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Raul Gavira
Raul Gavira

What Are Negative UNLs?

The Negative Unique Node List (or Negative UNLs) is a feature of the XRP Ledger’s Consensus Protocol which allows the network to make decisions during partial network failures. According to the XRPL Foundation, the Negative UNL is a list of trusted validators that are either offline or malfunctioning. This list is verified via consensus and communicated to the network by the active UNL validators. 

Although the reasoning for implementing negative UNLs is straightforward (the network has to rely on the active UNL participants to stay operational) it is still an exciting concept to explore as it solves issues other networks face during outages. In short, using negative UNLs allows servers (or nodes) to keep running without needing to reconfigure to another UNL. This also means that new ledger versions can be validated and formed even if several UNL validators are offline.

What Are The Roll of Negative UNLs?

When operating a server on the XRPL, the default connection configuration is set to the recommended UNL. However, each server can still connect to another (maybe preferred) UNL if the operator wishes to do so. The default and primary UNL comprises 35 trusted entities that are anticipated to behave favourably toward the network’s longevity and health. This also means they will likely not collude against you as a server operator. Their job is to validate proposed transactions and update the state of the ledger which then becomes the last-closed ledger. Such a state is only achieved with a quorum (consensus/agreement) of 80%. 

For a multitude of reasons, it is unreasonable to expect validators to be online 24/7. In fact, they can become temporarily affected due to maintenance, internet problems, human error and even targeted attacks/hacks. As such, UNL validators can occasionally end up disconnecting from the network. In the unlikely event that over 20% of validators go offline, the network ceases to validate the new ledger versions. Instead, the remaining servers provide past and tentative transactional data until 80% of the validators are online again. This is advantageous as it ensures no transaction outcomes are changed after the last-closed ledger has been shared. The only downfall of this design is that the network could stop making progress if several of the trusted validators went offline. In the case of the XRPL, a total of 8 or more validators need to go offline before the network stops making progress. 

For more information regarding quorum requirements and negative UNLs click here.

Can You Become A (UNL) Validator?

The simple answer is: Yes, you can become a validator. However, to become a UNL validator you must be voted in by the other trusted entities of the UNL. Before this, you must first run a rippled server as a validator on the XRPL network and prove that you are a trusted participant of the XRPL network. This includes connecting to a network of peers using Peer Protocol, relaying cryptographically signed transactions, and maintaining a local copy of the complete shared global ledger on a continuous basis.

Hereunder, you will find an overview of the process:

Understanding The Traits of A Good Validator

  1. Availability → always running and submitting votes
  2. Agreement in votes
  3. Timely votes issued
  4. Clear identified owner
  1. Install a rippled server
  2. Enable validation on your rippled server → providing a validator token in your server’s ʼrippled.cfg file
  3. Connect to the network → three different configurations you can use to connect validators to the XRPL network: discovered peers, proxies and public hubs. 
  4. Verify your network connection → several methods to verify that validator has a healthy connection with the XRPL network
  5. Provide domain verification → helps validation list publishers and other participants understand who runs the validator

For more information on how to become an XRPL validator click here.

Conclusion

The UNL is an essential part of the XRPL network since most servers are connected to it by default. This means that a lot of nodes are dependent on this list of entities that validate transactions via the Consensus Protocol and update the shared state of the ledger accordingly. Finding a way to mitigate validator node failure is therefore crucial for the health and longevity of the ledger. 

In come the negative UNL. These inactive validators have accidentally been disconnected from the network (e.g. due to an Internet outage) and must subsequently be ignored by the active validators during the consensus process. If several validators go offline simultaneously, active validators use the negative UNL to adjust their online UNLs to the minimum 80% required. With a quorum requirement of 80%, 60% of the total validators must reach consensus. However, if for whatever reason more than 20% of validators go offline at once, the remaining servers will have to wait till they reach 80% of validators to make a decision.

Raul Gavira
Raul Gavira

He is a 29-year-old content writer and digital marketer with a passion for Crypto, NFTs and anything else of the digital realm. Born and raised internationally, he speaks three languages fluently: Spanish, English & Dutch. His first interaction with crypto was around 2013, but he was not a firm believer of it at first. Half a decade later he found himself entering the crypto-sphere and since then he has been mesmerized by it. His goal is to continue to learn more about this fascinating world and contribute positively to its growth.