使用SSH遇到ssh_exchange_identification错误

ssh_exchange_identification: read: Operation timed out
debug1: key_load_public: No such file or directory

$ ssh -T -vvv git@github.com
OpenSSH_7.6p1, LibreSSL 2.6.2
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 20: Applying options for *
debug1: /etc/ssh/ssh_config line 48: Applying options for *
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to github.com port 22.
debug1: Connection established.
debug1: identity file /Users/yuzefeng/.ssh/id_rsa type 0
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yuzefeng/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6