Photo Roll from Hokkaido

Former Ministry From Edo Era in Goryokaku
Lat N 41 47.813 Long E 140 45.430
Fireworks “Hanabi” at Toya Lake
Lat N 42 33.970 Long E 140 49.228
f/16 30” ISO 640
Sapporo Subway O-dori Station, Exit to West-3 Intersection
Lat N 43 03.648 Long 141 21.118
Hakodate Bay Night View from Hakodate Mountain Observatory
Lat N 41 45.562 Long E 140 42.278
f/10 10” ISO 100

A Note on SIT Tunnel at Home

This blog article records the progress of setting up IPv6 tunnel to Hurricane Electric at home where my ISP has no plan in sight to provide prefix-delegated IPv6 access over a PPPoE.

Shorthands and Assumptions in This Note

  • eth0 connects to the Internet via IPv4. This note shall also apply to encapsulated interfaces, e.g. vlan15@eth0, lte0 or pppoe0.
  • eth1 connects to local LAN. Similar as above, the process shall be the same when LAN side is a VLAN or bridge (or both).
  • tun0 denotes the sit tunnel interface created in this step.
  • A line beginning with # denotes comments in the configuration notes.

Setting up the Tunnel Interface on ER-X

If registered correctly on TunnelBroker, it should provide the following information:

  • Logical address at local endpoint, e.g. 2001:444:111:222::2/64
  • Logical address at remote endpoint, e.g. 2001:444:111:222::1/64
  • IPv4 address at remote endpoint where encapsulated traffic is sent, e.g., the HE tunneling endpoint in Paris.
  • A routable prefix for client side delegation, e.g. 2001:444:112:222::/64. This is usually different from the v6 addresses for the endpoint, and HE will show segments of the prefix in bold.

Now fill ER-X configuration nodes with corresponding information and default routing for IPv6:

            address: [Fill logical v6 address in CIDR at endpoint]
            description: [Give a name to this tun]
            encapsulation: sit
            local-ip: [Fill in IPv4 address at eth0]
            remote-ip: [Fill in IPv4 address at tunneling endpoint]
                next-hop-interface: tun0
            # This creates a default IPv6 routing table entry that
            # routes all non-link-local address to the tunnel.

At this point, one should be able to ping any IPv6 address from the ER-X. If this is working, continue to instruct the LAN interface to delegate the prefix

            dup-addr-detect-transmits: 1
            # Stateless SLAAC configuration might produce identical
            # IP addresses. This allow the network to detect whether
            # a stateless address already exists.
                # Set autoconf to allow stateless delegation by SLAAC
                    [Fill routable delegated prefix here]:
                        autonomous-flag: true
                        # Instructs computers on this network to auto
                        # discover DNS servers
                        on-link-flag: true
                        # Indicates that this prefix exists on the
                        # same Ethernet link, i.e. these addresses
                        # does not require routing

IPv6 enabled devices shall now receive globally unique IPv6 address assigned via SLAAC and prefix delegation.

Subsequent Steps

  • Confirm IPv6 assignment on LAN devices
$ ip addr
2: eno1:  mtu 1480 qdisc fq_codel state UP group default qlen 1000
     link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
     inet brd scope global dynamic noprefixroute eno1
        valid_lft 80444sec preferred_lft 80444sec
     inet6 2001:470:d:XXXX:XXXX:XXXX:XXXX:dfd3/64 scope global dynamic noprefixroute 
        valid_lft 2591976sec preferred_lft 86376sec
     inet6 fe80::be40:XXXX:XXXX:XXXX/64 scope link noprefixroute 
        valid_lft forever preferred_lft forever
  • Trace IPv6 connections to an IPv6 enabled website
$ traceroute -6 -n
 traceroute to (2606:4700:30::681c:1b16), 30 hops max, 80 byte packets
  1  2001:470:d:XXXX:XXXX:XXXX:XXXX:XXXX  0.415 ms  0.533 ms  0.624 ms
  2  2001:470:c:XXXX::1  185.353 ms *  203.802 ms
  3  2001:470:0:9d::1  178.603 ms  167.001 ms  189.255 ms
  4  2001:504:0:3:0:1:3335:1  196.520 ms  179.737 ms  196.117 ms
  5  2400:cb00:12:1024::6ca2:d61d  185.036 ms 2400:cb00:12:1024::6ca2:d614  175.573 ms 2400:cb00:12:1024::6ca2:d608  185.263 ms
  • It is advisable to setup network wide firewall on the router, as addresses can be reached by any other IPv6 connected devices from the Internet.

