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. Subnet mask and netmask are the same thing. 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. To easily describe netmasks, I usually just say they tell you how big the network is you're referring to. 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>-------- Original message --------</div><div>From: tclug at freakzilla.com </div><div>Date:02/03/2015 4:56 AM (GMT-06:00) </div><div>To: TCLUG <tclug-list at mn-linux.org> </div><div>Subject: Re: [tclug-list] The cleaner: </div><div> </div>First - you see, Paul, you ask good questions, you get good answers. SIMPLE SIMPLE TL;DR version: it's the scope of the network. 127.0.0.1/8 means "ok, 127.anything is local, so I don't need to look for routes on how to get there." Something like 192.168.100.20/24 says "Ok, anything on 192.168.100.* is on the local network, so I don't need to find special ways to route that." But (barring other network rules) if it sees, say, 192.168.101.*, it will know it's an external network and try to figure out how to get there. LONGER AND MORE COMPLEX BUT STILL INCREDIBLY SIMPLIFIED version: You'll nitice an IP address (with IPv4 anyway) is divided into four numbers. We'll use 192.168.100.20. Each of these is called an octet but that's not important right now. Well, kinda. Now obviously every machine directly on the internet needs an address, and they had to be divided up somehow, and that's where subnets come in. There are three different sizes (or classes) of subnets. Class A, the biggest, is basically an entire subnet using the first octet. So, the Class A Subnet of 192.168.100.20 is 192.0.0.0 - so everything starting with 192.whatever. Since we're limited to numbers between 0 and 255, there is a limited number of Class A subnets, and we'll just say it's 255 even though it's not to keep it simple. Now, the Class B subnet uses the first two octets, so in this case it's 192.168.0.0. So every Class A subnet has 255 Class B subnets in it. Class C is 192.168.20.9, so every Class B has 255 Class C subnets. And every Class C has 255 individual IP addresses in it (again, it's not really 255 but we're keeping it simple). (How these got divided among different organisations is a long and arduous story. There are very few organisations that have a whole Class A to themselves, slightly more that have Class Bs, and many more have Class Cs, and a bunch of people share Class C subnets). Now, that number you're seeing after the / indicates what portion of the subnet an IP address is using. It's basically telling you the subnet mask, which is like the "negative" of the subnet, and is used for routing. The subnet mask for a Class A is 255.0.0.0, Class B is 255.255.0.0, and Class C is 255.255.255.0. Since you're normally running on a Class C, most your machines will have a subnet mask of 255.255.255.0. Now in the-number-after-the-slash terms, that's /24. So rather than saying: IP Address 192.168.100.20 Subnet Mask 255.255.255.0, you can just say 192.168.100.20/24 Now NARROWER subnet masks are not something you'll be using at home. They are used to divide networks up even more. For example, if you want to divide a Class C in two, you'd set the netmask to 255.255.255.128, and in / terms thats /25. Divide it in four, so you have fur networks of 64 IP addresses, and that's /26 (or 255.255.255.64). On Tue, 3 Feb 2015, paul g wrote: > Thank you: > > paul at desk/paul-Lenovo ~ $ ip addr | grep inet > inet 127.0.0.1/8 scope host lo > > Since I am on the topic what is the 127.0.0.1/8 meaning the /8 must mean > something right? If I can please ask your knowledge on this? > > I thank you for your time, > > - - > paul g > > > Date: Tue, 3 Feb 2015 04:20:44 -0600 > > From: tclug at freakzilla.com > > To: tclug-list at mn-linux.org > > Subject: Re: [tclug-list] The cleaner: > > > > On Tue, 3 Feb 2015, paul g wrote: > > > > > 1. what do/does the line's above labeled 'scope' refer to? I understand > that > > > I am not using ipv6 at this point in time. > > > > "scope host" means that address is only visible to and from that specific > > host. Basically the the ip address "127.0.0.1" (also known as "localhost") > > can only be accessed from that specific host. On every UNIX machine, > > 127.0.0.1 is "this machine I am currently on". You ssh to 127.0.0.1 and > > the machine you're on will answer. It's basically it's address for itself. > > > > "scope link", I assume, would mean anything on that link can access it. > > And "global" would mean it's available globally on your network - but > > since that's a 192.168.* address it's only available on YOUR netwrok, and > > not the internet. > > > > _______________________________________________ > > TCLUG Mailing List - Minneapolis/St. Paul, Minnesota > > tclug-list at mn-linux.org > > http://mailman.mn-linux.org/mailman/listinfo/tclug-list > > _______________________________________________ TCLUG Mailing List - Minneapolis/St. Paul, Minnesota tclug-list at mn-linux.org http://mailman.mn-linux.org/mailman/listinfo/tclug-list -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20150203/03d8cd73/attachment-0001.html>