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I want to change my Ubuntu to static IP. My current IP setting is:

eth0      Link encap:Ethernet  HWaddr 00:0c:29:xx:xx:xx  
      inet addr:192.168.16.59  Bcast:192.168.31.255  Mask:255.255.240.0
      inet6 addr: fe80::20c:xx:xx:xx/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:234690 errors:0 dropped:0 overruns:0 frame:0
      TX packets:1864 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:22953435 (22.9 MB)  TX bytes:205616 (205.6 KB)

what should I put as the network in /etc/network/interfaces (note the network mask of 255.255.240.0)?

share|improve this question
    
What exactly do you have trouble with? I don't see any network statements in interfaces(5). You might consider rephrasing your question and add some details. – Andreas Wiese Mar 31 '14 at 19:56
1  
Stop using ifconfig, use ip addr instead. This is what ifupdown (the software that parses /etc/network/interfaces) uses under the hood anyway, so you will definitely want to get used to it. – BatchyX Mar 31 '14 at 20:06
    
@BatchyX, I use ip addr for other things but not this one, because it'd be worse that ifconfig -- ifconfig at least gives me address, broadcast & netmask, but ip addr doesn't give me netmask, at least my version doesn't. – xpt Apr 1 '14 at 2:40
    
@xpt: ip addr gives you the modern CIDR prefix length just next to the IP address. It also accept old-style netmask on input (i.e. 192.168.31.254/255.255.240.0) – BatchyX Apr 2 '14 at 17:52
up vote 1 down vote accepted

If I'm understanding your question, to set a static IP, your network runs from 191.168.16.1 - 191.168.31.254, with the identity address at 192.168.16.0 and the broadcast at 192.168.31.255. I've never had to use the Network keyword, but I've never used a supernet address on a host. I've only seen them used for route aggregation.

 auto eth0
 iface eth0 inet static
 address 192.168.16.59
 network 192.168.16.0
 netmask 255.255.240.0
 broadcast 192.168.31.255
 gateway 192.168.0.1
share|improve this answer
    
My IP is not a good example for network for this case. I guess if my IP is 192.168.18.159, my network value is still 192.168.16.0, correct? BTW, are you saying that is network optional for /etc/network/interfaces? I'm following guylabs.ch/2013/07/25/configure-a-static-ip-in-ubuntu-13-04, and there is a network there. – xpt Apr 1 '14 at 2:29
    
it depends on your network mask. for the Class C network 192.168.X.Y, a subnetted network would have >24 bits of mask (255.255.255.0-252), a supernetted net would have < 24 bits mask (255.0-255.0-252.0), and a normal (class natural) Class C would be 255.255.255.0. which one it is defines the "shape" of your IP address layout. – Frank Thomas Apr 1 '14 at 11:27
1  
yep. now that said, there is the possibility that subnetworks are defined under this address space, so make sure when configuring systems in this way that they all have a 255.255.240.0 mask. if you see any more confining masks (more than 20 bits) you will need to recalculate the network range, ID, and broadcast when configuring systems on that network. I use this calculator: subnet-calculator.com – Frank Thomas Apr 1 '14 at 14:16
2  
network is totally ignored by ifupdown, the system can figure it by itself anyway. Your broadcast is useless here: the system will pick the same in your case. Your gateway is not part of your subnet, so ifupdown will fail at that point. – BatchyX Apr 2 '14 at 18:00
1  
And nobody told you that classful addressing has been deprecated and dead for 20 years now ? All the Internet uses Classless interdomain routing now (CIDR for short, see RFC 4632), so there is no concept of "classes" or "supernetting" anymore. You may even specify a prefix length in netmask (like netmask 20) instead of a netmask. – BatchyX Apr 2 '14 at 18:08

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