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Bitcoin / Development & Technical Discussion / Re: Loads of fake peers advertised on bitcoin network

on: July 27, 2021, 07:38:35 AM

Quote from: piotr_n on July 14, 2021, 02:37:39 PM the thousand 'new buckets' approach and each node being able to access only 64 of them, does not seem to be helping much, considering that all the nodes advertise incoming addresses without checking them. It helps against a personal attack - without it one could connect to a victim node and immediately fill all of its "new" buckets with junk. It only slows down a network-wide junk spread. Quote from: piotr_n on July 14, 2021, 02:37:39 PM Now imagine scenario that you're starting a new node, with a brand new IP. It is going to have a hard time getting incoming connections anytime soon, considering that it competes with hundreds of thousands of fake IPs. Competes in which way? If a node has a set of 20 addresses, 19 of which are junk and just 1 real and it wants to connect to somebody, then after some failed attempts it is going to connect to the 1 real one. There is no hurry. Trying to connect to a non-listening node (junk) takes a few seconds. Quote from: piotr_n on July 14, 2021, 02:37:39 PM Plus every node looses time trying to connect to these fake addresses. Not sure what is the core's algo of choosing a new IP to connect to, but whatever it is, it will surely also have to deal with a lot of dead tries. Yes, the failed attempts will waste some time. Opening new connections in Bitcoin Core happens in CConnman::ThreadOpenConnections(): https://github.com/bitcoin/bitcoin/blob/1488f55fa57a1400a57be837b574183f019c7855/src/net.cpp#L1832 the address to connect to is chosen by calling CAddrMan::Select(): https://github.com/bitcoin/bitcoin/blob/1488f55fa57a1400a57be837b574183f019c7855/src/net.cpp#L2047 with some further filtering afterwards. CAddrMan::Select() is defined here: https://github.com/bitcoin/bitcoin/blob/1488f55fa57a1400a57be837b574183f019c7855/src/addrman.cpp#L413 it can chose from the "new" and "tried" tables.

2

Bitcoin / Development & Technical Discussion / Re: Loads of fake peers advertised on bitcoin network

on: July 14, 2021, 11:07:54 AM

Quote from: piotr_n on July 13, 2021, 03:13:17 PM What is the core's algorithm for selecting addresses to return after receiving getaddr request? It starts from here: https://github.com/bitcoin/bitcoin/blob/531c2b7c04898f5a2097f44e8c12bfb2f53aaf9b/src/net_processing.cpp#L3681 Quote from: piotr_n on July 13, 2021, 03:13:17 PM Does it only pick those from the "tried" buckets? No. But it deliberately avoids addresses it has tried to connect without success and some other "terrible" ones: https://github.com/bitcoin/bitcoin/blob/531c2b7c04898f5a2097f44e8c12bfb2f53aaf9b/src/addrman.cpp#L46 called from here: https://github.com/bitcoin/bitcoin/blob/531c2b7c04898f5a2097f44e8c12bfb2f53aaf9b/src/addrman.cpp#L571 `vRandom` contains all addresses, both "new" and "tried". Quote from: piotr_n on July 13, 2021, 03:13:17 PM Same for sending spontaneous addr messages: does it have to "try" it first, before it can route a new addr to its peeers? I am not completely sure, but it seems like I'm getting (most of) those fake addresses from a legit bitcoin core peers. I have a suspicion that because of the algorithm bitcoin core uses for routing new addresses, it's somehow facilitating this problem. Here is what happens when an `addr` message is received: https://github.com/bitcoin/bitcoin/blob/531c2b7c04898f5a2097f44e8c12bfb2f53aaf9b/src/net_processing.cpp#L2753 under some conditions, every address from the `addr` message is relayed to ~2 other, random peers: https://github.com/bitcoin/bitcoin/blob/531c2b7c04898f5a2097f44e8c12bfb2f53aaf9b/src/net_processing.cpp#L2801 No attempt is made to verify that a bitcoin client is listening on that address by connecting to it. That would be too slow and create another problem - DoS by sending the victim's address to e.g. 10k bitcoin nodes, all of them rushing immediately to verify if somebody is listening there. Also, it could be that the address is of a legit node, which is just shut down temporarily. Quote from: ETFbitcoin on July 13, 2021, 11:16:05 AM You shouldn't assume everyone use Bitcoin Core. OP is developer of alternative full node client, so it's likely he's talking about his gocoin node. I assumed it is Bitcoin Core because the post reads like "I have 700k addresses ... does Bitcoin Core have limit...". Thanks for the clarification!

3

Bitcoin / Development & Technical Discussion / Re: Loads of fake peers advertised on bitcoin network

on: July 13, 2021, 10:53:51 AM

Quote from: piotr_n on July 12, 2021, 10:32:28 AM All my nodes' peers databases are now over 700k records ... Does bitcoin core have a limit of peers upon witch it won't accept new addresses into the database? Yes, the limit is (1024+256)*64 = 81920 addresses (see https://github.com/bitcoin/bitcoin/blob/7e1ba37b5daceda222b138cbf61bbdeda87d21fd/src/addrman.h#L159-L162). How come you have 700k+ records? How can you tell whether an address is "completely random" or an address of a legit node that is down?

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