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.
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