I don't intend to sound offensive but was it really that necessary to enable 1.11 clients to connect? Optifine for it is not out, neither are most Resource Packs, and most people stick with 1.9 / 1.10. I just hope we won't stay in 1.9 forever, it's been two versions of MC right now, they're pretty small separated but when counted together they have quite a big amount of features.
Minecraft PC IP: play.cubecraft.net
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If you don't want to update to 1.11 (for whatever reason, Optifine, etc) then you don't have to. But by supporting all three more people can connect.