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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LEARN ABOUT DEBIAN

oidentd_masq.conf

oidentd_masq.conf(5)						File Formats Manual					      oidentd_masq.conf(5)

NAME

       oidentd_masq.conf - oidentd IP masquerading/NAT configuration file.

DESCRIPTION

       If you are using IP masquerading or NAT, oidentd can optionally return a username for connections from other machines.  Support for this is
       specified by calling oidentd with the -m (or --masq) flag and by creating an /etc/oidentd_masq.conf file.

       oidentd can also forward requests for an IP masqueraded connection to the machine from which connection originates by way of the -f option.
       This  will  only  work if the host to which the connection is forwarded is running oidentd with the -P (proxy) flag, or if the host's ident
       daemon will return a valid reply regardless of the input supplied by and the address of the host requesting the info  (some  ident  daemons
       for windows do this, maybe others).

FORMAT

       <IP Address|Hostname>[/<Mask>] <Ident Response> <System Type>

       The  first  field  contains the IP address or the hostname of a machine that IP masquerades through the machine on which oidentd runs.  The
       mask parameter can be either a network mask or a mask in CIDR notation.	A mask of 24 is equivalent to  255.255.255.0,  a  mask	of  16	is
       equivalent to 255.255.0.0, etc.

       The second field specifies the reply that oidentd will return for lookups to the host matching the IP address specified in the first param-
       eter.

       The third field specifies the operating system the machine matching the first parameter is running.

EXAMPLES

       <Host>[/<Mask>]		<Ident Response>    <System Type>
       192.168.1.1		     someone		 UNIX
       192.168.1.2		     noone		 WINDOWS
       192.168.1.1/32		     user1		 UNIX
       192.168.1.0/24		     user3		 UNIX
       192.168.0.0/16		     user4		 UNIX
       somehost 		     user5		 UNIX
       192.168.1.0/255.255.255.0     user6		 UNIX

AUTHOR

       Ryan McCabe <ryan@numb.org>
       http://dev.ojnk.net

SEE ALSO

       oidentd(8) oidentd.conf(5)

version 2.0.8							    13 Jul 2003 					      oidentd_masq.conf(5)

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oidentd_masq.conf