Further Notes

  • The sit tunnel shall also work if setup correctly on any other router or even a personal computer with public IPv4 address. I am unable to replicate the settings on a Linux router via raw commands as I do not own a linux machine with public IPv4 address.
  • I am not sure if the method would work if the local endpoint is behind NAT. This scenario will be experimented on after I return to campus.

“Certified” Androids?

The story begins with the moment I bought Cytus II on the very first day of its release from google play, expecting some real music gaming on my Surface Pro 3 running homebrew Android 7.1 (yes, that’s totally possible and it runs suprisingly fine with all hardware buttons and touchscreen working). However the game quits immediately and no logs are shown through the adb interface. I contacted Rayark for support and got reply like this:

Cytus II might only be compatible for native Android devices at the moment. Please also check if you have installed Xposed, firewalls, block ads, or any rooting software. If yes, these may effect the performance of the game. We’d like to suggest you to remove these software to ensure the game runs smoothly and properly.

(Probably) 3 weeks after the game’s release, I ended up playing Cytus II on my crammed 5′ mobile phone, not by choice though. Someone asked me, why I can’t buy a regular Android tablet or an iPad to do the same job. Well that could be an option if those people would donate in any means for a new one, and I really don’t think utilizing an existing hardware piece could cause any troubles for commercial devs and companies (Google: really?).

After some searches I reached conclusion that Cytus II has integrated an “compliance check” called SafetyNet and the underlying Compatibility Test Suite (CTS), a framework introduced by Google to verify if any android device falls into the category of “compatible”. Since Surface Pro 3 has never got an official Android release (it’s a Microsoft thing, of course) and the base android x86 is shipped with root and development mode on, there is probably no way that any CTS tests on Surface Pro 3 would pass any time sooner.

Just earlier this day, I saw the news that Google is attmpting to block Gapps from running on “uncertified” devices, where modding the android device or unlocking bootloader would void the “certified” status. There’s even a webpage letting people to “register” their Androids with their device identifier which is absolutely not working after I attempted to register my Surface only getting an unknown error.

I would not blame Rayark for their attempt to place a layer of piracy protection on such a nice game while hurting the ones who modded their devices properly exactly to play these games. My question is: If such a lockdown is so important that this system had been deployed to thousands of android software by now, why make android an open standard? Why not switch to the Apple production mode if a centralized control force seems so vital to the whole android community? Such blockage wouldn’t be easily tolerated if the so called “register uncertified devide page” is just a lie, and I believe there will be a solution to circumvent such unreasonable restrictions eventually. Before that, the vast population of “uncertified” androids and modders wouldn’t be so comfortable and I might really need to ask myself: Why I should spend 3 months porting an open source OS to a new device just to find nothing should works by design.

The Hot City?

When I told someone Chengdu is a hot city, I meant both food and the city itself. Hopefully, I finally remembered that I forgot procrastinated to post my photos I took when I travelled to Chengdu and stayed for a few days this winter. Still, these pictures are taken from my old Canon 50D DSLR and the mediocre lens.

Continue reading The Hot City?

The season of white (photo) album

It’s -30 degree celcius in Madison. It’s snowing. It’s the season of white album again.


