Five ways managers and network engineers at independent ISPs can work together to better use IPv4 addresses before they run out. These slides accompany our guide "How to Conserve IPv4 Addresses While You Plan for IPv6" available at www.ZCorum.com/ipv6.

1. How to Conserve
IPv4 Addresses
While You Plan
for IPv6
5 Ways non-technical
managers and network
engineers can work
together to better use
IPv4 addresses before
they run out Conserve sCarCe IPv4 resourCes
We know, it sounds like a bunch of tree-hugging non-
sense. But, the truth is that IPv4 addresses—the ones
we’re currently using to connect to the Internet—are
pretty much an endangered species.
Lucky for us, IPv6 can provide an unimaginably large
number of addresses. Not ready for IPv6 yet, you say?
Then you’d better make like a treehugger and start using
the IPv4 address space you already have more wisely. That
will at least buy you some time to run IPv6 testing and
develop an IPv6 implementation plan.
This handy how-to guide offers five ways to get the
most out of your existing IPv4 allocation. Share this
information with your network engineers and use it
to discuss the things they may already be doing to
maximize your current IP space, and to begin evaluating
your next steps for implementing IPv6.
For more information on IPv6 and the things you
should be doing to prepare your network, please visit
http://www.zcorum.com/ipv6.
Copyright ©2010 ZCorum. All rights reserved. Page 1

2. 1
KeeP DetAIleD ReCoRDs Demand
You know how when it snows the bread and This is one area in which engineers could really use
milk shelves at the grocery store are empty? some help from their non-technical managers.
That’s poor demand planning and poor inventory
Be sure you communicate with your network staff
management.
so they understand how many new customers you
Same goes for your network. You should be monitoring typically acquire in a given period, as well as how many
inventory, utilization and demand and keeping meticu- leave your service. If there are sales promotions coming
lous records. up that may boost the normal number of customers
acquired, be sure to give your technical team a heads-
up. Knowing the net number of customer additions will
Inventory
help them keep adequate addresses in inventory.
Just like the grocery store, you need to know how many
addresses you have in stock.
You can keep your records up-to-date by reviewing your
IP inventory monthly. That’s sufficient for most indepen- Inventory
you have
Know how many addresses
dent broadband providers; but, if you are adding many
Utilization
new customers each month or are approaching 85% assigned to
Know which addresses are
whether or
equipment and users, and
utilization of your IP allocation, you may need to review
used
more frequently. not they are really being
Demand
tomers you
Know how many new cus
Utilization typically acquire in a given time period,
jects that may
as well as any network pro
Now that you know how many addresses you have, you ignments, and
require new address ass
need to know how many are actually in use. plan accordingly
Just because your inventory list says an IP address is
in-use doesn’t make it so. An IP logged “in-use” may
have been given up when that equipment was removed
from service, moved or upgraded, but your inventory
records might not have been updated.
One way to determine utilization is to use ping tests or
network scanning tools. Just remember that these tools
generally can’t ping anything behind a router or firewall,
so you may have to check those items manually.
Copyright ©2010 ZCorum. All rights reserved. Page 2

3. 2
ConsolIDAte subnets Why do I lose addresses on each subnet?
Without getting too technical, a subnet Every time you create a subnet, you lose three ad-
is a logically visible subdivision of an IP dresses. Technically, you didn’t “lose” them, you just
network. For ISPs, the main benefit of subnetting is that can’t allocate them anywhere else because they have a
it partitions your address space into a tree-like routing specific function to perform in the subnet.
structure.
The first address in the subnet serves and the network
The downside to creating a whole bunch of subnets address. The last address in the subnet serves as the
is that each one steals three addresses for its own use. broadcast address, so neither of these is a valid host for
That’s three addresses that you can’t allocate to paying end users. Another address in the subnet is also needed
customers. to serve as the gateway or logical interface address.
Why should I consolidate subnets?
As IPv4 addresses become scarce—and as it gets harder
to qualify for allocations from ARIN, which is already
happening—you need to conserve your existing space
and use it wisely.
If you can roll several small subnets into a larger one,
then you can recover three usable addresses for each
subnet you eliminate. If you’ve got 8 subnets in one
head end or central office and you can consolidate
that into just 3 subnets, you can recover 15 addresses.
Now apply that same theory to the rest of your head
ends and central offices and we’re talking significant
addresses recovered.
That could give you enough IPv4 inventory to keep add-
ing customers for a few more months while you finalize
your IPv6 plans. You’re starting to see the benefits of
being an IPv4-conservation tree-hugger now, right?
Copyright ©2010 ZCorum. All rights reserved. Page 3

