DNS

A "domain name system" (DNS for short) provides a resolution of a domain (for example geti2p.net) into an IP address (for example 81.7.7.63). In I2P, an eepsites IP(+port) is its "destination" (a very long string), so resolution goes by eephost->destination (for example [see ref]).

A real life use of DNS would be a phone book: to call someone, you lookup the their name in the phone book. A phone book's equivalent would be a DNS server in clearnet, or a name registry in I2P.

How to get to the destinations for the corresponding services?

An I2P router has a local DNS system in itself called "addressbook", storing the domain names and destinations, allowing for resolution without contacting a name registry. In a regulat environment, this would be "/etc/hosts" (or "C:\Windows\System32\drivers\etc\hosts" for Windows).

How to populate the router's addressbook?

There are several name registries in I2P, which keep a list of domain name-destination pairs. If you are subscribed to one or more, the router will regularly check in the background whether its registries offer new domain names or updated ones of the old ones, then fetch the new/updated entries and apply them to the addressbook.

Subscription in this context is a router having a list of name registries to fetch a domain/destination list from. You can add or remove a subscription from your router easily.

This system can be described as decentralized for these arguments:

1. If one name registry goes down, you can still subscribe to another one (and you should do that anyway).
2. No name registries are needed for any resolving to take place, given that a list of domain/destination pairs has already been fetched.
3. Name registries often exchange their lists by other ones, to keep theirs more synchronized, making it possible to get (roughly) the same list from different name registries.
4. A service operator might choose to register their eepsite with different registries at once.

There are many registries and everyone can open their own. Here is a selection of registries:

Registries

Site	Operator	Reliable
stats.i2p	By zzz, one of the main developers of I2P.	Yes
reg.i2p	Developers of i2pd	Yes
inr.i2p	Unknown	Probably yes
identiguy.i2p	Unknown	Probably yes
isitup.i2p	Unknown	Probably yes
i2pjump.i2p	Unknown	Probably yes

It is also possible to simply provide a list of domain names and destinations without being acting as a registry accepting new domains. A selection of such services:

Providers of lists with domain names and destinations without registration function

Site	Operator	Info	Reliable
http://i2p-projekt.i2p/hosts.txt	Operated by the I2P project.	This list contains long existing eepsites and serves to provide a "basic list".	Yes
http://notbob.i2p/hosts.txt	Notbob		Yes

What are jump URLs/Services?

If a router doesn't know the destination of an eepsite, and the name registries subscribed to doesn't have this domain (or they have and the router haven't fetched it yet), a "jump URL" can be used instead. A jump URL is in the format of: http://[[domain]].i2p/?i2paddresshelper=[[the long destination string]]

This lets a router to register this domain within themselves, allowing for the local resolutions of [[domain]] to be for [[the long destination string]].

A jump URL is easy to construct, for example, take the destination that was given at the top of this page for i2p-projekt.i2p, and prefix it to make it look like this: http://i2p-projekt.i2p/?i2paddresshelper=8ZAW~KzGF[...]

A jump service provides these jump URLs from their list. Mostly, these services are hosted within an existing registry, since a registry already has a lot of domains (by nature), increasing the chances of a jump URL being given successfully.

A selection of jump services (put a hostname like "i2p-projekt.i2p" at the end of one):

Jump services

URL	Info
http://stats.i2p/cgi-bin/jump.cgi?a=	This site is operated by ZZZ, one of the main developers of I2P.
http://i2pjump.i2p/jump/	This page collects the address books from different pages and provides them.
http://notbob.i2p/cgi-bin/jump.cgi?q=	This site is operated by NotBob.
http://inr.i2p/jump/	It is not known who operates this page. She seems to be trustworthy.
http://reg.i2p/jump/	This site is operated by the developers of I2PD.

What are these different addressbooks?

This section applies to Java I2P routers, as I2Pd doesn't have multiple addressbooks.

If you are going to add a domain name in your addressbook by yourself via SusiDNS, you would see that there are several addressbooks.

The router addressbook is the one that the router operates. You will notice that this is a very long list of domains. This is because the lists fetched from the subscribed-to registries are stored here, and these registries (by nature) have a lot of domains. You don't need to touch this to add your eepsite, you would instead register it with a registry.

The private addressbook, is, private. This means it is shared with no one else and only in your router. It can be used, for example, to save a service that you operate (like a SSH or an FTP server) or a private forum that no one else should see. Normally, you do not need this, unless you do.

The local address book can be used to seeprate the services that you operate from the ones in the router addressbook. For example, if you operate an eepsite (for example a private blog), you can enter them here. Normally, you also don't need this addressbook. This addressbook's entries will shadow the ones in the router addressbook's ones.

The public addressbook should only be used by experts and experienced eepsite operators. It can be used to publish a list of domain names and destinations yourself.

Which registries should I use?

Anyone being able to run a registry is a double-edged sword. The good edge is that there are always enough registries, talking to and syncing with each other, letting you to use anyone of them with almost no downtime. The bad edge is that a malicious person might host a registry, giving you wrong destinations, causing you to go to fraudulent eepsites, and potentially putting you in a bad situation (passwords being stolen, deanonymization attacks, etc). This is why there are only a few registry subscriptions in an out-of-the-box router, and why one should explore a registry before adding it to their subscription list.

Glossary

Glossary

Term	Meaning
IP address	In order for computers to be able to communicate (talk) with one another, they need an IP address, like names for humans. In principle, every computer that is connected to the Internet has an IP address.
Eepsite	A website in the I2P network
I2P Router	A piece of software that lets you browse the I2P network, and most likely letting you to read this.
I2P service	A service that is offered in the I2P network. These can be eepsites, chat servers, games, anything you can imagine.
Destination	An equivalent of an IP address in the I2P network. The difference being that it is very long, and can be imagined as a pack of an IP address and a port.
Clearnet	The regular internet.
local	On your own computer, not shared with anybody else.

External sites

• http://i2p-projekt.i2p/en/docs/naming
• http://i2p-projekt.i2p/en/faq