sn domains

This page explains the encoding method of SN domains that have 8 characters.
Other form please refer to GGC.

SN domains are widely used in YouTube video cache servers. There are 8 significant characters which represent the servers' geographic location and serial number of server groups.

According to the domain list collected so far, the pattern is similar to 1e100.net.

Pattern

r1---sn-[123][45][6][78].googlevideo.com

Example

r1---sn-a5mekn7r.googlevideo.com

1. [123] represents city name, it's converted from IATA airport code. Read more at 1e100.net servers deployment geoinfo.

   Conversion rules

   • The 25 chars in the following box represent a-y respectively from left to right, top to bottom, i.e, 5 is for a, t is for y.
   • Note that the char in the bottom left corner is 0, not 1.
   • Besides, 1 is for z.

   It's a form of Substitution Cipher, the tableau can be get by 90 degree counter-clockwise rotation of alphanumeric table.

   According to the rules, a5m in the example above can be reverse converted to lax, it's Los Angeles.

   | 6 d k r y |
   | --------- |
   | 5 c j q x |
   | 4 b i p w |
   | 3 a h o v |
   | 2 9 g n u |
   | 0 8 f m t |
   | --------- |
   |   7 e l s | z
   

   Writing in code:

   table = '1023456789abcdefghijklmnopqrstuvwxyz'
   def iata2sn(iata):
       global table
       sn = ''
       for v in iata:
           i = ((ord(v) - ord('a')) * 7 + 5) % 36
           sn += table[i]
       return sn

   Reverse conversion:

   table = '1023456789abcdefghijklmnopqrstuvwxyz'
   def sn2iata(sn):
       global table
       iata = ''
       for v in sn:
           i = table.index(v)
           i = (5 - i % 7) * 5 + i / 7 + 10
           iata += table[i]
       return iata

2. [45] and [78] are combinations of first column's 10 chars in the table below. They represent the servers' group (Point of Presence) numbers. It's 0-9 from top to bottom respectively.

     | 1 2 3 4 5 6
   7 | 8 9 a b c d
   e | f g h i j k
   l | m n o p q r
   s | t u v w x y
   z | 0 1 2 3 4 5
   6 | 7 8 9 a b c
   d | e f g h i j
   k | l m n o p q
   r | s t u v w x
   y | z
   

   So, ek and 7r in the example can be reverse converted to 17 and 08.

   00-39:

      7e 7l 7s 7z 76 7d 7k 7r 7y
   e7 ee el es ez e6 ed ek er ey
   l7 le ll ls lz l6 ld lk lr ly
   s7 se sl ss sz    sd sk sr
   

   7e represents 01, el is for 12, s7 is for 30, etc.

   Writing in code:

   table = '1023456789abcdefghijklmnopqrstuvwxyz'
   def num2code(num):
       global table
       code = ''
       for v in num:
           i = ((ord(v) - ord('0') + 1) * 7) % 36
           code += table[i]
       return code

3. [6] in the SN domain is n or u for IPv6, it's m for IPv4.

   The range of 49-64 bits in n's corresponding IPv6 addresses is 0 - 3ff.
   The range of 49-64 bits in u's corresponding IPv6 addresses is 400 - 7ff.
   (Read more about the IPv6 address allocation rules at Google.)

   e.g.

   • a5mekn7r, IPv6 prefix is 2607:f8b0:4007:a::/64, IPv4 prefix is74.125.103.0/24.
   • a5m7zu7r, IPv6 prefix is 2607:f8b0:4007:407::/64, IPv4 prefix is 74.125.215.0/24.
   • a5mekm76, no IPv6, IPv4 prefix is 208.117.242.0/24.

   a5m can be reverse converted to lax, so all of three SN domains above belong to Los Angeles.

• We can convert lax17s08 of 1e100.net style to a5mekn7r of SN domains style.
• See conversion code.
• See all SN domains.