General questions about IP addresses

[Chris C.]

Hello,

I recently set up a new ISP account with one static IP address.

I requested my IP address and it gave me the option of choosing
between a block of 4 addresses with one useable address and a block of
8 with 5 useable. Would you guys please explain what the difference
is between the two options?

They sent me via e-mail the following info:

Unusable Network IP
Router Ethernet IP
First Usable IP
Last Usable IP
Broadcast IP
Subnet Mask for all IPs

I'm clueless as to what all of these mean. Would you guys mind
telling me what I can do with these addresses? Sorry, I am a total
newbie to DSL and networking.

What is the purpose of unusable IPs and broadcast IPs? Can I use them
for VPN or do I use them to assign addresses to subnets?

Thanks!!

 

[Lanwench [MVP - Exchange]]

Hello,

I recently set up a new ISP account with one static IP address.

I requested my IP address and it gave me the option of choosing
between a block of 4 addresses with one useable address and a block of
8 with 5 useable. Would you guys please explain what the difference
is between the two options?

Well, how many public IPs do you need? If you need more than one, get the
block of 8 with 5 usable. If you do the former, you can have only one public
IP address, which may or may not suffice for your needs. How many servers
will you have, and what will they run?

For your internal network, everyone should be on a private IP - your
router/firewall will do NAT, and if you're running a Windows server, have it
do DHCP for the private range (i.e., 192.168.0.0, 172.30.1.0, etc)

 

[Phillip Windell]

Unusable Network IP
Router Ethernet IP
First Usable IP
Last Usable IP
Broadcast IP
Subnet Mask for all IPs

What is the purpose of unusable IPs and broadcast IPs? Can I use them
for VPN or do I use them to assign addresses to subnets?

There are two unusable IP#s per each subnet. The first IP# is always the
Network ID# and cannot be used for Hosts. The last IP# is always the
Broadcast Address and cannot be used for Hosts. all others are "usable".
Usually the second IP# is the Router IP#, but that is just "tradition",...no
one is going to come looking for you if you use one of the other IP#s for
the Router. The "so-called" Router IP# is still a usable IP#.

Also for your furthur enjoyment,...when splitting an address block into
subnets, the *entire* last subnet is unusable,...and subsequently must be
split into more smaller subnets to gain back at least part of the lost IP#s.
However if you split it into full blocks (zeros in the host portion of the
mask) the last subnet is perfectly usable,...in fact they are considered
full networks and not really "subnets",....although for simplicity's sake
most will still refer to them as "subnets" right along with the rest.

Sample of a subnet

Unusable Network IP 192.168.20.64
Router Ethernet IP 192.168.20.65
First Usable IP 192.168.20.66
Last Usable IP 192.168.20.126
Broadcast IP 192.168.20.127
Subnet Mask for all IPs 255.255.255.192

Sample of a full network

Unusable Network IP 192.168.5.0
Router Ethernet IP 192.168.5.1
First Usable IP 192.168.5.2
Last Usable IP 192.168.5.254
Broadcast IP 192.168.5.255
Subnet Mask for all IPs 255.255.255.0


The sample subnet above is actually the Second Subnet you get when splitting
the address block 192.168.20.x by using 255.255.255.192 as the mask.

 

[Jeff Cochran]

I recently set up a new ISP account with one static IP address.

I requested my IP address and it gave me the option of choosing
between a block of 4 addresses with one useable address and a block of
8 with 5 useable. Would you guys please explain what the difference
is between the two options?

Four usable IP addresses, unless math has changed since I was in grade
school.

They sent me via e-mail the following info:

Unusable Network IP

The first address of a network block is not usable. Neither is the
last in the range since it's used fro broadcasts across the entire
network range.

Router Ethernet IP

This is actually usable, it just happesn to be used by the router to
get you to the ISP.

First Usable IP
Last Usable IP
Broadcast IP

As above.

Subnet Mask for all IPs

The subnet mask is what defines how many IP's are in the network block
assigned to you.

I'm clueless as to what all of these mean. Would you guys mind
telling me what I can do with these addresses? Sorry, I am a total
newbie to DSL and networking.

You want usable IP's for anything you intend to do. You may want to
do some reading on IP networking, and network addressing. It's not
light reading but it's the basis for all your misunderstandings here.

Jeff

 

[Chris C.]

Thank you guys so much! Your posts have helped in my understanding greatly