WOW nice score! Yeah since it says LAN it is either a BBA or the LAN adapter. We need more pictures of the stickers on the inside of the adapter. The LAN adapter was released only in Japan and was only good for browsing the internet, not gaming. The model numbers of these are HIT-0300.
From Sega Scream site...
Alternate Titles ドリームキャスト・LANアダプタ
Release Dates ?
Release Prices ? (JP)
Product IDs HIT-0300 (JP)
Barcodes ? (JP)
In Packages Dreamcast LAN Adaptr, manual, Dream Passport 2 for LAN disc
"This Dreamcast LAN Adapter is a bit of an odd accessory to collect. You can’t use it to play online games at all, only surfing the web! It was designed only to work with the “Dream Passport 2 for LAN” software included.
It used a Fujitsu MB86967 chip and supported only 10 Mbit speed instead of 100 Mbit as the standard Broadband Adapter (BBA) does.
You cannot use the official Dream Passport 2 for LAN GDROM disc on any region other than Japan and you cannot use the Dreamcast LAN adapter as intended without it.
Hackers have found an additional use in dumping Dreamcast games with the LAN adapter."https://segascream.com/dreamcast-lan-adapter/