CIDR: A Prescription for Shortness of Address Space
Another way many companies can expand their pool of usable IP addresses is to take advantage of the private IP addresses set aside for companies and individuals not requiring direct Internet access on all their machines. These numbers can be used as seen fit.
By using a firewall or proxy server that performs network address translation (NAT), called “masquerading” in the Linux community, these machines can still connect to the Internet. The bright side is you won't be routing internal company addresses to the Internet, since most routers are set up to not route these private addresses. Conversely, no one can directly access your systems, so rogue web sites springing up in your company will not come back to haunt you. In order for anyone to access an internal computer, they would have to either log in to the proxy server first, then continue in, or be redirected by the proxy through the server to the designated machine.
The reference for those addresses we can make use of with no prior coordination is RFC 1918, “Address Allocation for Private Internets”, February 1996. These private addresses are as follows (excerpt from RFC):
10.0.0.0 - 10.255.255.255 (10/8 prefix) 172.16.0.0 - 172.31.255.255 (172.16/12 prefix) 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
Note that under the old classful addressing, while the first address segment is one Class A network, the second would actually be 16 Class B networks, and the final segment 256 Class C networks. By implementing a Linux gateway box and setting up some simple rules in ipfwadm (generally available with all Linux distributions), we can perform masquerading or Network Address Translation, giving all computers on the private network full Internet access. However, those on the Internet cannot get to any of the computers with private addresses unless one of two things happens. One, the administrator sets up the gateway to act as a proxy server; proxying requests on a particular port to a particular computer, or two, by the Internet user using TELNET to access the gateway box first, then on to the internal computers. Thus, private addresses stay private.
These address groups can also be put to use in private networks that piggy back on the Internet. By using two “live” (non-private) IP addresses, one on each network's “gateway” machine, we can tie two private networks together using Linux's IPIP, IP tunneled inside IP. While this won't provide privacy unless the two gateways are running an encryption program such as ssh (secure shell), it can provide a virtual network.
While live Internet addresses are becoming scarce, companies and individuals can maximize use of their current address space and even expand their address space through the use of private addresses. CIDR can also be used to improve security and increase network response time through subnetting.
By staying current with trends in such things as CIDR and Linux's networking software, most obstacles to Internet and Intranet connectivity can be easily circumvented. As CIDR provides everyone with a way to maximize the little we have, private addresses afford us the flexibility to expand beyond those addresses provided by our Internet Service Provider.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide