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Understanding IP Ranges

Posted on 2011-09-14
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Last Modified: 2012-05-12
Our company IP addressing is as follows:

10.213.0.0/19 or 255.255.224.0 (1st Network)
10.213.253.0/29 or 255.255.255.248 (Router network to Sister Company)
10.213.253.8/29 or 255.255.255.248 (Router to ISP)

On our MPLS Router (Inside IP 10.213.253.2/29) I have been asked to supply an IP address for loopback on the range 10.213.0.x/32 or any /32 host IP.

What range of IP would match this?
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Question by:DHPBilcare
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Garry-G earned 250 total points
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Just pick any IP that is not part of an otherwise used IP subnet. Effectively, it's just an additional IP for your router, usable for things like PPP originator, VPN, Tunnels, etc ...
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by:Ken Boone
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Well we really need to understand the whole ip scheme of things.

So you have a 10.213.0.0 /19 network which can mean a few things.

It might mean that you company supplied you with this block of IPs for you to use internally however you see fit.

So right now that block is 10.213.0.0 - 10.213.31.255

So that is the equivalent of 8190 hosts on the network.  Which is either crazy to put on one network or sheer laziness or lack of understanding.

So most likely what was intended is for your part of the company that has that block to further subdivide or subnet that block into usable ranges that you can disperse however you want.

In other words you might use 10.213.0.0 / 24 and 10.213.1.0 / 24 and 10.213.2.0 / 24 for different vlans in your internal network, but the rest of your company just sees the 10.213.0.0/19.

So if that is how it is being used you need to find out how your ip block has been allocated and then determine what you have left to use.

So lets look at the 3rd octet.  It can range from 0 - 31 and still be in your assigned block.  Lets say you have used 0 - 10 already as /24 networks.  So we can't reuse them.  So maybe we reserve the .31 portion of the address specific to loopbacks.  So we won't use those as a /24 instead we will use them as /32 addresses.

It really depends on how your IP scheme is actually laid out.  For instance on your 1st network - do the PCs on that network really have a subnet mask of /19?

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by:DHPBilcare
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At the moment the network is flat but the potential to grow and add VLANS in the future as required.  

We have been allocated the range listed for our own use.
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by:Ken Boone
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so if its a flat /19 network then you will not be able to give the router anything in the 10.230.[0-31].x range as it will overlap.

You will have to go outside of that block in order to do that.

Is the deal such that each company under the conglomerate got a separate block of addresses to use?  If so you will have to see what is free.  Since you guys are flat with a /19 nothing is available for you to use out of that block.  The router will not let you configure an overlapping ip address on the same router.
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by:Garry-G
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Can you say what the Loopback IP will be used for?
Anyway, I would suspect you could maybe use a /32 from the 10.213.253.0/24 network, e.g. 10.213.253.255/32 ...
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by:DHPBilcare
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Sorry my mistake.

The MPLS router is outside of our firewall on a subnet of 10.213.253.0/29.

As this router requires the IP for loop back could I not simply exclude .31 portion from the internal pool and use one address on said router?  e.g. 10.213.31.1 /32.
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by:Ken Boone
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No because your router has an inside interface on the 10.213.0.0 / 19 interface.  If you created another interface on the router using 10.213.31.1 the router will bark at you and tell you that you are trying to use an overlapping interface.  You have to go outside the 0-31 range.

You can re-subnet your network so you don't have this problem in the future.  You said you want to grow, but you can't grow in this address space unless you re-address your network and use it more efficiently.
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by:Ken Boone
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This really has nothing to do with the pool of addresses it has all to do with the fact that it overlaps.
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