Due Diligence

IPv4 Due Diligence Checklist

Before purchasing IPv4 addresses, thorough due diligence is essential. This checklist by IPv4Center.com covers every verification step — from blacklist scans to ownership confirmation and BGP history review.

Why Due Diligence Matters

Protecting your investment by verifying every aspect of an IPv4 block before purchase.

IPv4 address blocks are a significant investment. Unlike traditional assets, IP addresses carry technical, legal, and reputational risks that can only be uncovered through systematic due diligence.

A block that looks clean on the surface may have hidden issues: blacklist entries that degrade email deliverability, hijacking history that complicates BGP announcements, or ownership disputes that can freeze the transfer.

This checklist provides a structured, step-by-step framework for evaluating IPv4 blocks. Use it alongside our IP Due Diligence tool for automated checks.

Complete Due Diligence Checklist

Work through each category systematically. Every item should be verified before completing a purchase.

1. Ownership & Registration

Verify the legal ownership and registration status of the block.

WHOIS record verification

Confirm the seller is the registered holder of the block via WHOIS lookup. Cross-reference with the relevant RIR database.

RIR registration confirmation

Verify the block is registered with RIPE, ARIN, APNIC, LACNIC, or AFRINIC and that the registration is active and current.

Ownership chain review

Trace the block's ownership history. Look for gaps, disputed transfers, or blocks held by dissolved entities.

Abuse contact verification

Confirm that abuse contact information is current and valid. Outdated contacts may indicate abandoned or neglected blocks.

Legacy vs allocated status

Determine if the block is legacy (pre-RIR) or allocated. Legacy blocks may require additional agreements (e.g., ARIN LRSA/RSA).

2. Blacklist & Reputation

Check the block against all major blacklists and reputation databases.

Multi-database blacklist scan

Run the block against 300+ blacklist databases using the IP blacklist check tool. Check every IP in the range, not just the network address.

Spamhaus SBL/CBL check

Spamhaus is the most impactful blacklist. SBL listings indicate known spam sources; CBL indicates compromised hosts. Both significantly affect email deliverability.

Email deliverability assessment

If you plan to use the IPs for email (SMTP), check the block against email-specific blacklists using the email blacklist check.

Sender reputation score

Check major email providers' reputation systems (Google Postmaster, Microsoft SNDS) for any existing reputation data on the IPs.

Historical abuse reports

Review if the block has been the subject of abuse complaints. Check AbuseIPDB, Project Honeypot, and similar databases.

3. BGP & Routing

Analyze the routing history and current announcement status.

BGP announcement history

Review the block's routing history using the BGP lookup tool. Look for consistent, legitimate announcements from authorized ASNs.

Hijacking detection

Check for unauthorized route announcements. BGP hijacking events are a critical red flag and may indicate ongoing security issues.

RPKI/ROA status

Verify if RPKI ROAs exist for the block and whether they match the expected origin ASN.

Current visibility

Check if the block is currently visible in the global BGP routing table. Unannounced blocks are generally preferred (clean slate).

Upstream provider compatibility

Confirm the block can be announced from your ASN and that your upstream providers will accept the route.

4. Legal & Compliance

Address legal aspects and transfer compliance requirements.

Transfer policy compliance

Verify the transfer complies with the relevant RIR's transfer policy. See our guides for RIPE, ARIN, APNIC, and LACNIC transfers.

No pending disputes

Confirm there are no active disputes, litigation, or claims against the block with any RIR or legal entity.

Escrow payment arrangement

Use an escrow service to hold payment until the RIR confirms the transfer. Never pay the full amount before RIR confirmation.

Transfer agreement review

Review the transfer contract carefully. Ensure it includes warranties about block cleanliness, ownership, and post-transfer support.

Sanctions and export controls

Verify neither party is subject to trade sanctions or export restrictions that could impede the transfer.

5. Technical Validation

Verify technical aspects of the block before finalizing.

Subnet boundaries

Confirm the block aligns with proper CIDR boundaries. Use the subnet calculator to verify.

No sub-allocations

Verify the block has no outstanding sub-allocations, delegations, or split assignments that could complicate the transfer.

