Wissen
Readdressing: when IP addresses have to change, and how a lease avoids it
Readdressing, also called renumbering, moves a network from one set of IP addresses to another. The change on your own servers is the small part: the work is in everything outside your network that knows the old addresses. You avoid it by holding addresses that stay with you, your own or a lease that says in writing you keep the block for as long as you renew.
When readdressing happens
- You change provider. Addresses your hosting or cloud provider assigns stay with it when you leave. A block of your own, or one leased to you, can go with you: how each provider takes one is in the BYOIP guides.
- A lease ends, or the lessor takes the block back. Depending on the contract, a lessor may reclaim a block at the end of a term, reissue it to another customer, or move you to different addresses to tidy its own space, sometimes during the term.
- The block changes hands. A holder can sell a block that is leased out, and a lessor's own right to a block can end. What happens to your lease then depends on what the contract says.
- The registry steps in. A regional internet registry can deregister resources when their fees go unpaid or the holder no longer has the contract the registry requires: in the RIPE NCC region, independent resources need one with a sponsoring LIR or with the RIPE NCC itself.
- Your network changes. A merger, a new upstream, a data center move or a redesign can leave addresses that no longer fit.
- Your IPv6 prefix came from your provider. Provider-assigned IPv6 space changes with the provider. RFC 4192 describes how to renumber an IPv6 network without a flag day.
What changes when the addresses change
Every place below holds your old addresses, and most of them are outside your own network. The IETF's RFC 5887, "Renumbering Still Needs Work", lists the same pain points from the network side.
| Where the old addresses live | What to do |
|---|---|
| Your DNS: A and AAAA records, SPF and other TXT records | Lower the TTLs days ahead, then change the records |
| Reverse DNS | Set PTR records on the new block before mail or services move |
| Partners' and customers' allowlists and firewall rules | Ask early: their change windows set your timetable |
| VPN peers, IPsec and tunnel endpoints | Update both ends, and keep the old endpoint up until the far side has moved |
| Certificates and licenses bound to an IP | Reissue them for the new addresses |
| Mail reputation | Warm up sending on the new addresses, and check their history first |
| Location databases | Publish a geofeed for the new block before traffic moves |
| Routing: ROAs, route objects, letters of authorization | Create them for the new block and withdraw the old ones when traffic stops (RPKI, route objects, LOAs) |
| Your own records: IPAM, monitoring, documentation | Update them as each service moves |
How to plan a readdressing
- Find every place the addresses appear. Start from your IP address management and DNS zones, then firewall and VPN configurations, then the partners who allow you by IP.
- Get the new block ready first. Registry records, ROA, route object, reverse DNS and geofeed in place, and the block checked against the blocklists before anything moves to it.
- Lower DNS TTLs a few days before the move.
- Run old and new side by side. Move services one at a time, and tell partners with fixed allowlists the new addresses before you need them.
- Warm up mail on the new addresses rather than moving all sending at once.
- Keep the old block until its traffic stops, then withdraw its announcements, ROAs and records.
What a lease should say
A lease decides whether you will ever have to do this for your lessor's reasons rather than your own. Before you sign, look for:
- No reclaiming or reissuing during the term. The block is yours to use until the term ends, and nobody else's.
- No forced move to other addresses, during the term or on renewal.
- Renewal on the same block, and on what conditions.
- Notice and a replacement if the lessor is ever required to withdraw the block, for example by a registry, an authority or an upstream: how many days, and whether you get an equivalent block at the same price.
- What happens if the lessor sells the block or its own right to it ends.
The rest of what to check is in the IPv4 lease contract.
Where RTM Networks fits
Every lease from us comes with our Block Continuity Guarantee, at no extra charge and not as a paid tier: we do not reclaim, reissue or renumber a block we lease to you, during the term or on renewal, and when you renew you keep the same block. It holds for as long as you renew on time and are not in a termination process under our Terms. We would withdraw a block only if a registry, a competent authority or an upstream that announces the space required it, or if our own right to the block ended. You would then get at least 60 days' written notice and an equivalent block of the same size, in the same registry where available, at the same price for the rest of the term. If we could not offer one, or you would rather not take it, you could end that service on the withdrawal date without further liability. It is in our Terms of Service.
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