<p>I would add two points to those already mentioned: First, if you cannot accept inbound connections (because you are behind NAT or have specifically disabled them) you won't really be helping the network. Second, if you are running any version earlier than 0.3.24, you could actually be harming the network, due to a bug in those versions.</p>

<p>For some reason that isn't well-understood, the Bitcoin peer-to-peer network is consistently short of available inbound connection slots. This makes it more difficult for newly-started clients to establish a resilient connection to the Bitcoin network. If you can accept inbound connections, leaving your client running helps reduce this problem.</p>

CC BY-SA 3.0
2014-05-23T14:48:44.400Z
@DavidSchwartz, When you mentioned *"the Bitcoin peer-to-peer network is consistently short of available inbound connection slots"*, do you mean that this is not a problem other networks like torrents have?
Pacerier
CC BY-SA 3.0
2011-10-17T21:43:26.633Z
@DavidSchwartz.  Why is it a questionable decision.  The risk of UPnP comes from the router not the clinet.  i.e. user installs malicious software on computer and uses UPnP to modify firewall to allow attacker inbound access and then notifies attacker of vulnerable system.  However Bitcoin client creates no risk. If uPnP is turned off the feature does nothing (client can't force a uPnp connection when disabled in router).  If UPnp is enabled the system is already at risk (how much is subject to debate).  Personally I think the risk is overstated for most systems.
DeathAndTaxes
CC BY-SA 3.0
2011-10-17T22:18:00.287Z
It's questionable because a program shouldn't assume the right to open a port in a UPnP setup. That's something a program should request permission to do. Also, there were political issues involving that decision and competing suggestions that I don't think were resolved in a good way.
David Schwartz
CC BY-SA 3.0
2011-08-31T20:24:48.600Z
Thanks.  It would help if you could also indicate the impacts of running short of available inbound slots.
nealmcb
CC BY-SA 3.0
2011-09-01T11:17:01.077Z
If you have compiled bitcoin with UPNP support (the pre-packaged version has this) and your router supports it, you can accept inbound connections even behind NAT
laanwj
CC BY-SA 3.0
2011-09-01T11:20:01.010Z
UPnP was enabled by default in the pre-compiled Windows client because the problem of the lack of inbound connection capacity was so severe. Many people, including myself, consider this a questionable decision.
David Schwartz
CC BY-SA 3.0
2011-08-31T18:02:58.570Z
2011-08-31T20:36:27.007Z
2011-08-31T20:36:27.007Z
David Schwartz
<p>Turning your client off gives it a chance to fall behind the network. The client is so bad at downloading the block chain from other clients, that if you fall more than few days behind, you'll have to download a copy of the block chain from the nightly archive in order to catch up.</p>

CC BY-SA 3.0
2012-06-24T03:34:17.400Z
2012-06-24T03:34:17.400Z
user1513
<p>Bitcoin is a peer-to-peer network, which means that the clients not only receive the blocks from other clients, but send out the blocks to other clients. (You may notice the "connections" number in the bottom right of the original client. You can think of this as "peers" in a torrent client). So yes, by having your client open you are technically helping relay the recent blocks out across the network faster than they would get their otherwise, but there is really no reason to keep a client running all the time.</p>

<p>At one point, the client also doubled as a CPU miner, but we are far past the point where that is useful from a security point of view.</p>

CC BY-SA 3.0
2014-05-23T14:43:22.623Z
@lemonginger, What do you mean by *"but we are far past the point where that is useful from a security point of view"*?
Pacerier
CC BY-SA 3.0
2011-09-02T04:01:32.433Z
I accept as correct, but [David Schwartz's answer](http://bitcoin.stackexchange.com/questions/300/should-i-leave-the-bitcoin-client-open/302#302) is worth checking for some additional details and limitations.
nmat
CC BY-SA 3.0
2011-08-31T17:37:19.367Z
2011-09-02T19:01:02.827Z
2011-09-02T19:01:02.827Z
lemonginger
<p>Some people recommended that I leave my Bitcoin client open because it <em>helps</em> the network.</p>

<p>Apart from the security implications, why should I do this? I thought that miners were the ones responsible for validating transactions and including them in the blockchain. What role does the Bitcoin client play in the network?</p>

<bitcoin-core><client><network>
Should I leave the Bitcoin client open?
nmat
# Should I leave the Bitcoin client open?

