Mastodawn

🚀💻 Oh wow, you can now host a web service with zero ports exposed! Because nothing screams "cutting-edge tech" like skipping the 101 on network basics. 🙄🔒 Thanks, Erisa, for guiding us through this groundbreaking concept—next up, how to bake cookies without an oven! 🍪🔥
https://erisa.dev/exposing-a-web-service-with-cloudflare-tunnel/ #webservice #zeroports #cuttingedgetechnology #networkbasics #techinnovation #HackerNews #ngated

Exposing a web service with Cloudflare Tunnel

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Erisa's Corner of the Internet

OSTechNix Feb 27

Understanding Common Port Numbers: A Beginner's Guide to Networking #Portnumber #Port #Networking #Linux #Devops #NetworkBasics
https://ostechnix.com/understanding-common-port-numbers/

The Wiert Corner - irregular stream of stuff Nov 27, 2024

IPv4 subnet/CIDR table from OccupytheWeb on Twitter: “Network Basics for Hackers: Subnetting, Subnet Masks and CIDR Notation …”

I wrote about programs and scripts doing IPv4 subnet calculation, but sometimes it is easier to have a table at hand, so here is the one I found at [Wayback/Archive] OccupytheWeb on Twitter: “Network Basics for Hackers: Subnetting, Subnet Masks and CIDR Notation #networks #networkbasics #subnetting #infosec #networks4hackers #cyberwarrior #cyberwarrior #networkbasics #networkbasics subnet”

Notes:

it is by far original, as a quick image search revealed lots of other sources, for instance the 2011 post [Wayback/Archive] Subnet Mask Quick Reference | Academic PCs Blog
there is a much better table below adapted from Classless Inter-Domain Routing: IPv4 CIDR blocks – Wikipedia

Some earlier related posts:

And another example where the same table was used: [Wayback/Archive] tcpip – How to understand the “A subnet Example”? – Server Fault.

Since this one from Classless Inter-Domain Routing: IPv4 CIDR blocks – Wikipedia is much better, I copied it in full then colourised it using the above scheme and added the mask octet and binary mask columns, then added the “(max hosts)” to the “Decimal” columns:

IPv4 CIDR blocks

Address
formatDifference
to last addressMaskMask
octetBinary mask
in octetAddressesRelative
to class
A, B, CRestrictions
on a, b, c and d
(0..255 unless noted)Typical useDecimal
(max hosts)2na.b.c.d/32+0.0.0.0255.255.255.2554111111111201⁄256 CHost routea.b.c.d/31+0.0.0.1255.255.255.2544111111102211⁄128 Cd = 0 … (2n) … 254Point-to-point links (RFC 3021)a.b.c.d/30+0.0.0.3255.255.255.2524111111004221⁄64 Cd = 0 … (4n) … 252Point-to-point links (glue network)a.b.c.d/29+0.0.0.7255.255.255.2484111110008231⁄32 Cd = 0 … (8n) … 248Smallest multi-host networka.b.c.d/28+0.0.0.15255.255.255.24041111000016241⁄16 Cd = 0 … (16n) … 240Small LANa.b.c.d/27+0.0.0.31255.255.255.2244111000003225⅛ Cd = 0 … (32n) … 224a.b.c.d/26+0.0.0.63255.255.255.1924110000006426¼ Cd = 0, 64, 128, 192a.b.c.d/25+0.0.0.127255.255.255.12841000000012827½ Cd = 0, 128Large LANa.b.c.0/24+0.0.0.255255.255.255.0311111111256281 Ca.b.c.0/23+0.0.1.255255.255.254.0311111110512292 Cc = 0 … (2n) … 254a.b.c.0/22+0.0.3.255255.255.252.03111111001,0242104 Cc = 0 … (4n) … 252Small businessa.b.c.0/21+0.0.7.255255.255.248.03111110002,0482118 Cc = 0 … (8n) … 248Small ISP/ large businessa.b.c.0/20+0.0.15.255255.255.240.03111100004,09621216 Cc = 0 … (16n) … 240a.b.c.0/19+0.0.31.255255.255.224.03111000008,19221332 Cc = 0 … (32n) … 224ISP/ large businessa.b.c.0/18+0.0.63.255255.255.192.031100000016,38421464 Cc = 0, 64, 128, 192a.b.c.0/17+0.0.127.255255.255.128.031000000032,768215128 Cc = 0, 128a.b.0.0/16+0.0.255.255255.255.0.021111111165,536216256 C = Ba.b.0.0/15+0.1.255.255255.254.0.0211111110131,0722172 Bb = 0 … (2n) … 254a.b.0.0/14+0.3.255.255255.252.0.0211111100262,1442184 Bb = 0 … (4n) … 252a.b.0.0/13+0.7.255.255255.248.0.0211111000524,2882198 Bb = 0 … (8n) … 248a.b.0.0/12+0.15.255.255255.240.0.02111100001,048,57622016 Bb = 0 … (16n) … 240a.b.0.0/11+0.31.255.255255.224.0.02111000002,097,15222132 Bb = 0 … (32n) … 224a.b.0.0/10+0.63.255.255255.192.0.02110000004,194,30422264 Bb = 0, 64, 128, 192a.b.0.0/9+0.127.255.255255.128.0.02100000008,388,608223128 Bb = 0, 128a.0.0.0/8+0.255.255.255255.0.0.011111111116,777,216224256 B = ALargest IANA block allocationa.0.0.0/7+1.255.255.255254.0.0.011111111033,554,4322252 Aa = 0 … (2n) … 254a.0.0.0/6+3.255.255.255252.0.0.011111110067,108,8642264 Aa = 0 … (4n) … 252a.0.0.0/5+7.255.255.255248.0.0.0111111000134,217,7282278 Aa = 0 … (8n) … 248a.0.0.0/4+15.255.255.255240.0.0.0111110000268,435,45622816 Aa = 0 … (16n) … 240a.0.0.0/3+31.255.255.255224.0.0.0111100000536,870,91222932 Aa = 0 … (32n) … 224a.0.0.0/2+63.255.255.255192.0.0.01110000001,073,741,82423064 Aa = 0, 64, 128, 192a.0.0.0/1+127.255.255.255128.0.0.01100000002,147,483,648231128 Aa = 0, 1280.0.0.0/0+255.255.255.2550.0.0.00000000004,294,967,296232256 AEntire IPv4 Internet, default route.

