I am using the latest Forge build (1.7.2-Forge10.12.0.1046) with no other mods installed. I am using the defalt Minecraft launcher. Here is my fml-client-latest.log: http://pastebin.com/gDpag5fp.
I usually have to play Minecraft through a proxy to get around an Internet block. I use a program called proxychains to connect to a SOCKS proxy. To play Minecraft through the proxy, I start the launcher with "proxychains java -jar minecraft.jar". With vanilla Minecraft, this works fine, and I am able to connect to and play on servers with no issue. However, when Forge is installed, I am not able to connect to any servers. All of the servers in my multiplayer menu say "Can't connect to server", and trying to connect to one failes with an "io.netty.channel.ConnectTimeoutException" (http://pastebin.com/s7snj53x).
This is what is outputted to the console when I click on the multiplayer menu without any mods installed, and with Forge installed: http://pastebin.com/smfdaAEp (The DNS-request lines and similar things are added to the log by proxychains).
This problem seems to be limited to connecting to servers, as when I install Liteloader and the VoxelCam mod (http://www.minecraftforum.net/topic/1999989-172-liteloader-voxelcam-minecraft-screenshot-manager-uploader-and-editor/), I am able to use VoxelCam to upload screenshots to Imgur, while still being unable to connect to any servers.
Any suggestions?