解决方案

原因：MTU 设置为 9000 ：

# ip add| grep -i eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc pfifo_fast state UP group default qlen 1000
inet x.x.x.x/24 brd x.x.x.x scope global noprefixroute eth0

为两个节点捕获的 Tcpdump 显示正在重新传输长度大于 1500 的数据包。

8 11:13:10.813477 x.x.x.x y.y.y.y SSHv2 87 Server: Protocol (SSH-2.0-OpenSSH_7.4)
9 11:13:10.813678 x.x.x.x y.y.y.y TCP 66 44545 → 22 [ACK] Seq=3850969800 Ack=2311909757 Win=26880 Len=0 TSval=232224817 TSecr=231194452
10 11:13:10.814416 x.x.x.x y.y.y.y SSHv2 1562 Client: Key Exchange Init
11 11:13:10.924128 x.x.x.x y.y.y.y SSHv2 1346 Server: Key Exchange Init
12 11:13:10.963964 x.x.x.x y.y.y.y TCP 66 44545 → 22 [ACK] Seq=3850971296 Ack=2311911037 Win=29440 Len=0 TSval=232224968 TSecr=231194563
13 11:13:11.020996 x.x.x.x y.y.y.y SSHv2 114 Client: Diffie-Hellman Key Exchange Init
14 11:13:11.021435 x.x.x.x y.y.y.y TCP 78 [TCP Window Update] 22 → 44545 [ACK] Seq=2311911037 Ack=3850969800 Win=28032 Len=0 TSval=231194660 TSecr=232224817 SLE=3850971296 SRE=3850971344
15 11:13:11.022944 x.x.x.x y.y.y.y TCP 1562 [TCP Out-Of-Order] 44545 → 22 [PSH, ACK] Seq=3850969800 Ack=2311911037 Win=29440 Len=1496 TSval=232225027 TSecr=231194660
16 11:13:11.228988 x.x.x.x y.y.y.y TCP 1562 [TCP Retransmission] 44545 → 22 [PSH, ACK] Seq=3850969800 Ack=2311911037 Win=29440 Len=1496 TSval=232225233 TSecr=231194660
17 11:13:11.641942 x.x.x.x y.y.y.y TCP 1562 [TCP Retransmission] 44545 → 22 [PSH, ACK] Seq=3850969800 Ack=2311911037 Win=29440 Len=1496 TSval=232225646 TSecr=231194660

为了解决此问题，请在 /etc/sysconfig/network-scripts/ 中的网络配置文件中将各个接口的 MTU 设置为 1500。

问题

尝试通过 SSH 登录时，会话卡住。

添加“-vvv”选项，显示它挂起并显示以下消息：

debug1: expecting SSH2_MSG_KEX_ECDH_REPLY