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Ok, I have no trouble setting up my server, or connecting to said server with my personal machine, but when my friend attempts to join we get this message:

Internal client error: java.net.UnknownHostException: session.minecraft.net

A quick google search seems to suggest that this is because his version is different than mine, except he's running MY FILES. (I copied my .minecraft folder and transferred them to his laptop, then we had him login once using his credentials to finalize the transfer)

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marked as duplicate by Ender, KatieK, Frank, Jeffrey Lin, Schism Jul 12 '13 at 23:28

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
did you use the starting command from this answer after that first login? That would be a reason why you need to set online-mode to false, since directly starting the Minecraft client without using the launcher will not validate your login –  Zommuter Jan 16 '12 at 19:33
    
@Tobias: I used that command with the added name command to get him and another friend onto the lan without them both being 'player', yes, but that was only AFTER we got them to login in the first place to discover they were both PLAYER. Im still unsure why exactly we were getting the Internal client error msg. I can only assume I did something wrong with the transfer of files to his labtop, any ideas? (note both of my friends have legit accounts and have used them to login on their systems for that 'first time'. I don't know why were having such trouble lanning. –  Ender Jan 16 '12 at 23:16

4 Answers 4

up vote 10 down vote accepted

The problem is that either the server cannot connect to Minecraft.net or that the person getting that error doesn't have a legitimate Minecraft account and so the server is refusing access.

The way to solve this is either to get all players a premium Minecraft account, or to change online-mode to false to stop it from checking the validity of the other account.

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+1, but what do you mean by "either"? It is mandatory for all players to have a premium Minecraft account, everything else means one pirated it. But changing online-mode to false is still helpful since having to connect to a second server (that of minecraft) may indeed be responsible for connection issues –  Zommuter Jan 16 '12 at 19:28
    
what do you mean by the SERVER cannot connect? I'm attempting to do an offline lanning session, why should I need to connect to do that? –  Ender Jan 16 '12 at 23:18
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@Ender Ther sever checks with minecraft.net whether the account connected it a real account as a safety measure, change to offline mode stops this check and allows pirated copys to connect. –  Ronan Forman Jan 16 '12 at 23:35
    
@Ender - See my comment on your own answer, but this is by design. –  Shinrai Jan 16 '12 at 23:40
    
I don'y understand and still dont understand.. The thing is I dont know how to set up the LAN World AT ALL. I have Minecraft Version 1.3.1 And It lets me open to LAN world so I do but It doesnt work And when I try to join one It doesn't Work AT ALL. Unless my brother Is Doing the old fashioned way he says with programming the server, and I don't get programming at ALL really >.<. Help me with this please I wanna do it with my brothers and sis so I dont only have to be with the same brother EVERY SINGLE TIME.. Please? –  user30704 Aug 11 '12 at 0:46

You see, with online-mode set to true, the server tries to authenticate every player with the official Minecraft servers as they try to join.

You sound as if you're trying to play with no connection outside of your LAN, thus the server is failing because it can't find session.minecraft.net to authenticate the players.

By setting online-mode to false, you're telling to server to quit bothering trying to authenticate you and your friends with the mothership because you know it won't be able to find it, because you have no internet connection.

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AHHHHH. I fully understand now, which would explain also why they suddenly became PLAYER. See, I figured they were already 'authenticated' when they logged in for the first time under their credentials before they just 'played offline'. I thought such authentication was SAVED to each individual machine, thus allowing us the 'play offline' option. I see I was in error. –  Ender Jan 17 '12 at 10:56
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@Ender - Authentication is every time to allow using your account on more than one machine but to prevent people from using the same accounts simultaneously. Looks like we all should have been more explicit about this, sorry. –  Shinrai Jan 17 '12 at 17:37
    
@Ender Then you've probably run into the second player kicking the first out because they have the same name? If so, see here(It says Linux but it includes a command that it says works for Windows also). While it may seem difficult, it is possible to successfully multiplayer Minecraft with no internet. I've done so myself. :) –  John the Green Jan 17 '12 at 18:08
    
yea i figured all that out in the first night after i set the mode to false, if you check my comments on the OP you'll see me discussing it with Tobias briefly. Thanks though! –  Ender Jan 18 '12 at 8:34

Nevermind, I changed the server properties "Online Mode" to FALSE and it worked.

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If I remember correctly, this actually turns off account authentication to the main servers. So, either you're trying to play with the SAME account, or he has some kind of problem accessing minecraft.net. (If it's the former, buy a second account.) –  Shinrai Jan 16 '12 at 16:30
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Of course you can't foresee the future, but since this is basically what Ronan suggested you should accept his answer since it's a bit more elaborative on what the problem was –  Zommuter Jan 16 '12 at 19:31
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@shinrai Ive already been through this, I'm not trying to pirate anything. You people are so quick to assume the worst, I assume this is why I'm getting downvoted AGAIN, but this is the second time I've encountered a minecraft issue and people automatically downvoted and screamed PIRATE. jeez louise. –  Ender Jan 16 '12 at 23:12
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@Shinrai: its not about what I want, its about whats available. Internet at my location is shaky at best. It literally took us 20 hours of doing NOTHING on my connection but attempting to download minecraft to get my one friend the game. (he's on a mac so i couldnt give him my files, I have a pc.) –  Ender Jan 16 '12 at 23:44
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@Ender - Well, so be it then! There's absolutely nothing wrong with offline mode (aside from difficulty differentiating between players!) –  Shinrai Jan 16 '12 at 23:47

Refresh your DNS cache.

  1. Press Windows-R
  2. Type cmd, press Enter.
  3. Type ipconfig/flushdns, press Enter.
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While technically this could be the problem, it's overwhelmingly likely to be something else. –  fredley Oct 10 '12 at 17:02

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