totally beyond me - dunno what dumpmdm command is/does and rolling back firmware to move forwards is more fault points, surely going back to 28 would undo what you've just done? never had problem in 2 years so just leve it I think
Have you simply tried zyad1234 as a password?
The dumpmdm command simply spits out txt in the Telnet session. It changes nothing on the modem.
It gives the current passwords in plain txt, including the unknown Supervisor password.
Rolling back firmware allows you to view the password.
Yes upgrading back to 28 will undo what you just did, but who cares. By that point you have the Supervisor password and there's no more need for the dumpmdm command.
There are other ways to obtain the Supervisor password while on v28 of the firmware.