Telnet三种方式：
(1)None
(2)Password:
(3)Scheme:
第一种方式：
[H3C]telnet server enable//开启telnet服务器
[H3C]user-interface vty 0 4
[H3C-line-vty0-4]authentication-mode none
[H3C-line-vty0-4]user-role network-admin
第二种方式：
[H3C]telnet server enable//开启telnet服务器
[H3C]user-interface vty 0 4
[H3C-line-vty0-4]authentication-mode password
[H3C-line-vty0-4]user-role network-admin
[H3C-line-vty0-4]set authentication password simple 123
第三种方式：
[H3C]telnet server enable//开启telnet服务器
[H3C]user-interface vty 0 4
[H3C-line-vty0-4]authentication-mode scheme
[H3C]local-user h3c class manage
New local user added.
[H3C-luser-manage-h3c]password simple 123
[H3C-luser-manage-h3c]service-type telnet