It will take a long time to be prompted for the password after input the user name when client login S5720 switch through SSH.

Device version: S5720 V200R011C00SPC200

Analysis SSH debug information finding that it is pending in the calculation of the key phase, the following has nearly 14 seconds of waiting time.

Apr 14 2016 20:20:06.270.3 S5720-52X-PWR-SI SSH/7/NO_INFO:Begin to compute the dh shared key.

Apr 14 2016 20:20:20.230.1 S5720-52X-PWR-SI SSH/7/RECV_PKT:Received ssh2 msg ecdh reply packet.

The device provides three key exchange algorithms: dh_group_exchange_sha1, dh_group14_sha1, dh_group1_sha1。From a security perspective, it is recommended that you use the dh_group_exchange_sha1 algorithm, but it will take a long time. Now network equipment is using this key exchange algorithm.

Apr 14 2016 20:20:06.170.9 S5720-52X-PWR-SI SSH/7/CHOOSE_KEX:Choose Kex algorithm:diffie-hellman-group-exchange-sha1.

The more secure the key exchange algorithm is, the longer the key needs to be calculated, and the different CPU processing power of different device forms may increase the computation time.

There is a command line in the device for customers to choose algorithm with short key calculation time (the corresponding security will also be reduced).