Cusomer found out that two elements (OSN3500 and OSN1500) periodically disconect from T2000 with period of 2-3 seconds.
Customers T2000 server connect to these two NEs with default user name "root"and password "password". These two NEs have commercial traffic.
Customer IP network is not segmented. No real secuirity politics are used in the customer's network. It is possible to connect to any NE of network through LAN of any customer's branch office easily.
Create new NE account through Navigator with "admin" rights (:sm-add-user:"USERNAME","PASSWORD","admin",enable). You also can do it on T2000. Switch to this new NE user in T2000 for each problem elements.
P.S. If it possible, find the reason why default username "root" is conflicted. Only when reason will be removed you may switch to "root" account in T2000 for these problem NEs. But generally it is not recommended to use the default account "root" to connect NEs.
1) Software problem;
2) Another T2000 server connects to these two NEs with same user name/password;
3) Another equipment with same IP and same user name/password was installed in the customer's network.
Firstly we reset these NEs trough Navigator with software reset. It had no results.
Secondly we tried to find out another user who connected to these NEs through T2000 or another equipment that IP addresse was conflicted with these two NEs. These attempts had no results.
Thirdly we tried to change password of "root" account. It also had no results.
Fourthly Through Navigator we connected to these two problem NEs and created new user with admin rights (:sm-add-user:"test2","password123","admin",enable). Then connect to the NEs through T2000 ander with these new account. Problem was solved.