Reverse DNS configuration

Check the current rDNS setup. Plan for DNS delegation changes post-transfer.

Geolocation accuracy

Verify the block's current geolocation mapping. Consider geofeed configuration post-transfer if location accuracy is important.

Due Diligence Tools

IPv4Center.com provides a comprehensive suite of free tools to assist with due diligence verification.

IP Due Diligence Tool

All-in-one automated due diligence check. Scans blacklists, verifies WHOIS, checks BGP routing, and generates a comprehensive report.

IP Blacklist Check

Scan any IP against 300+ blacklist databases. Identifies listings on Spamhaus, Barracuda, and dozens of other providers.

WHOIS Lookup

Query registration details for any IP block. Verify ownership, registration dates, and contact information.

BGP Lookup

Check BGP routing information including origin ASN, announcement history, and upstream providers.

ASN Lookup

Look up Autonomous System information, including announced prefixes and peering data.

Subnet Calculator

Calculate CIDR notation, network ranges, and subnet boundaries. Verify block alignment.

Common Issues Found During Due Diligence

These are the most frequent problems discovered during IPv4 due diligence and how to handle them.

Minor Blacklist Entries

Low

A few IPs listed on minor or regional blacklists. This is common and usually not a deal-breaker.

Action: Request the seller to delist before transfer, or negotiate a price reduction. Minor listings can usually be resolved within days.

Spamhaus SBL/CBL Listings

Medium

One or more IPs on Spamhaus. This significantly affects email deliverability and indicates past abuse.

Action: Negotiate significant price reduction. Delisting requires demonstrating legitimate use and can take weeks. If the entire block is listed, consider walking away.

BGP Hijacking History

High

Evidence of unauthorized route announcements from unknown ASNs.

Action: Investigate thoroughly. If the hijacking was a one-time event years ago, it may be acceptable with a price discount. Active or recent hijacking is a deal-breaker.

Ownership Disputes

Critical

Conflicting claims on block ownership, pending litigation, or blocks held by dissolved entities.

Action: Do not proceed. Ownership disputes can take years to resolve and may result in the block being reclaimed by the RIR.

Sub-Allocations Present

Medium

The block has existing sub-allocations or route objects that need to be cleaned up.

Action: Request the seller to consolidate and clean all sub-allocations before transfer. This should be a precondition in the transfer agreement.

Outdated WHOIS Records

Low

WHOIS contact information is outdated but ownership is clear.

Action: Require WHOIS updates as part of the transfer process. This is normal and easily resolved during the RIR transfer.

Frequently Asked Questions

Common questions about IPv4 due diligence.

How long does a complete due diligence take?

A thorough due diligence can be completed in 1–3 days using our IP due diligence tool for automated checks, combined with manual verification of ownership and legal aspects.

Should I check every IP in the block?

Yes, ideally. For smaller blocks (/24, /23), check every IP. For larger blocks, sample IPs across the range and pay special attention to the first and last IPs, as well as any previously announced subnets.

What if the block has some blacklist entries?

Minor blacklist entries on a few IPs are common and shouldn't be a deal-breaker. Negotiate a price reduction or require the seller to resolve listings pre-transfer. Widespread Spamhaus listings, however, are a serious concern.

Is it safe to buy unannounced blocks?

Unannounced (never routed) blocks can actually be preferable — they represent a clean slate with no routing baggage. However, still verify ownership, blacklist status, and ensure the block isn't on any bogon lists.

Does IPv4Center perform due diligence?

Yes. IPv4Center.com performs comprehensive due diligence on every block listed in our marketplace. Buyers receive a full due diligence report before purchase. We also offer standalone due diligence checks for blocks acquired elsewhere.

What should I do if due diligence reveals issues?

It depends on the severity. Minor issues (outdated WHOIS, a few minor blacklist entries) can be resolved. Medium issues (Spamhaus listings, sub-allocations) warrant price negotiation. Critical issues (ownership disputes, active hijacking) mean you should walk away.

Need Help with Due Diligence?

IPv4Center.com performs comprehensive due diligence on every transaction. Buy with confidence knowing every block is thoroughly verified.

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