If you want to modify the table even further, please fork https://gist.github.com/jpluimers/d2665ef16ed20ec9b8266bf154c56830

For now it is hosted as HTML page at https://gist.githack.com/jpluimers/d2665ef16ed20ec9b8266bf154c56830/raw/27cd4c0583771198c65e68f21ee9968c1af64827/IPv4-CIDR-blocks.html

I posted a bitmap of it at [Wayback/Archive] Jeroen Wiert Pluimers on Twitter: “@three_cube For now the HTML is served at …”

–jeroen

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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" class="wf-inactive"><head profile="http://gmpg.org/xfn/11"><body><h1>IPv4 CIDR blocks</h1><table class="wikitable" rules="all"><tbody><tr><th rowspan="2">Address format</th><th rowspan="2">Difference to last address</th><th rowspan="2">Mask</th><th rowspan="2">Mask octet</th><th rowspan="2">Binary mask in octet</th><th colspan="2">Addresses</th><th rowspan="2">Relative to class A, B, C</th><th rowspan="2">Restrictions on a, b, c and d (0..255 unless noted)</th><th rowspan="2">Typical use</th></tr><tr><th>Decimal (max hosts)</th><th bgcolor="lightgreen">2n</th></tr><tr bgcolor="lightyellow"><td>a.b.c.d/32</td><td>+0.0.0.0</td><td>255.255.255.255</td><td>4</td><td>11111111</td><td>1</td><td>20</td><td>1⁄256 C</td><td></td><td>Host route</td></tr><tr><td>a.b.c.d/31</td><td>+0.0.0.1</td><td>255.255.255.254</td><td>4</td><td>11111110</td><td>2</td><td bgcolor="lightgreen">21</td><td>1⁄128 C</td><td>d = 0 … (2n) … 254</td><td>Point-to-point links (<a class="mw-redirect" title="RFC (identifier)" href="https://en.wikipedia.org/wiki/RFC_(identifier)">RFC</a> <a class="external text" href="https://datatracker.ietf.org/doc/html/rfc3021" rel="nofollow">3021</a>)</td></tr><tr><td>a.b.c.d/30</td><td>+0.0.0.3</td><td>255.255.255.252</td><td>4</td><td>11111100</td><td>4</td><td bgcolor="lightgreen">22</td><td>1⁄64 C</td><td>d = 0 … (4n) … 252</td><td>Point-to-point links (glue network)</td></tr><tr><td>a.b.c.d/29</td><td>+0.0.0.7</td><td>255.255.255.248</td><td>4</td><td>11111000</td><td>8</td><td bgcolor="lightgreen">23</td><td>1⁄32 C</td><td>d = 0 … (8n) … 248</td><td>Smallest multi-host network</td></tr><tr><td>a.b.c.d/28</td><td>+0.0.0.15</td><td>255.255.255.240</td><td>4</td><td>11110000</td><td>16</td><td bgcolor="lightgreen">24</td><td>1⁄16 C</td><td>d = 0 … (16n) … 240</td><td rowspan="3">Small <a class="mw-redirect" title="LAN" href="https://en.wikipedia.org/wiki/LAN">LAN</a></td></tr><tr><td>a.b.c.d/27</td><td>+0.0.0.31</td><td>255.255.255.224</td><td>4</td><td>11100000</td><td>32</td><td bgcolor="lightgreen">25</td><td>⅛ C</td><td>d = 0 … (32n) … 224</td></tr><tr><td>a.b.c.d/26</td><td>+0.0.0.63</td><td>255.255.255.192</td><td>4</td><td>11000000</td><td>64</td><td bgcolor="lightgreen">26</td><td>¼ C</td><td>d = 0, 64, 128, 