(Asked by: username_0 on 2011-08-31)

Some people recommended that I leave my Bitcoin client open because it *helps* the network.

Apart from the security implications, why should I do this? I thought that miners were the ones responsible for validating transactions and including them in the blockchain. What role does the Bitcoin client play in the network?

**Tags:** bitcoin-core, client, network


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## 3 answers

### Answer by username_7 on 2011-08-31. Score: 34 | Accepted answer

Bitcoin is a peer-to-peer network, which means that the clients not only receive the blocks from other clients, but send out the blocks to other clients. (You may notice the "connections" number in the bottom right of the original client. You can think of this as "peers" in a torrent client). So yes, by having your client open you are technically helping relay the recent blocks out across the network faster than they would get their otherwise, but there is really no reason to keep a client running all the time.

At one point, the client also doubled as a CPU miner, but we are far past the point where that is useful from a security point of view.

> **Comments:**
> **username_0**: I accept as correct, but [username_1 username_1's answer](http://bitcoin.stackexchange.com/questions/300/should-i-leave-the-bitcoin-client-open/302#302) is worth checking for some additional details and limitations.  
> **username_2**: @username_7, What do you mean by *"but we are far past the point where that is useful from a security point of view"*?  

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### Answer by username_1 on 2011-08-31. Score: 46

I would add two points to those already mentioned: First, if you cannot accept inbound connections (because you are behind NAT or have specifically disabled them) you won't really be helping the network. Second, if you are running any version earlier than 0.3.24, you could actually be harming the network, due to a bug in those versions.

For some reason that isn't well-understood, the Bitcoin peer-to-peer network is consistently short of available inbound connection slots. This makes it more difficult for newly-started clients to establish a resilient connection to the Bitcoin network. If you can accept inbound connections, leaving your client running helps reduce this problem.

> **Comments:**
> **username_4**: Thanks.  It would help if you could also indicate the impacts of running short of available inbound slots.  
> **username_5**: If you have compiled bitcoin with UPNP support (the pre-packaged version has this) and your router supports it, you can accept inbound connections even behind NAT  
> **username_1**: UPnP was enabled by default in the pre-compiled Windows client because the problem of the lack of inbound connection capacity was so severe. Many people, including myself, consider this a questionable decision.  
> **username_3**: @username_1.  Why is it a questionable decision.  The risk of UPnP comes from the router not the clinet.  i.e. user installs malicious software on computer and uses UPnP to modify firewall to allow attacker inbound access and then notifies attacker of vulnerable system.  However Bitcoin client creates no risk. If uPnP is turned off the feature does nothing (client can't force a uPnp connection when disabled in router).  If UPnp is enabled the system is already at risk (how much is subject to debate).  Personally I think the risk is overstated for most systems.  
> **username_1**: It's questionable because a program shouldn't assume the right to open a port in a UPnP setup. That's something a program should request permission to do. Also, there were political issues involving that decision and competing suggestions that I don't think were resolved in a good way.  
> **username_2**: @username_1, When you mentioned *"the Bitcoin peer-to-peer network is consistently short of available inbound connection slots"*, do you mean that this is not a problem other networks like torrents have?  

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### Answer by username_6 on 2012-06-24. Score: -1

Turning your client off gives it a chance to fall behind the network. The client is so bad at downloading the block chain from other clients, that if you fall more than few days behind, you'll have to download a copy of the block chain from the nightly archive in order to catch up.


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