001:db8:57eb:8479::2 > 2001:db8:30fa:5877::beef: ICMP6, echo reply, seq 2, length 64

My Experience at Hack Arizona 2016

Hack Arizona is the largest collegiate hackathon in southwestern United States. I attended Hack Arizona 2016 and had a great experience, and I want to share what I experienced during this event.

Why I didn't attend in 2015

I heard about Hack Arizona when it started in 2015, but I decided against attending last year because 37 sleepless hours is harmful for health and won't produce high quality project.

Many of my friends went in 2015, and they shared their experiences and showed me their projects. The situation sounds less scary than I imagined:

  • Although you are provided enough coffee and Red Bull energy drinks to stay up, you are permitted to leave and re-enter at anytime, and you can sleep in the venue as well.
  • There's free food, and it's not just pizza.
  • Projects aren't of poor quality.