As the number of network connected devices grows in a campus environment, pressure to use our organisation’s limited global IPv4 address space as efficiently as possible increases. While IPv6 may provide the longer-term solution, in this presentation we explore the challenges faced by sites in maximising the utilisation of their existing IPv4 address space, and handling address space exhaustion.

1. IPv4 Address Planning
‘Share and Explore’
Chair:Tim Chown, Jisc
tim.chown@jisc.ac.uk

2. Introduction
» Many Janet-connected organisations have long-standing IPv4 address
space, commonly a /16 dating back 20+ years
» Others, especially more recently connected sites, may only have a relatively
small block of address space, perhaps /24 or less
» Open question: how do you manage your address space as it becomes
exhausted, or when your original allocation was relatively small in the
first place?
› And doing that given an ever-growing number of networked devices,
including those connecting wirelessly via eduroam
» Aim of this session is to discuss issues and share ideas
23/03/2016 IPv4 Address Planning ‘Share and Explore’

3. Topics
» Some topics have arisen from my own recent conversations with sites – we
can discuss these and then any other thoughts or questions you may have
» Topics:
› Ongoing address planning – handling fragmentation over time of your of
address space, and reclaiming larger blocks of space
› When to use NAT, and when not
› Tools (IPAM software) used to manage your address space, and mapping
to DNS and DHCP services, etc
› Allocating static IPv4 addresses to user devices
› Planning for IPv6 (dual-stack)
» We can look at each of these in turn…
23/03/2016 IPv4 Address Planning ‘Share and Explore’

4. Ongoing address planning
» An address plan is an evolving, ‘living’ thing
› Likely to be constantly under review
» New demands on your address space, e.g. new buildings, new services,
expanding services (like eduroam)
› May mean you want large contiguous blocks of address space
» Sites with ‘historic’ address space (/16) likely to have become fragmented
over time
› For efficiency, want to ‘shrink-wrap’ allocations to number of hosts in
a subnet
» As you reach exhaustion, this task becomes more difficult
» Is this a problem you recognise? If so, how big an issue is it?
23/03/2016 IPv4 Address Planning ‘Share and Explore’

5. When to use NAT
» An obvious way to conserve use of your global IPv4 address space is to use
Network AddressTranslation (NAT)
» But when / where is it appropriate / acceptable to do so?
› Your eduroam network may be one target – probably the fastest growing
part of your network, with many BYOD devices per person
» In many cases, ‘needs must’
» Always need a certain amount of global address space for public-facing
services
» Some devices may only communicate internally within your site –
no need to have a global address
» Thoughts?
23/03/2016 IPv4 Address Planning ‘Share and Explore’

6. Address management tools (IPAMs)
» Most (all?) sites will be using some form of IP address management (IPAM)
software
› May be a commercial off-the-shelf tool
› Might be home-grown software that has been lovingly crafted and
updated over many years
– Maybe the original author is still with you, or maybe not
› Will typically integrate with DNS and DHCP services
» What are you using?
» Does it do the job you need?
» If not, what are the gaps / problems?
23/03/2016 IPv4 Address Planning ‘Share and Explore’

7. Static IP address allocations
» In many sites, it seems common that users can request static IP addresses
for their devices or services
› Might be servers
› Might also be clients – perhaps less necessary?
» Typically implemented through IP-MAC address mappings
› But note what Stephen Farrell said yesterday about operating systems
and randomising MAC addresses over time
› Good for user privacy, but adds challenges to network management
» Are static IP address allocations something you support?
» Can you continue to do so when facing address exhaustion?
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8. Planning for IPv6 (dual-stack)
» IPv6 is the long-term solution for address space shortages / problems in
Janet-connected sites
» Some deployments happening(as reportedearliertoday – see the slides online)
› Pretty much universally dual-stack (IPv4 alongside IPv6)
› IPv6-only networking will follow, but not quite ready yet, especially for
BYOD environments
» Question: how might you integrate an IPv6 address plan in your IPv4
network?
› Add a /64 IPv4 prefix for each IPv4 subnet, as it is today?
› Or try to start afresh? (with much renumbering…)
› No right or wrong answer, but an interesting challenge
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9. jisc.ac.uk
Other issues?
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Are there any other issues you’d like to
discuss?
Tim Chown
Senior network services developer
Tim.Chown@jisc.ac.uk