BGP Basics for IPv4 Buyers: What You Need to Know Before Acquiring Addresses
BGP and ASN basics matter when you buy IPv4: once you acquire addresses and complete an RIR transfer, you typically need to announce your block so traffic can reach it. BGP (Border Gateway Protocol) is how IPv4 prefixes are advertised to the internet; ASN (Autonomous System Number) identifies your network. This post covers BGP and ASN basics for IPv4 buyers and what you need to know before acquiring addresses.
What BGP Is and Why It Matters for IPv4 Buyers
BGP is the routing protocol that advertises IPv4 (and IPv6) prefixes to the internet. When one network wants to tell others how to reach its IPv4 space, it announces its prefixes via BGP. Other networks learn those routes and send traffic accordingly. So when you buy and complete an RIR transfer, you own the block—but the internet does not know how to reach it until you (or someone acting for you) announce it via BGP.
BGP basics for IPv4 buyers: ownership (from the RIR transfer) is one step; making the block reachable is another. If you run your own network and plan to announce your block, you need BGP and typically an ASN. If you use your IPv4 with a hosting provider or cloud (e.g. they announce your block for you), you may not run BGP yourself. So buy and then decide how you will announce and use the space. Our buying guide walks through the acquisition; BGP and ASN are part of putting the block to use.
What an ASN Is and When You Need One
An ASN (Autonomous System Number) identifies your network to other networks. When you announce IPv4 via BGP, you do so under your ASN. RIRs (ARIN, RIPE, APNIC, LACNIC, AFRINIC) allocate ASNs. You typically need an ASN when you buy and plan to announce your block yourself (e.g. you have your own network and peer with other networks).
If you buy and use the block with a hosting provider or cloud, they may announce it under their ASN. In that case you may not need your own ASN. So ASN need depends on how you use the IPv4 you acquire. Our buying guide covers the acquisition; ASN is a separate RIR request if you need one.
What IPv4 Buyers Need to Know Before Acquiring Addresses
Define your needs. Prefix size (/24, /23, /22, etc.), region (which RIR), and timeline. That shapes what you look for and what process you follow.
Understand how you will use the block. Will you announce it yourself (need BGP and likely ASN), or will a provider announce it for you? BGP and ASN basics matter when you run your own network; they matter less when a provider handles announcement.
Get the block. Our buying IPv4 guide walks through finding a block, due diligence, LOA, agreement, and completing the RIR transfer. Complete the transfer; then you own the block.
Announce and use. Once you own the block, announce it via BGP (yourself or through a provider). If you announce yourself, you typically need an ASN from your RIR. BGP basics: your IPv4 prefix is advertised so other networks can route traffic to you.
How to Act
- Define your needs. Size, region, timeline, and how you will use the IPv4 (announce yourself vs use with a provider).
- Buy IPv4. Follow our buying guide: find a block, do due diligence, sign LOA and agreement, complete the RIR transfer.
- Decide on BGP and ASN. If you will announce the block yourself, request an ASN from your RIR if you do not have one, then configure BGP to announce your IPv4 prefix. If a provider will announce for you, coordinate with them.
- Verify. Once announced, verify that your IPv4 block is reachable (e.g. check routing tables, test connectivity).
BGP and ASN basics are what IPv4 buyers need to put their block to use after they buy. Understanding BGP and ASN before acquiring addresses helps you plan; our buying guide gets you from acquisition to ownership so you can then announce and use your space.