How can I see or detect how many peers have seen a transaction?

[Kazimir]

Some clients such as MultiBit or Mycelium show how many peers have seen a certain transaction. To give an indication of its propagation throughout the network.

How do they do this?

[jimmyscratchlab]

https://en.bitcoin.it/wiki/Network

[Kazimir]

Do you mean my Bitcoin node can only tell how many peers have sent a 'getdata' request in response to my node's 'inv' message?

Is there a way I can see or estimate how many nodes have seen someone else's transaction? This would require me knowing about it, of course, but suppose I do. I have just seen someone do a tx and I wanna see how fast it propagates. What are my options?

[grau]

Connect to a large number of random nodes and send them getdata for the tx.

[Kazimir]

Connect to a large number of random nodes and send them getdata for the tx.

Thanks, makes sense. What's a good way to connect to a large number of nodes? Is there some way I can get a list of nodes, preferably distributed all over the world?

[Mike Hearn]

bitcoinj just watches for inv messages.

[malevolent]

What's a good way to connect to a large number of nodes? Is there some way I can get a list of nodes, preferably distributed all over the world?

Add addnode=<ip> entries in bitcoin.conf, or use the addnode=<ip> argument in command-line, if you want to connect to more than 125 nodes (https://github.com/bitcoin/bitcoin/blob/master/src/net.cpp#L64), then I think you will need to change -maxconnections=<x> to something higher.
Blockchain.info is very well connected so you could add some of the nodes they are connected to: https://blockchain.info/ip-log

[Kazimir]

Does bitcoind / Bitcoin-Qt by default relay *all* txs it receives? I mean not just the tx I send from my wallet, but also forwarding any txs it receives from any of its connected nodes to all other nodes?

Blockchain.info is very well connected so you could add some of the nodes they are connected to: https://blockchain.info/ip-log

Not at the moment (but good tip, thanks )

[malevolent]

Blockchain.info is very well connected so you could add some of the nodes they are connected to: https://blockchain.info/ip-log

Not at the moment (but good tip, thanks )

http://webcache.googleusercontent.com/search?q=cache%3Ahttps%3A%2F%2Fblockchain.info%2Fip-log&oq=cache%3Ahttps%3A%2F%2Fblockchain.info%2Fip-log&aqs=chrome..69i57j69i58.1512j0j4&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8

other pages also seem to be cached, though I only checked the first three.