Camera: Canon EOS 50D (a really old DSLR)
Lens: Canon EF-S 17-85mm f4-5.6 IS USM (yes, the very mediocre default)
Aperture: f/5.6
Exposure: 1/500
Location: In my room [precise location redacted]

[Errata] Windows upgrade to 1703 broke grub

What happened?

After windows upgrading itself to release 1703 aka. the creator update, Grub bootloader can no longer start and says error: unknown filesystem and dropped in to grub rescue shell. Windows boots up fine from firmware memu.


Manually doing hexediting just taught me another valuable lesson: @Windows has the worst upgrade handling.

— @cth451 July 28, 2017

  1. Prepare a USB linux live environment.
  2. Find the correct partition number, it might have been changed during upgrade.
  3. Look for grubx64.efi in your EFI system partition and use a hex editor to open it
  4. Search for /boot/grub and notice the (,gptN) where N is your original partition number for linux OS.
  5. Change N to the new parition number, save the file and reboot.


Before upgrade, my partition scheme was:

  • sda1 fat32: EFI system parition
  • sda2 ext4: Archlinux root filesystem
  • sda4 ntfs: Windows drive C
  • sda3 ext4: AOSC OS root filesystem

Partition numbers were not exactly in physical order of data, for I shrinked Archlinux to make room for Windows installation. However after upgrade, it became:

  • sda1 fat32: EFI system parition
  • sda2 ext4: Archlinux root filesystem
  • sda3: Windows drive C
  • sda4: Windows recovery environment
  • sda5: AOSC OS root filesystem

So what did windows do down there? It shrinked drive C and made a little recovery partition, then re-sorted the partition numbers. However grub bootloader looks for partitions by partition number. It tried parition 3 (which was a valid linux filesystem), but it’s an ntfs now.

This partition number is hardcoded into the bootloader efi image, so we need to manually hexedit it.

Lake superior and sunset

Lake Superior – Sugarloaf Cove

Position: 47°29’11″N 90°58’59″W

Cobblestone underwater. Taken on sugarloaf cove beach with waterproof Xperia Z5.
Cobblestone underwater on sugarloaf cove beach with waterproof Xperia Z5.

I took this photo with the waterproof Xperia upside down with camera underwater. Not exactly what I expected but still amazing enough to see colorful cobblestone underwater.

Colorful cobblestones on the beach of Lake Superior
Colorful cobblestones on the beach of Lake Superior

Yet another regular collection of colorful stone beach.

Lake Mille Lacs

Position: 46°10’52″N 93°43’42″W

Lake Mille Lacs, partially frozen. Taken on a trail 2m from the shore.
Lake Mille Lacs, partially frozen. Taken on a trail 2m from the shore.

This one is pretty off-road on the side of a trail beyond Indians point. Cold, but beautiful.

Minnesota Route 1

Sunset on MN-1 westbound
Sunset on MN-1 westbound

Unfortunately I lost Geo-tag in this photo… So I don’t know the precise location on the road.

Goodbye, chunky. Hi, Blender! (with the Interior Of Dat Triangle)

This would be one of my last frames of Minecraft renderworks with chunky. I will be switching to blender, an open source modeling software that supports GPU ray tracing with CUDA and allows tweaks to model before performing actual (now night-long) rendering.

Chunky is still pretty straightforward to newbie CG makers, written in java that virtually runs everywhere, but it does not support GPU rendering, and java multi-threading overhead made it even worse.

Blender, on the other hand, needs a few hours to setup but provides far more precise control over elements, vertices, edges and fancy stuff. Cropping down map portions out of the camera view, customize torch light color, removing specific blocks, render entities with actual motion…

So… Goodbyeさようなら, chunky. Hi, Blender!

I might still recommend chunky for those who want to have a sip of minecraft rendering, but for more complex terrain and huge creations, use blender.

Here’s the downscaled rendered frame, but you can still find full resolution on deviant art.

Rendering Specs:

Rendering time: 1.57 days
Threads: 3
Original dimensions: 4000x4000
Downscaled dimensions for uploading: 2000x2000