putty 拒绝连接 是怎么回事

拿出内存卡，在boot下新建一个名叫ssh的文件

As of the November 2016 release, Raspbian has the SSH server disabled by default. It can be enabled manually from the desktop:

Launch Raspberry Pi Configuration from the Preferences menu
Navigate to the Interfaces tab
Select Enabled next to SSH
Click OK
Alternatively, raspi-config can be used:

Enter sudo raspi-config in a terminal window
Select Interfacing Options
Navigate to and select SSH
Choose Yes
Select Ok
Choose Finish

新建个空的ssh文件就行，或者你可能关闭了Ipv6 probe

赞同楼上的观点！