Subnetting Post: 302993570

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Special Forums IP Networking Subnetting Post 302993570 by drysdalk on Saturday 11th of March 2017 07:41:05 AM

03-11-2017

Registered User

Hi,

Firstly, from just looking at a single IP, you can't tell how large the network it's a part of is. You need to know the netmask. So for example, if I had an IP of 192.168.1.10, that doesn't tell you anything at all about how large or small the network I'm a part of is.

But if I tell you the netmask - e.g. 192.168.1.10/24 or 192.168.1.10/255.255.255.0 - then you know it's part of a network of 256 addresses, running from 192.168.1.0 to 192.168.1.255.

If on the other hand I'd told you the netmask was 192.168.1.10/25 or 192.168.1.10/255.255.255.128 - then you'd know it was part of a network of 128 addresses going from 192.168.1.0 to 192.168.1.127.

And again, in every network, the very first address and the very last address are not usable for hosts, as they are reserved for other purposes.

You can also get plenty of other netmasks than the old simple Class A, B, C notation tells you. For instance I could just have easily told you my netmask was 192.168.1.10/28, in which case you'd then be able to calculate that the network I was a part of runs from 192.168.1.0 to 192.168.1.15, and conists of 16 IP addresses.

So just from looking at an IP you can't tell anything about the size of the network. And these days, there are far more netmasks and subnet sizes that are far more common than the old Class A/B/C notation.

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vlan-interfaces

VLAN-INTERFACES(5)						   File formats 						VLAN-INTERFACES(5)

NAME

       /etc/network/interfaces (vlan) - vlan extensions for the interfaces(5) file format

DESCRIPTION

       /etc/network/interfaces	contains  network  interface  configuration  information  for  the  ifup(8)  and ifdown(8) commands.  This manpage
       describes the vlan extensions to the standard interfaces(5) file format.

       Primary extensions exist to make and destroy vlan interfaces, secondary extensions exist for ipv4 interface manipulation which  are  gener-
       ally needed when using (a lot of) vlans.

VLAN CREATION

       Vlan  interface	definitions  exist  of the vlan interface name, and an optional 'raw-device' parameter.  Vlan interfaces are numbered 1 to
       4095.  You have the option to have interface names zero-padded to 4 numbers, or just the plain digits without leading zero.  The  following
       example shows four ways to create a vlan with id 1 on interface eth0.  They all result in different names.

	iface eth0.1 inet static
	    address 192.168.1.1
	    netmask 255.255.255.0

	iface vlan1 inet static
	    vlan-raw-device eth0
	    address 192.168.1.1
	    netmask 255.255.255.0

	iface eth0.0001 inet static
	    address 192.168.1.1
	    netmask 255.255.255.0

	iface vlan0001 inet static
	    vlan-raw-device eth0
	    address 192.168.1.1
	    netmask 255.255.255.0

	# We don't have br support out of the box
	iface br0.2 inet static
	    vlan-raw-device br0
	    address 192.168.1.1
	    netmask 255.255.255.0

	# Aliases are ignored
	iface br0.2:1 inet static
	    address 192.168.1.1
	    netmask 255.255.255.255

EXTRA IFACE OPTIONS

       Usually someone who uses vlans also wants to do some other manipulations with the ip stack or interface.

       vlan-raw-device devicename
	      Indicates the device to create the vlan on.  This is ignored when the devicename is part of the vlan interface name.

       ip-proxy-arp 0|1
	      Turn proxy-arp off or on for this specific interface.  This also works on plain ethernet like devices.

       ip-rp-filter 0|1|2
	      Set the return path filter for this specific interface.  This also works on plain ethernet like devices.

       hw-mac-address mac-address
	      This sets the mac address of the interface before bringing it up.  This works on any device that allows setting the hardware address
	      with the ip command.

AUTHOR

       This manpage was adapted from interfaces(5) by Ard van Breemen <ard@kwaak.net>

SEE ALSO

       vconfig(8) interfaces(5)

vlan								 September 30 2007						VLAN-INTERFACES(5)

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vlan-interfaces