Hi

A rather complex topic in I2P is the addressbook. I try to give some light on it. Some basic guidelines first.

The addressbook is a app and local database on your I2P router system, which resolves "Petnames" like echelon.i2p into the b64 address, which is used internally by I2P router. As this translation happens local only, the Petnames needs to be known to the addressbook and stored locally.
A predefined set of these entries are distributed with I2P router installation package. Others may be entered manually or via subscription hosts.
Subscription hosts do offer their list of addressbook entries for download and to be integrated into the local addressbook database.
If a user trying to reach a eepsite which is not known in local addressbook, I2P shows a helper link to ask these subscription hosts for this unknow eepsite. If the b64 entry is found, the user is asked to enter this entry into local addressbook, too.
Due to "trust only yourself" the I2P team does not revoke and remove I2P addresses from users addressbook database or files. Which results in:
once entered, it is taken forever! If the eepsite/hidden service is gone, the addressbook entry will stay and cannot be used for other services.

Advanced break: each user may have a different b64 entry for echelon.i2p in their addressbook, no central instance does control this! which results in: a once used xyz.i2p entry maybe reused for a new b64 entry, BUT on older I2P routers it may conflict with a already existant entry and the user must decide what to do with this conflict (use old or new one), the addressbook app will ask the user.

The addressbook app does offer a publication service itself. It also includes a private entries file, which is never published or sent to other hosts. Entries in the private addressbook are only used by the local I2P router.
Entries in the master addressbook are merged with the entried taken from the subscriptions into the router addressbook. If the user enables the feature in addressbook app to publish the entries, the app copies this router addressbook as a file into the local eepsite folder as hosts.txt.

If the user enables the eepsite and hands out his eepsite address, other users can reach the hosts.txt file on the eepsite and integrate the new entries into their master addressbook. The addressbook app does not sync those automatic! Only manual entered subscription hosts are fetched automaticly.

So a local I2P router just needs to enable its eepsite and hand out his address (e.g. gbgf.i2p) and others can fetch the hosts.txt via gbgf.i2p/hosts.txt and may enter this link as a new subscription service.

echelon