4. 3 4
ReClAIm ADDResses fRom lImIt stAtIC IP ADDResses
ReseRveD Pools
You’ve probably received requests from your
Services that use PPP authentication, like customers for static IP addresses. In the spirit
dial-up and some DSL networks, require reserved pools of good customer service, you’ve probably said “okay”.
of IP addresses. Check the utilization and shrink these
Stop that!
pools accordingly.
Why shouldn’t I give out static addresses?
Drain the Dial-up Pool
If you’re handing out static IP addresses, that address is
Back in the day, you probably had an ocean (or at least
no longer part of the pool you can share among other
an Olympic-size pool) full of reserved addresses to
customers.
support your dial-up services. That was okay because
there were actually people swimming in it and making Residential customers don’t usually need a static
use of those addresses. address. Unless they’re running a web server out of
their home, that is.
Fast forward to when you deployed broadband and the
majority of those folks ditched dial-up. Did you drain But that would be a violation of your residential terms
some of the water out of the “reserved for dial-up” IP of service, wouldn’t it?
pool, or were you so focused on your new broadband
service that you forgot?
When should I give out a static address?
Now’s the time to go take a look. If you’ve still got that
Reserve a pool of static IP addresses for your business
Olympic-sized pool but only a handful of people are us-
customers.
ing it, it’s time to down-grade to a kiddie pool. Reclaim
as many addresses from that reserved pool as you can They may be running their own web servers or need a
and move them into inventory for your broadband dedicated IP for remote access or secure transactions.
network. In these cases, it is appropriate to assign a static IP
address.
Check Utilization on Other Pools
Perhaps you can move more addresses out as dial-up
customers upgrade to broadband. You can reclaim
whatever is left when (or if ) you stop offering dial-up.
If you’ve got other pools that aren’t being fully utilized,
reclaim those addresses whenever possible.
Remember to add your dial-up pool or any others
you’ve created for dedicated purposes to the regular
inventory check we suggested in the first section so you
can keep an eye on them.
Copyright ©2010 ZCorum. All rights reserved. Page 4

5. 5
Get IP AlloCAtIons fRom Calculating your true utilization from
A sInGle PRovIDeR multiple providers
If you get an allocation from your backbone Now, let’s say you reach 85% utilization of the pool
provider and from your managed service provider from your managed service provider and ask for an
or ARIN, you’ve got multiple inventories to manage. additional allocation.
That’s eating up your time in tracking all those separate
ARIN will look at all your available IP space to see if
allocations.
you’re really at 85% utilization.
Plus, having many sources for IP space may put you at
You’ve got 256 addresses in your /24 from AT&T and
risk of getting your next IPv4 allocation request denied.
1280 addresses in your five “portable” /24s. Your total
Why? available allocation is 1,536 addresses.
Because ARIN requires that you be utilizing at least On average, you’re using about 1,088 addresses. That
85% of your current allocation before you can justify puts your utilization at about 70%, not 85%.
requesting a new one.
So, you can’t get more any more space from your
And by current allocation, they mean all addresses to managed service provider or ARIN until you relinquish
which you have access. the AT&T space you’re not using.
Calculating your true allocation from
multiple providers
Let’s say you have an AT&T backbone. AT&T probably
gave you a /24 (256 addresses) as part of your service
package, even if you didn’t ask for it and don’t use it. How to apply for IP space from arIn
If this is your first allocation request to ARIN, follow
You also have a managed service provider that gives these steps:
you five /24s (1280 addresses), which you use so 1. Review ARIN allocation policies in the
Number Resource Policy Manual to confirm
you can change backbone providers—for optimal that you qualify for a direct allocation.
bandwidth pricing, of course—and not have to re-IP
2. Get an Autonomous System Number (ASN),
your whole network. You can just pick up this so-called create an ARIN web account, POC handle
“portable IP space” and take it with you to the next and ORG ID.
backbone provider. You use that allocation for all your 3. Complete and submit the forms for your
initial IPv4 or IPv6 allocations.
network equipment and end users.
4. ARIN will evaluate your request and approve
ARIN will add your AT&T allocation and your “portable” it, or contact you for further information to
determine eligibility.
allocation to get your total current allocation.
5. Once the request is approved, pay the
applicable fees and sign the Registration
Services Agreement. Upon receipt, ARIN
will notify you that your addresses are
available for use.
Copyright ©2010 ZCorum. All rights reserved. Page 5

6. Get IPv4 allocations directly from ARIN summary
For small organizations, you’ll have to go through a You’re a card-carrying, IPv4-conserving tree-hugger
third party, such as your backbone or managed services now, aren’t you?
provider, to request IPv4 allocations.
But there’s no need to chain yourself to a rack of servers
But, if your network is large enough, you might be bet- to make a statement about your new-found passion for
ter off getting your IPV4 allocations directly from ARIN. IPv4 conservation.
You can check the requirements for ISPs on ARIN.net.
Simply check in with your network engineers and share
this handy how-to guide. Check off the techniques
Get IPv6 allocations directly from ARIN they’re already using:
When you implement IPv6, ARIN prefers that ISPs • Keep Detailed Records
submit direct allocation requests. Check ARIN.net to • Consolidate Subnets
learn how you can qualify for direct IPv6 allocations. • Reclaim Addresses from Reserved Pools
• Limit Static IP Addresses
• Get IP Allocations from a Single Provider
Then, find out what help or resources they need from
you to implement additional techniques to use your
existing IP space more efficiently.
Once those engineers realize that you have a clue about
IPv6 (if you don’t, read this IPv6 primer) and what it
means for your network, they’ll be better able to help
you figure out how to prepare for IPv6. And that’s
good for everybody—you, your engineers, and your
customers.
Copyright ©2010 ZCorum. All rights reserved. Page 6