Bitcoin Core developers are debating whether the reference client should continue supporting CJDNS, an optional encrypted IPv6 routing network, after a seeder database check found only seven reliable or "good" nodes active on the network. The discussion began in a GitHub issue focused on whether the low adoption justifies the ongoing maintenance burden and security risks of keeping the privacy transport layer inside Bitcoin Core.
During automated testing of a CJDNS-only node setup, Core developer Marco Falke reported that his instance could not connect to more than three or four distinct peers at any given time. Another contributor then queried a network seeder database containing 25 known CJDNS addresses. While 22 addresses responded to basic handshakes, only seven met the technical criteria for being reliable, well-behaved peers for block and transaction propagation. Developers caution that this seeder query does not represent a complete census of every operating node, since private or unadvertised nodes may exist outside public lists.
CJDNS is an encrypted IPv6 mesh-network overlay that uses public-key cryptography for address allocation and distributed routing. Bitcoin Core added native CJDNS support in version 23.0 in 2022, allowing node operators to route peer traffic over CJDNS alongside IPv4, IPv6, Tor and I2P. Unlike Tor, it is not a full anonymity network, but it encrypts traffic end to end and can make traffic analysis and filtering harder. The current proposal concerns only node networking and peer discovery. It would not change block validation, transaction rules, mining, script rules or consensus logic.
A key security concern is the eclipse attack. If a node runs exclusively over a network with only seven healthy peers, an attacker needs relatively few resources to isolate that node by controlling all of its incoming and outgoing connections. This could allow the attacker to delay block announcements, censor transactions, or attempt double-spend attacks against unconfirmed transactions. Standard IPv4, IPv6, or Tor routing mitigates eclipse attacks by diversifying connections across netgroups and ranges, but an extremely small peer pool undermines that protection.
In addition to security issues, developers point to the maintenance burden of CJDNS integration. Because CJDNS uses specially formatted IPv6 addresses, the Bitcoin Core codebase requires custom handling logic, dedicated launch arguments like -cjdnsreachable, and specialized edge-case workarounds. These custom paths introduce bug risks and complicate refactoring of the networking stack. Several contributors have offered a "Concept ACK" toward deprecating the protocol, signaling agreement with the high-level goal but not a final decision to remove code.
On the other side, contributor Jon Atack argues that low usage may stem from limited awareness and integration rather than a lack of underlying value. Automated CJDNS peer discovery was only integrated into Core in early 2025, and before that operators had to manually configure peer addresses. Atack has volunteered to personally maintain the CJDNS integration code. Proponents say alternative mesh protocols like CJDNS could serve as emergency fallback channels if networks like Tor or I2P face centralized blocking or nation-state filtering. No final decision has been made, and if CJDNS support is removed, Bitcoin Core would simply stop managing CJDNS peer connections internally without affecting the broader Bitcoin network or consensus rules.
