Actually your question is a bit vague and lacks critical detail. Part 2 can be easily found in lots of places and even on Server Fault with a simple search and a bit of rummaging through the results.

The first part lacks critical detail.

• How are you trying to connect from the client to ServerB:3306 via server A presumably?
• Have you enabled routing on server A ?
• Have you tried to connect from server A to Server B 3306 was it successful or not?
• When you try to connect from the client to ServerB:3306 what error messages do you see ?
• Have you tried using something like tcpdump to trace the connection through the network ?

People have just downvoted your question based on what they can see and that's not great.

Downvoting isn't an unfriendly action it's a reaction to poor quality.

You are way overreacting to this.

Actually your question is a bit vague and lacks critical detail. Part 2 can be easily found in lots of places and even on Server Fault with a simple search and a bit of rummaging through the results.

The first part lacks critical detail.

• How are you trying to connect from the client to ServerB:3306 via server A presumably?
• Have you enabled routing on server A ?
• Have you tried to connect from server A to Server B 3306 was it successful or not?
• When you try to connect from the client to ServerB:3306 what error messages do you see ?
• Have you tried using something like tcpdump to trace the connection through the network ?

People have just downvoted your question based on what they can see and that's not great.

Downvoting isn't an unfriendly action it's a reaction to poor quality.

You are way overreacting to this.