Thanks Kevin!! On 2015-08-31 21:20, Kevin Fries wrote: > I am so embarrassed, I crossed up my 1's and 0's in my original post. > Let me correct it now. > > 0... Is Class A. This is designed for the largest network providers. > The subnet mask is 255.0.0.0. IP addresses in this range will start > with a first octet less than 128. RFC 1918 reserves the 10.x.x.x > network as unusable on the public internet. > > 10... Is Class B. These were designed for large corps and ISPs. The > subnet mask is 255.255.0.0. IP addresses in this range will start > with a first octet between 128 and 191. RFC 1918 reserves addresses > 172.[16-31].x.x for private only use. > > 110... Is Class C. These were designed for most corporations and have > a subnet mask of 255.255.255.0. IP addresses in this range will have > a first octet between 192 and 223. 192.168.x.x again is reserved by > RFC 1918 for private use. > > 1110... Is Class D. This is for multi broadcast networks and there is > never used as a primary interface. You will often see these addresses > used for things like NTP (Network Time Protocol) in broadcast mode. > Addresses will have a first octet between 224 and 240. > > Finally, there is 1111... Which is the "for future use" Class E, which > never got used. > > The subnet mask originally had a spec that allowed "wholes" in it. So > according to the original spec, 255.240.255.0 could be a legit subnet > mask. But the practical use for such a config never materialized, and > most routers to this day still won't support it. So... All the ones > end up on the left side of the mask, and all the zeros end up on the > right. So a shorthand notation emerged called CIDR. In CIDR > notation, you simply use a slash and the number of ones. > > So, 255.256.255.0 = 11111111.11111111.11111111.00000000 counting the > ones and you get /24. > > The idea of an address and subnet mask are simple. Take your IP > address and write it in binary. Take your mask and write it in > binary. Doing a binary AND on the values gives you the Network > address. Not the mask and do a binary AND, and you have the host > address. A binary OR on the same values gives you the broadcast > address. > > Now to use all this fun info... > > If Machine-A (i.e. a desktop) wants to talk to Machine-B (i.e. a web > server) the Network addresses are compared and it they are the same, > an ARP broadcast is used to identify that MAC address of Machine-B if > it is not already known, so the machines can communicate directly with > each other. If they are on different networks, the request is > forwarded to your default gateway to be forwarded (aka routed) to it > destination. > > Now, if we use the standard Class C address (let's say 192.168.0.x/24) > we have 256 possible addresses. All 0's is reserved for the Network, > and all 1's is reserved for the Broadcast. So 254 can be used for > actual machines. But what if I need more than 254 addresses? Let's > say I am supporting a network with 800 machines. Now what? Well, > stealing one bit from the Network and giving it to the host would > allow me 510 addresses, and 2 Bits would give me 1022. So how do I > steal those bits? Simple, declare my mask as /22 or 255.255.252.0. > With this example you can see why CIDR notation has become so > popular... Easier math. But, at the end of the day... It all means the > same thing... It's all about the binary notation. > > Sorry for my gaff, should have tried to reply while loading the car > with groceries, lol > > Kevin > On Aug 31, 2015 9:22 PM, "David Demland" wrote: > >> I wrote this paper to help with my students when I am teaching >> Subnetting I >> hope that you might find this a different way to look at >> networking. >> >> David >> >> -----Original Message----- >> From: plug-discuss-bounces@lists.phxlinux.org >> [mailto:plug-discuss-bounces@lists.phxlinux.org] On Behalf Of >> parabellum7@yahoo.com >> Sent: Monday, August 31, 2015 3:25 PM >> To: plug-discuss@lists.phxlinux.org >> Subject: Re: Understanding IP class range. >> >>> Very nice Kenn!! >> >> Thanks! Good to revisit this stuff from time to time, rattle the >> old >> brain-box and make sure there's still something in there! :) >> >>> Ok so if I had 192.168.1.0/25 [1] the range would be 192.168.1.0 >> - >>> 192.168.1.127 >> >> Yes. >> >>> /26 would be 192.168.1.0 - 192.168.1.192 ? or is it 192.168.1.0 >> - >> 192.168.1.64 ? >> >> /26 would yield 192.168.1.0 - 192.168.1.63 >> >>> Not sure how to make a net mask out of 192.168.1.0/25 [1] - >> would it be >> 255.255.255.128? >> >> Yes >> >> The calculator Daniel provided is good: >> >> http://www.subnet-calculator.com/cidr.php [2] >> >> The one kitepilot provided is also nice because it illustrates the >> full >> binary. >> >> http://jodies.de/ipcalc [3] >> >> They're neet to play with and better than others I've seen. I've >> bookmarked >> both, thanks for sharing these resources. >> >> --Kenn >> >> --------------------------------------------------- >> PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org To >> subscribe, >> unsubscribe, or to change your mail settings: >> http://lists.phxlinux.org/mailman/listinfo/plug-discuss [4] >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com [5] >> Version: 2015.0.6086 / Virus Database: 4409/10551 - Release Date: >> 08/31/15 >> >> --------------------------------------------------- >> PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org >> To subscribe, unsubscribe, or to change your mail settings: >> http://lists.phxlinux.org/mailman/listinfo/plug-discuss [4] > > > Links: > ------ > [1] http://192.168.1.0/25 > [2] http://www.subnet-calculator.com/cidr.php > [3] http://jodies.de/ipcalc > [4] http://lists.phxlinux.org/mailman/listinfo/plug-discuss > [5] http://www.avg.com > > --------------------------------------------------- > PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org > To subscribe, unsubscribe, or to change your mail settings: > http://lists.phxlinux.org/mailman/listinfo/plug-discuss -- Keith Smith --------------------------------------------------- PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org To subscribe, unsubscribe, or to change your mail settings: http://lists.phxlinux.org/mailman/listinfo/plug-discuss