# How can I get the local machine's netmask programmatically? **URL:** \ **Category:** Ruby\ **Created:** [June 13, 2007, 10:31pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765 "2007-06-13T22:31:32Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 13, 2007, 10:31pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/1 "2007-06-13T22:31:32Z")
I’m working on a Rails app that needs to restrict certain privileged operations/requests to only those requests that originate from within the local subnet. How can I find out the machine’s netmask programmatically? Thanks, Wolf ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 13, 2007, 11:13pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/2 "2007-06-13T23:13:38Z")
On 6/13/07, wolfram [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’m working on a Rails app that needs to restrict certain privileged > operations/requests to only those requests that originate from within > the local subnet. > > How can I find out the machine’s netmask programmatically? Hi, what operating system? windows/linux(distribution?)/osx? how many network adapters are in the machine? on windows use `ipconfig /all` and parse output or WMI through Win32OLE on unix `/sbin/ifconfig -a` If there are more adapters, you have to choose the right one (or allow all local nets). J. ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 12:45am UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/3 "2007-06-14T00:45:52Z")
> what operating system? windows/linux(distribution?)/osx? > how many network adapters are in the machine? Linux. > on windows use `ipconfig /all` and parse output or WMI through Win32OLE > on unix `/sbin/ifconfig -a` I know about the system commands. Is there a library/API to get these programmatically without having to parse output from a sytem command? Thanks, W. ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 1:30am UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/4 "2007-06-14T01:30:58Z")
On Thu, 2007-06-14 at 07:45 +0900, wolfram wrote: > Thanks, > W. Create a socket and pull it from the socket structure. ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 6:49pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/5 "2007-06-14T18:49:48Z")
I spent quite a bit of time last night trying to figure this out to no avail. Reid, how long did it take you to come up with this? Could anyone without C experience figured this out? ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 3:19am UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/6 "2007-06-14T03:19:09Z")
On Thu, 2007-06-14 at 08:30 +0900, Reid T. wrote: > > programmatically without having to parse output from a sytem command? > > > > Thanks, > > W. > > Create a socket and pull it from the socket structure. see if this works…??? rthompso@shienar ~ $ cat getnetmask.rb require ‘rubygems’ require “inline” class NetMask inline do |builder| builder.include ‘\’ builder.include ‘\’ builder.include ‘\’ builder.include ‘\’ builder.include ‘\’ builder.c " ``` char * nmask() { int fd; struct ifreq ifr; fd = socket(AF_INET, SOCK_DGRAM, 0); ifr.ifr_addr.sa_family = AF_INET; strncpy(ifr.ifr_name, \"eth0\", IFNAMSIZ-1); ioctl(fd, SIOCGIFNETMASK, &ifr); close(fd); return (char *)inet_ntoa(((struct sockaddr_in ``` \*)&ifr.ifr\_addr)-\>sin\_addr); }" end end nm = NetMask.new() nmaa = nm.nmask() puts nmaa rthompso@shienar ~ $ ruby getnetmask.rb 255.255.255.0 ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 7:44pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/7 "2007-06-14T19:44:23Z")
On Fri, 2007-06-15 at 01:48 +0900, removed\_email\_address@domain.invalid wrote: > > > > > how many network adapters are in the machine? > > > > > W. > > > > > inline do |builder| > > > > nm = NetMask.new() > > nmaa = nm.nmask() > > puts nmaa > > > > rthompso@shienar ~ $ ruby getnetmask.rb > > 255.255.255.0 [http://www.hashcode.eti.br/?p=46](http://www.hashcode.eti.br/?p=46) makes an interesting read also ---
**Author:** ![wolfram](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/e68b1a/32.png) [@wolfram](https://www.ruby-forum.com/u/wolfram)\ **Post date:** [June 14, 2007, 7:22pm UTC](https://www.ruby-forum.com/t/how-can-i-get-the-local-machines-netmask-programmatically/106765/8 "2007-06-14T19:22:53Z")
On Fri, 2007-06-15 at 01:48 +0900, removed\_email\_address@domain.invalid wrote: > > require ‘rubygems’ > > > > ``` > > return (char *)inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr); > > > > ``` 1. I was previously aware of RubyInline – so didn’t have to ‘find/research’ it 2. I knew that getting the info in C code was doable 3. I googled for examples of getting socket info 4. it took me about 15 minutes probably 4a) I think a non-C programmer could have figured it out in time I basically copied the C RubyInline example ( the factorial one ) and pasted in the socket code. The gotcha’s would probably have been a)figuring out to use the builder.include, described in the C++ example, to get the header files included b)getting rid of a warning message due to the original C code not casting to (char \*) the return value of inet\_ntoa() 1. Ruby’s various socket classes probably provide access to the same info - but I couldn’t find out how to get at it ( like you, I spent waaaay more time trying to find a pure ruby way of getting the info than coding the example ) i.e. Ruby’s Socket class has a getsockname which returns the struct sockaddr packed into a string – It may have all the info needed, but I’m not familiar enough with unpacking a sockaddr structure to try to figure it out ( or unpacking anything in Ruby for that matter 🙂 ).