192</td></tr><tr><td>a.b.c.d/25</td><td>+0.0.0.127</td><td>255.255.255.128</td><td>4</td><td>10000000</td><td>128</td><td bgcolor="lightgreen">27</td><td>½ C</td><td>d = 0, 128</td><td rowspan="2">Large <a class="mw-redirect" title="LAN" href="https://en.wikipedia.org/wiki/LAN">LAN</a></td></tr><tr bgcolor="lightyellow"><td>a.b.c.0/24</td><td>+0.0.0.255</td><td>255.255.255.0</td><td>3</td><td>11111111</td><td>256</td><td>28</td><td>1 C</td><td></td></tr><tr><td>a.b.c.0/23</td><td>+0.0.1.255</td><td>255.255.254.0</td><td>3</td><td>11111110</td><td>512</td><td bgcolor="lightgreen">29</td><td>2 C</td><td>c = 0 … (2n) … 254</td><td></td></tr><tr><td>a.b.c.0/22</td><td>+0.0.3.255</td><td>255.255.252.0</td><td>3</td><td>11111100</td><td>1,024</td><td bgcolor="lightgreen">210</td><td>4 C</td><td>c = 0 … (4n) … 252</td><td>Small business</td></tr><tr><td>a.b.c.0/21</td><td>+0.0.7.255</td><td>255.255.248.0</td><td>3</td><td>11111000</td><td>2,048</td><td bgcolor="lightgreen">211</td><td>8 C</td><td>c = 0 … (8n) … 248</td><td rowspan="2">Small <a class="mw-redirect" title="ISP" href="https://en.wikipedia.org/wiki/ISP">ISP</a>/ large business</td></tr><tr><td>a.b.c.0/20</td><td>+0.0.15.255</td><td>255.255.240.0</td><td>3</td><td>11110000</td><td>4,096</td><td bgcolor="lightgreen">212</td><td>16 C</td><td>c = 0 … (16n) … 240</td></tr><tr><td>a.b.c.0/19</td><td>+0.0.31.255</td><td>255.255.224.0</td><td>3</td><td>11100000</td><td>8,192</td><td bgcolor="lightgreen">213</td><td>32 C</td><td>c = 0 … (32n) … 224</td><td rowspan="3"><a class="mw-redirect" title="ISP" href="https://en.wikipedia.org/wiki/ISP">ISP</a>/ large business</td></tr><tr><td>a.b.c.0/18</td><td>+0.0.63.255</td><td>255.255.192.0</td><td>3</td><td>11000000</td><td>16,384</td><td bgcolor="lightgreen">214</td><td>64 C</td><td>c = 0, 64, 128, 192</td></tr><tr><td>a.b.c.0/17</td><td>+0.0.127.255</td><td>255.255.128.0</td><td>3</td><td>10000000</td><td>32,768</td><td bgcolor="lightgreen">215</td><td>128 C</td><td>c = 0, 128</td></tr><tr bgcolor="lightyellow"><td>a.b.0.0/16</td><td>+0.0.255.255</td><td>255.255.0.0</td><td>2</td><td>11111111</td><td>65,536</td><td>216</td><td>256 C = B</td><td></td><td></td></tr><tr><td>a.b.0.0/15</td><td>+0.1.255.255</td><td>255.254.0.0</td><td>2</td><td>11111110</td><td>131,072</td><td bgcolor="lightgreen">217</td><td>2 B</td><td>b = 0 … (2n) … 254</td><td></td></tr><tr><td>a.b.0.0/14</td><td>+0.3.255.255</td><td>255.252.0.0</td><td>2</td><td>11111100</td><td>262,144</td><td bgcolor="lightgreen">218</td><td>4 B</td><td>b = 0 … (4n) … 252</td><td></td></tr><tr><td>a.b.0.0/13</td><td>+0.7.255.255</td><td>255.248.0.0</td><td>2</td><td>11111000</td><td>524,288</td><td bgcolor="lightgreen">219</td><td>8 B</td><td>b = 0 … (8n) … 248</td><td></td></tr><tr><td>a.b.0.0/12</td><td>+0.15.255.255</td><td>255.240.0.0</td><td>2</td><td>11110000</td><td>1,048,576</td><td bgcolor="lightgreen">220</td><td>16 