Team Cymru Bogons Blacklist
The Team Cymru Bogons blacklist (or blocklist) identifies invalid IP addresses from unallocated or reserved ranges that should not appear on the internet.
Updated on 17 Jun 2026: We updated this guide to clarify fullbogons, update cadence, RFC6598, and safer Team Cymru Bogons filtering.
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Check if you are listed on Team Cymru Bogons Blacklist
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TechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftWhat is the Team Cymru Bogons blacklist?
The Team Cymru Bogons blacklist is a DNS-based blocklist (DNSBL) that contains bogon IP addresses. A bogon is an address that should not appear as a source or destination on the public internet because it is reserved, special-use, unallocated, or otherwise not globally routable. This includes RFC1918 private ranges such as 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, plus other special ranges that need careful treatment in edge filters. The purpose of this blacklist is to improve network security by filtering invalid traffic that appears in spoofing, scans, and DDoS traffic.
This blocklist is used by network administrators to block traffic at the network perimeter. It is not intended to be used as a filter for email servers, as it does not track IPs based on sending reputation. Technically, when an IP address is checked against the bogons.cymru.com zone, the list responds with an A record of 127.0.0.2 if the IP is a bogon. A TXT record can also be queried to identify the specific bogon prefix the address belongs to.
- Blocking traffic from unroutable IP addresses helps prevent spoofed traffic, scans, and malformed routing leaks.
- Filtering invalid packets reduces unnecessary load on border routers and firewalls.
- Keeping bogon filters current reduces the risk of accepting traffic from prefixes that should not be visible on the public internet.
Bogons, fullbogons, and update cadence
Traditional bogons are martians and prefixes not allocated by IANA to a Regional Internet Registry. Fullbogons go further: they include prefixes that have been allocated to an RIR but not yet assigned by that RIR to an ISP, hosting provider, enterprise, or other end user. That distinction matters because fullbogon filters change more often and need tighter operational controls.
Team Cymru provides bogon data through DNS, HTTP lists, routing registries, and BGP peering. The HTTP fullbogon lists for IPv4 and IPv6 are updated every four hours, while traditional bogon lists are updated when IANA allocations and special prefix reservations change. BGP peering is the better fit for automated router-side filtering, but teams still need to test changes before enforcing drops.
- Treat 100.64.0.0/10 as a special case. It is shared address space under RFC6598, not ordinary RFC1918 private space, so filtering it without checking local carrier-grade NAT use breaks legitimate internal traffic.
- Keep local exceptions for prefixes you intentionally use internally.
- Review border router, firewall, and route-map behavior before null routing bogon or fullbogon prefixes.
Who runs the Team Cymru Bogons blacklist?
This bogon blacklist is maintained by Team Cymru, an internet security and threat intelligence organization. The data is based on relevant RFCs, IANA IPv4 allocation data, and Regional Internet Registry information. Team Cymru offers the bogon reference data as a community service for network operators who need perimeter filtering data.
How do I get removed from the Team Cymru Bogons blacklist?
A listing on the Team Cymru Bogons blacklist is different from a normal email blacklist or blocklist. You do not request delisting from this list. If the IP being checked is listed, the IP is either reserved, special-use, unallocated, not assigned for public routing, or being evaluated through the wrong source address.
The usual problem is service misconfiguration. For example, an email or security gateway might be checking a private source address instead of the public sending IP. The fix is to correct the local configuration, not to submit a delisting request.
- Verify the exact IP address being queried and compare it with the public IP shown by the sending service.
- Check whether the flagged address is an internal range such as 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, or a special-use range such as 100.64.0.0/10.
- Ask the network or email administrator to remove Team Cymru Bogons from email sender reputation checks.
- Use the list only where bogon filtering fits, such as border routers, firewall policy, route maps, or other perimeter controls.
What is the impact of being listed on the Team Cymru Bogons blacklist?
The impact of this blocklist on external email deliverability is very low to none. Since it lists non-routable addresses or addresses that have not been assigned for public use, it does not affect legitimate email sent from a correctly configured server with a valid public IP address. If a mail server incorrectly uses this blacklist for sender reputation checks, it blocks the wrong thing and creates local delivery failures. The issue is incorrect local setup, not poor sender reputation.
