A few problems that can arise when attempting to connect a game. Note that these suggestions are made to minimize issues, I do not mean to imply you have to meet every condition here for it to work. Also I am assuming a LAN game, since non-LAN games introduce a whole host of other issues to resolve.
Lack of connectivity ensure everyone is connected to the home LAN (WiFi or cable), free WiFi or someone else's open WiFi can cause problems. If the server and players are not all connected to the same connection in the same way, cable vs WiFi, that can also be a problem.
Logins everyone needs to be logged into their own Minecraft account
Versions make sure everyone is running the same version, this includes the server software if you are using it
Mods if you are using mods, try it without them to make sure they aren't causing problems, easiest way is to move the folder where your mods are stored somewhere else, including the main jar file
Firewalls make sure that your firewall has an exception for the right version of Java, sometimes you can have a few versions installed, which can cause problems. Don't just allow the Minecraft.exe either, since it is just an updater. If your computer is connected to a network that you have told Windows is "public", there are rules in your Windows Firewall that Java set up that will disallow connections from public networks. Try disabling those rules.
Router rules can sometimes disallow connecting to other computers on the same network by default, as a security feature. There's no one way to fix this that works for every router, so you'll have to research your particular router and how to check/change its configuration.
IP addresses try to have a single IP address for each machine, this means don't connect to the wired and wireless at the same time, it can cause problems
Valid IP addresses If you are running Windows, you can get your IP address by running ipconfig, and if you're running OS X or Linux you can use ifconfig (f instead of p). Do this on both machines, and look for an address that starts with one of the following:
192.168. (this is the most common)10. (this is not rare but not common)172. (this is rare!)
These are the beginnings of IPv4 addresses, so a complete address would look like, for instance 192.168.0.25, or 10.10.0.217. (If you're using IPv6 instead of IPv4, then you presumably already know what you're doing, and you don't need a guide like this to help you.)
Make sure that first three digits of the IP address match between the two computers. (This is a slight simplification but is what you want in 99% of cases. Google subnet masks if you want a more complete explanation).
To run ipconfig, you must open the command prompt (cmd) and type in ipconfig, then press enter. You can use the "Run..." command from the Start menu.
To run ifconfig in OS X, you can open Terminal.app from the Spotlight search. (Magnifying glass in the upper right, or command-space.)
If you're on Linux I'll assume you already know how to find your terminal emulator. (It varies too much from one distro to another to give a single set of directions. And if you don't know how to find it, then you're on the wrong OS for you.)
Try Direct Connect various problems can prevent automatic finding from working, try typing the address printed when the world was enabled into the Direct Connect link.
Try Re-installing Minecraft in cases where LAN abruptly stops working, reinstalling can help. Make sure to delete your .minecraft folder and clean with a tool like ccleaner. Be sure to clean registries as well, and backup just to be safe.
Hopefully this covers all of the most common issues.
I was able to talk about my problem to the Creator of the linked Video above myself via Teamspeak.
Here are some things to keep in mind when building a huge farm like that:
- You absolutely need to clear out a HUGE perimeter around the farm to make sure mobs can only spawn in the area you want them to spawn.
- The perimeter around the farm needs to be 128x128. In my case i only cleared out like 50x50 which is by far not enough and the main reason i got extremly low spawn rates compared to JL's video.
- In MC 1.7 and before it is extremly important to notice that the LC Value (as seen in the debug screen) has a huge impact on the farm and spawning behaviour. The LC Value saves for the given chunk how huge the player has builded in this chunk ever since creation of the chunk. For example you go in newly generated terrain at Y = 50 the LC Value will be 50. If you build a 10 high tower on that place the LC will go up to 60. Note that to have good spawning behaviour your LC value needs to be as low as possible.
- Explanation why the LC Value needs to be as low as possible: When MC trys to spawn a Mob in a given chunk, it only will try to spawn it in the area of the chunk under the LC Value. So, if there are several chunks around your farm with a high LC Value, the higher the chance is, that mobs outside of your farm will spawn, because the given chunk actually has more blocks to spawn mobs upon.
- There also is a mobcap on each MC server. So, if you are alone on the server the complete Mobcap will only be taken by you. If there are more players on the server and they even are in different regions, than statistically each player would get halve of the mobcap which means getting halve of the mobspawns.
- There also is a possibility that mobs will be spawned at the edge of the 128x128 perimeter and not despawn instantly due to a bug / feature. JL told me that when a mob is spawned directly at the edge of the 128x128 perimeter and it touches the end of the render distance the game will put this mob into a "sleep" mode thus stopping rendering it. This however causes the mob to still count to the server mobcap while not despawning. Which means it lowers your spawn rate.
This are the reasons i remember, actually JL has told me far more. I convinced him to post a video on that topic on youtube and explane the topic far more in details. The video will come soon from him.
Hope this helps somebody.
Best Answer
This is an awful, ancient design that never worked well and as time progressed, only got worse. It only somewhat works when placed high in the sky and almost doesn't when built on the ground level.
First off, mobs spawn within 128 block radius around the player, so if there are any unlit spaces under ground, mobs will spawn there, and only rarely despawn randomly. That means very few mobs will spawn inside the spawner. Then they must walk at random (rare behavior) into the water channels, and then - unlike in early versions of Minecraft - they'll fight against the current not to fall to their death, and so will only fall when pushed by other mobs in the same stream.
You can get somewhat reasonable (still lousy) drop rates out of this design if you place the kill platform at least 128 blocks above land level (spawn platform accordingly higher; I recommend building over water, reduces chances of death from falling) or at the very least moving the player's afking spot 127 blocks (no higher; otherwise all mobs will despawn!) above the kill platform. Alternatively, with sufficient amount of patience, you can light up ALL the spawning spaces within 128 blocks from the killing floor (...and it's a herculean task) and you'll start seeing reasonable spawn rates. Which will still keep declining as your spawner fills up with spiders congregating under the roof and filling the mob cap.
But what I'd really recommend doing instead is a modern, efficient design like Ilmango's dispenserless.