B</td><td>b = 0 … (16n) … 240</td><td></td></tr><tr><td>a.b.0.0/11</td><td>+0.31.255.255</td><td>255.224.0.0</td><td>2</td><td>11100000</td><td>2,097,152</td><td bgcolor="lightgreen">221</td><td>32 B</td><td>b = 0 … (32n) … 224</td><td></td></tr><tr><td>a.b.0.0/10</td><td>+0.63.255.255</td><td>255.192.0.0</td><td>2</td><td>11000000</td><td>4,194,304</td><td bgcolor="lightgreen">222</td><td>64 B</td><td>b = 0, 64, 128, 192</td><td></td></tr><tr><td>a.b.0.0/9</td><td>+0.127.255.255</td><td>255.128.0.0</td><td>2</td><td>10000000</td><td>8,388,608</td><td bgcolor="lightgreen">223</td><td>128 B</td><td>b = 0, 128</td><td></td></tr><tr bgcolor="lightyellow"><td>a.0.0.0/8</td><td>+0.255.255.255</td><td>255.0.0.0</td><td>1</td><td>11111111</td><td>16,777,216</td><td>224</td><td>256 B = A</td><td></td><td>Largest <a title="Internet Assigned Numbers Authority" href="https://en.wikipedia.org/wiki/Internet_Assigned_Numbers_Authority">IANA</a> block allocation</td></tr><tr><td>a.0.0.0/7</td><td>+1.255.255.255</td><td>254.0.0.0</td><td>1</td><td>11111110</td><td>33,554,432</td><td bgcolor="lightgreen">225</td><td>2 A</td><td>a = 0 … (2n) … 254</td><td></td></tr><tr><td>a.0.0.0/6</td><td>+3.255.255.255</td><td>252.0.0.0</td><td>1</td><td>11111100</td><td>67,108,864</td><td bgcolor="lightgreen">226</td><td>4 A</td><td>a = 0 … (4n) … 252</td><td></td></tr><tr><td>a.0.0.0/5</td><td>+7.255.255.255</td><td>248.0.0.0</td><td>1</td><td>11111000</td><td>134,217,728</td><td bgcolor="lightgreen">227</td><td>8 A</td><td>a = 0 … (8n) … 248</td><td></td></tr><tr><td>a.0.0.0/4</td><td>+15.255.255.255</td><td>240.0.0.0</td><td>1</td><td>11110000</td><td>268,435,456</td><td bgcolor="lightgreen">228</td><td>16 A</td><td>a = 0 … (16n) … 240</td><td></td></tr><tr><td>a.0.0.0/3</td><td>+31.255.255.255</td><td>224.0.0.0</td><td>1</td><td>11100000</td><td>536,870,912</td><td bgcolor="lightgreen">229</td><td>32 A</td><td>a = 0 … (32n) … 224</td><td></td></tr><tr><td>a.0.0.0/2</td><td>+63.255.255.255</td><td>192.0.0.0</td><td>1</td><td>11000000</td><td>1,073,741,824</td><td bgcolor="lightgreen">230</td><td>64 A</td><td>a = 0, 64, 128, 192</td><td></td></tr><tr><td>a.0.0.0/1</td><td>+127.255.255.255</td><td>128.0.0.0</td><td>1</td><td>10000000</td><td>2,147,483,648</td><td bgcolor="lightgreen">231</td><td>128 A</td><td>a = 0, 128</td><td></td></tr><tr bgcolor="lightyellow"><td>0.0.0.0/0</td><td>+255.255.255.255</td><td>0.0.0.0</td><td>0</td><td>00000000</td><td>4,294,967,296</td><td>232</td><td>256 A</td><td></td><td>Entire IPv4 Internet, <a title="Default route" href="https://en.wikipedia.org/wiki/Default_route">default route</a>.</td></tr></tbody></table></body></html> view raw

IPv4-CIDR-blocks.html

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#cyberwarrior #infosec #networkbasics #networks #networks4hackers #subnetting