Maximize DHT swarm size by adding other DHT bootstrap servers

[kilves76]

These DHT bootstrap servers could be added to maximize the size of the DHT swarm available to a Tribler client:

dht.libtorrent.org:6881
dht.transmissionbt.com:6881
router.utorrent.com:6881
router.bittorrent.com:6881
dht.aelitis.com:6881
router.bitcomet.com:6881

The initial swarms are regimented according to the app as many torrent apps do not permit adding more, or users don't know how. Adding them all as default maximizes a Tribler peer's chances of finding content and is a benefit to everyone.

[synctext]

thnx!
Do we override Libtorrent DHT bootstrap defaults?

[ichorid]

AFAIK, we don't. At least there are no mentions of it in the code.

[ichorid]

By default, Libtorrent uses dht.libtorrent.org bootstrap node.

[qstokkink]

This does seem like something we could easily implement though: the add_dht_node and add_dht_router calls exist in libtorrent and should be available in the bindings (on session instances).

[egbertbouman]

We're already adding DHT routers manually. We just need to extend the list in the DownloadManager:

tribler/src/tribler-core/tribler_core/modules/libtorrent/download_manager.py

Lines 35 to 39 in 4999bfc

	DEFAULT_DHT_ROUTERS = [
	("dht.libtorrent.org", 25401),
	("router.bittorrent.com", 6881),
	("router.utorrent.com", 6881)
	]

[ichorid]

@egbertbouman , what's the difference between add_dht_router and setting dht_bootstrap_nodes then? The former adds to the latter, right?

[egbertbouman]

@ichorid Right, the add_dht_router function adds to the list and the dht_bootstrap_nodes sets the list.

[arvidn]

dht routers are not treated as regular nodes. They are only used when bootstrapping the DHT fails. for example if there aren't any nodes saved from the last session, or they all fail to be contacted.

routers could also be made to never be saved in the routing table, but I don't think there's any logic like that currently, but doing so might make sense in the future.

[ichorid]

@synctext , so, is it possible to increase connectivity and get to bigger swarms by adding more bootstrap nodes to libtorrent?

[arvidn]

it's not obvious to me that it would have that effect. Especially if the routing table is already "full". And if the routing table isn't full, it may be caused by some connectivity problem where nodes are lost too frequently to be replenished. In which case the tweaks to the table maintenance settings might be in order. Say, more frequent bucket refreshes.