<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body >Depending on how semantically accurate you want to be, using the "class" based nomenclature is generally not appropriate. I realize the classes are now generally the modern day equivalent to /8, /16, and /24 but it still irks me in a pet peeve kind of way. The classes referred to specific subsets of addresses of a particular net size, not just net sizes alone. Not only that but people usually don't include Multicast class D which is also actively used. The class E addresses are basically defunct. <div><br></div><div>Subnet mask and netmask are the same thing. </div><div>The "/#" notation, aka slash notation, is a shorthand for the netmask in decimal cidr representation where the number after the slash is the number of bits used to represent the network portion/size for the address in question. In IPv6 addressing slash notation is used exclusively instead of being spelled out in hexadecimal format because the addresses are already so long. </div><div><br></div><div>To easily describe netmasks, I usually just say they tell you how big the network is you're referring to. </div><div><br></div><div><br></div><div>By the way a 64 block (/26) has a decimal netmask of 255.255.255.192 which was accidentally listed as 255.255.255.64</div><div><br></div><br><br><div>-------- Original message --------</div><div>From: tclug@freakzilla.com </div><div>Date:02/03/2015 4:56 AM (GMT-06:00) </div><div>To: TCLUG <tclug-list@mn-linux.org> </div><div>Subject: Re: [tclug-list] The cleaner: </div><div><br></div>First - you see, Paul, you ask good questions, you get good answers.<br><br><br>SIMPLE SIMPLE TL;DR version: it's the scope of the network.<br><br>127.0.0.1/8 means "ok, 127.anything is local, so I don't need to look for <br>routes on how to get there."<br><br>Something like 192.168.100.20/24 says "Ok, anything on 192.168.100.* is on <br>the local network, so I don't need to find special ways to route that." <br>But (barring other network rules) if it sees, say, 192.168.101.*, it will <br>know it's an external network and try to figure out how to get there.<br><br><br><br>LONGER AND MORE COMPLEX BUT STILL INCREDIBLY SIMPLIFIED version:<br><br><br>You'll nitice an IP address (with IPv4 anyway) is divided into four <br>numbers. We'll use 192.168.100.20. Each of these is called an octet but <br>that's not important right now. Well, kinda.<br><br>Now obviously every machine directly on the internet needs an address, and <br>they had to be divided up somehow, and that's where subnets come in.<br><br>There are three different sizes (or classes) of subnets. Class A, the <br>biggest, is basically an entire subnet using the first octet. So, the <br>Class A Subnet of 192.168.100.20 is 192.0.0.0 - so everything starting <br>with 192.whatever. Since we're limited to numbers between 0 and 255, there <br>is a limited number of Class A subnets, and we'll just say it's 255 even <br>though it's not to keep it simple.<br><br>Now, the Class B subnet uses the first two octets, so in this case it's <br>192.168.0.0. So every Class A subnet has 255 Class B subnets in it.<br><br>Class C is 192.168.20.9, so every Class B has 255 Class C subnets.<br><br>And every Class C has 255 individual IP addresses in it (again, it's not <br>really 255 but we're keeping it simple).<br><br>(How these got divided among different organisations is a long and arduous <br>story. There are very few organisations that have a whole Class A to <br>themselves, slightly more that have Class Bs, and many more have Class Cs, <br>and a bunch of people share Class C subnets).<br><br>Now, that number you're seeing after the / indicates what portion of the <br>subnet an IP address is using. It's basically telling you the subnet mask, <br>which is like the "negative" of the subnet, and is used for routing. The <br>subnet mask for a Class A is 255.0.0.0, Class B is 255.255.0.0, and Class <br>C is 255.255.255.0. Since you're normally running on a Class C, most your <br>machines will have a subnet mask of 255.255.255.0.<br><br>Now in the-number-after-the-slash terms, that's /24. So rather than <br>saying:<br><br>IP Address 192.168.100.20 Subnet Mask 255.255.255.0, you can just say <br>192.168.100.20/24<br><br>Now NARROWER subnet masks are not something you'll be using at home. They <br>are used to divide networks up even more. For example, if you want to <br>divide a Class C in two, you'd set the netmask to 255.255.255.128, and in <br>/ terms thats /25. Divide it in four, so you have fur networks of 64 IP <br>addresses, and that's /26 (or 255.255.255.64).<br><br><br><br>On Tue, 3 Feb 2015, paul g wrote:<br><br>> Thank you:<br>> <br>> paul@desk/paul-Lenovo ~ $ ip addr | grep inet<br>> inet 127.0.0.1/8 scope host lo<br>> <br>> Since I am on the topic what is the 127.0.0.1/8 meaning the /8 must mean<br>> something right? If I can please ask your knowledge on this?<br>> <br>> I thank you for your time,<br>> <br>> - -<br>> paul g<br>> <br>> > Date: Tue, 3 Feb 2015 04:20:44 -0600<br>> > From: tclug@freakzilla.com<br>> > To: tclug-list@mn-linux.org<br>> > Subject: Re: [tclug-list] The cleaner:<br>> ><br>> > On Tue, 3 Feb 2015, paul g wrote:<br>> ><br>> > > 1. what do/does the line's above labeled 'scope' refer to? I understand<br>> that<br>> > > I am not using ipv6 at this point in time.<br>> ><br>> > "scope host" means that address is only visible to and from that specific<br>> > host. Basically the the ip address "127.0.0.1" (also known as "localhost")<br>> > can only be accessed from that specific host. On every UNIX machine,<br>> > 127.0.0.1 is "this machine I am currently on". You ssh to 127.0.0.1 and<br>> > the machine you're on will answer. It's basically it's address for itself.<br>> ><br>> > "scope link", I assume, would mean anything on that link can access it.<br>> > And "global" would mean it's available globally on your network - but<br>> > since that's a 192.168.* address it's only available on YOUR netwrok, and<br>> > not the internet.<br>> ><br>> > _______________________________________________<br>> > TCLUG Mailing List - Minneapolis/St. Paul, Minnesota<br>> > tclug-list@mn-linux.org<br>> > http://mailman.mn-linux.org/mailman/listinfo/tclug-list<br>> <br>><br>_______________________________________________<br>TCLUG Mailing List - Minneapolis/St. Paul, Minnesota<br>tclug-list@mn-linux.org<br>http://mailman.mn-linux.org/mailman/listinfo/tclug-list<br></body>