It is probably in bridge mode and the firmware is locked into that particular state. If you need to access the
router's web admin access page set your PC/laptop to 192.168.1.254, sub-net 255.255.255.0 and use your browser to navigate to the page.
Also remember I had this experience where the Admin user name password at the bottom of the router was only a user with no admin rights. These guys, at least the
Tata Sky idiots secretly flashed the router with a custom firmware from
Nokia which disables the admin profile and creates a new one in its place. You cannot make any changes to the router without the 'new' admin level login ID and password.
I can imagine Airtel does the same because these units are only sold to ISPs and never via retail channels. So they receive no support from Nokia/Alcatel Lucent including no firmware updates.