What does a node do?

[naidray]

Many useful information on running a bitcoin core wallet.
I heard some 3rd party provides incentive for running a node for bitcoin network. Not sure whether still providing or not.

[BlueStackz]

So, does it mean, there are only 6000 people are running bitcoin core and doing mining.
If we assume, 50% are bitcoin core wallets means, only 3000 individual miners?

[achow101]

So, does it mean, there are only 6000 people are running bitcoin core and doing mining.

No. This means that there are ~6000 people running a full node software. It could be Bitcoin Core, Bitcoin XT, btcd, etc. There are many out there but mostly Bitcoin Core is used. You can see the actual distribution of node software used on https://bitnodes.21.co/nodes/

If we assume, 50% are bitcoin core wallets means, only 3000 individual miners?

No. Most miners mine at a mining pool, so they do not need to run any type of node software. The pool runs the software. Some of them run Bitcoin Core others run their own custom implementation so they can customize it as they see fit. Even so, running Bitcoin Core (or any full node) does not mean that you are mining. However you can mine using Bitcoin Core or by pointing a miner at Bitcoin Core which will give all of the necessary data required to mine blocks.

[Blue_Panda73]

If it is such a simple configuration, why are there so fewer nodes in the network? I remember there are only 6000 full nodes.

6001 now

I guess people don't want to pay the overhead in running a full node, when they don't get any reward. I only start the core for a while when I want to check for coins reeceived, and to keep the blockchain up to date.

There's currently 5667 reachable nodes*, it has decreased drastically. Unless you're a developers or want extra security, a SPV node would often suffice. The main problem of Bitcoin Core is disk space and bandwidth, that's pretty much all why Bitcoin users do not want to run it. Why run Core when you can run SPV clients right?

*Only nodes that enabled port 8333 and allowed connection from bitnodes.

Is it possible to DDos those 5667 nodes and take down bitcoin network? 5667 nodes is no a large number.

[achow101]

If it is such a simple configuration, why are there so fewer nodes in the network? I remember there are only 6000 full nodes.

6001 now

I guess people don't want to pay the overhead in running a full node, when they don't get any reward. I only start the core for a while when I want to check for coins reeceived, and to keep the blockchain up to date.

There's currently 5667 reachable nodes*, it has decreased drastically. Unless you're a developers or want extra security, a SPV node would often suffice. The main problem of Bitcoin Core is disk space and bandwidth, that's pretty much all why Bitcoin users do not want to run it. Why run Core when you can run SPV clients right?

*Only nodes that enabled port 8333 and allowed connection from bitnodes.

Is it possible to DDos those 5667 nodes and take down bitcoin network? 5667 nodes is no a large number.

Maybe. Bitcoin Core only allows a maximum of 125 connections to it. It has DoS protection built in so any node that is sending bad messages to it will get blocked and the connection will be dropped, so it may be hard to do.

[Blue_Panda73]

If it is such a simple configuration, why are there so fewer nodes in the network? I remember there are only 6000 full nodes.

6001 now

I guess people don't want to pay the overhead in running a full node, when they don't get any reward. I only start the core for a while when I want to check for coins reeceived, and to keep the blockchain up to date.

There's currently 5667 reachable nodes*, it has decreased drastically. Unless you're a developers or want extra security, a SPV node would often suffice. The main problem of Bitcoin Core is disk space and bandwidth, that's pretty much all why Bitcoin users do not want to run it. Why run Core when you can run SPV clients right?

*Only nodes that enabled port 8333 and allowed connection from bitnodes.

Is it possible to DDos those 5667 nodes and take down bitcoin network? 5667 nodes is no a large number.

Maybe. Bitcoin Core only allows a maximum of 125 connections to it. It has DoS protection built in so any node that is sending bad messages to it will get blocked and the connection will be dropped, so it may be hard to do.

But if the node receives a lot of request, how does it know which connection to drop, or which one is from attacker?

[shorena]

-snip-
But if the node receives a lot of request, how does it know which connection to drop, or which one is from attacker?

Its a TCP connection, you know the sender. If the sender fills you with nonsense you end the connection and refuse to accept it again for some time.