[Popular Science] What exactly are BT seeds and magnet links?
BitTorrent
The BT seed we usually refer to actually refers to a file containing resource information generated by the BitTorrent protocol. Different from traditional network transmission protocols, BitTorrent protocol is a resource sharing protocol based on Peer-To-Peer (P2P), that is, user-to-user mode. It adopts a decentralized idea and does not require a special file publisher or publishing platform.
Protocols such as HTTP and FTP that we usually use require a central publisher to publish files on the network, that is, a point-to-many form. Of course, if the central publisher is banned or deletes resources for some reason, then we will not be able to download our beloved ~~Miss Sister~~ resources.
Therefore, in theory, as long as a torrent is released, the resources contained in the torrent will always exist on the Internet.
The idea of the BitTorrent protocol is to divide a file into n blocks of equal size , and the block size must be an integer power of $2^k$. For example, a 100M file is divided into 100 small blocks according to the size of each block of 1024k, and each block contains index information and Hash value , and our download process is actually a block exchange process.
The resource publisher of the BitTorrent protocol will make a file containing resource download information, such as Tracker server address , file size , file name , block file size, etc. .torrent , according to the requirements. This process is what we usually call seeding .
The picture below is a seed I made using BitComet software, you can take a look.
Seeding
If we want to download BT resources, we must first obtain the corresponding .torrent files, and then download them with special download software, such as BitComet, qBittorrent, utorrent, etc. The download process is roughly as follows:
- Read
.torrentfile information and load it into memory - Get the address in the file
Trackerand connect to the Tracker server - The Tracker server responds to download requests, records your IP and informs other downloaders of their IP addresses
- You connect with other online downloaders, exchanging chunks that each doesn't have
- Verify the block information obtained, if it is different, you need to download it again
It can be seen from this that Tracker is a very important thing. Once the Tracker server is blocked, we will not be able to download it. Thus, magnet links were born.
magnet link
A magnet link (Magnet URI scheme) is a computer program for information retrieval and document download in a peer-to-peer network. Unlike the uniform resource locator based on the "location" connection, the magnet link is based on the content of the metadata (metadata) file, which belongs to the uniform resource name
For example this string of links:
magnet:?xt=urn:btih:53SWOUDWKG6ORSKTJHHE3QXTIBOGU5WU
magnet It is the protocol name; xt it indicates the resource location point; urn:btih it indicates the Hash method name, and the most important thing is the only string of 40-digit hexadecimal numbers behind it. Magnetic links use DHT technology (Distributed Hash Table, Distributed Hash Table) and PEX (Peer Exchange) to realize the "random" dissemination of resources, which cannot be prohibited at all.
The essence of magnet link downloading is to turn everyone into a Tracker server, associate resources with downloaders, and save part of the information for each downloader. That way, when downloading a resource, you only need to look for a downloader who has the desired resource.
For example, A knows B, B knows C, and C knows D and E; if A wants to know E, he can get to know D through the introduction of B and C, and there is no need for A to find E one by one.
The specific principle is more complicated, you can watch the paperclip video to learn more
how to download?
Having said so much, how to download BT seeds or magnet links?
Use a dedicated client
Common clients on the Internet that support BT downloads include BitComet , uTorrent , qBitTorrent , Motrix , FDM, etc. Of course, the most important thing is the Tracker server. You can get a better Tracker address through a project on GitHub .
third party support
Baidu Netdisk, 115 Netdisk, Thunder and other software can also be downloaded. But due to copyright and some other issues, ~~everyone understands~~, the effect is not very ideal.
living comfortably without anybody's help
If possible, you can use Aria2 to build it yourself
The above content is only for simple science popularization, and the wording in some places may be inaccurate or wrong, please bear with me~ Please
explain to me the wrong place, and I will try to modify it~
reference link
Principles of BitTorrent Protocol and MagNet Protocol
Paperclip: Stop asking me what is a BitTorrent
What is the principle of BT seed?