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 FREEBSD

nos-tun

NOS-TUN(8)						    BSD System Manager's Manual 						NOS-TUN(8)

NAME

     nos-tun -- implement ``nos'' or ``ka9q'' style IP over IP tunnel

SYNOPSIS

     nos-tun -t tunnel -s source -d destination -p protocol_number [source] target

DESCRIPTION

     The nos-tun utility is used to establish an nos style tunnel, (also known as ka9q or IP-IP tunnel) using a tun(4) kernel interface.

     Tunnel is the name of the tunnel device /dev/tun0 for example.

     Source and destination are the addresses used on the tunnel device.  If you configure the tunnel against a cisco router, use a netmask of
     ``255.255.255.252'' on the cisco.	This is because the tunnel is a point-to-point interface in the FreeBSD end, a concept cisco does not
     really implement.

     Protocol number sets tunnel mode.	Original KA9Q NOS uses 94 but many people use 4 on the worldwide backbone of ampr.org.

     Target is the address of the remote tunnel device, this must match the source address set on the remote end.

EXAMPLES

     This end, a FreeBSD box on address 192.168.59.34:

	   nos-tun -t /dev/tun0 -s 192.168.61.1 -d 192.168.61.2 192.168.56.45

     Remote cisco on address 192.168.56.45:

	   interface tunnel 0
	   ip address 192.168.61.2 255.255.255.252
	   tunnel mode nos
	   tunnel destination 192.168.59.34
	   tunnel source 192.168.56.45

AUTHORS

     Nickolay N. Dudorov <nnd@itfs.nsk.su> wrote the program, Poul-Henning Kamp <phk@FreeBSD.org> wrote the man-page.  Isao SEKI
     <iseki@gongon.com> added a new flag, IP protocol number.

BUGS

     We do not allow for setting our source address for multihomed machines.

BSD
								  April 11, 1998							       BSD

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LEARN ABOUT FREEBSD

nos-tun