IPv6 is not an upgrade but a
transition. IPv4 and IPv6 are not interoperable directly.
Sadly because it is not interoperable it's not easy to transition, operators must support dual networks, IPv4 and IPv6 for the transition period because if the target website is not reachable on IPv6 it has to use IPv4. This led to many connectivity problems and kept early adopters away. No major websites supported it initially, but it was a necessity and so many major companies like Facebook,
Google etc switched on IPV6 connectivity on a day called "World IPv6 Day". After that not many websites have dual-stack connectivity, there are no reliable metrics for the same.
Cloudflare, Akamai and other CDN's now support single button IPv6 but it still has to be turned on by website owners.
Because there are not many websites, the internet operators worldwide hadn't adopted IPv6. Not to mention maintaining and upgrading all hardware
routers and switches to handle IPV6 address space. They also cannot blackhole content with NAT and CGNAT, some other security issues. Mobile operators worldwide have a different problem, the addresses needed to provide mobile communications is far too costly in time when IPv4 addresses are over. So they kicked off transition to cheap, nearly free IPv6 withNAT64 Translation and other techniques to communicate with IPv4 only sites.
APNIC Allocates IPV6 to asia-pacific region, and they give away addresses easily. It's assumed BSNL have address space likely in 2001::/ ranges. Newer allocations are from 2400:/12 address space for Asia-Pacific, 2600::/12 for North America and 2a00:/12 for Europe. This is why all Airtel, Jio etc address starts with 240___.
BSNL is one of the early ones to claim they will launch IPv6 as early as 2011. As with everything else in BSNL it never materialised. They lack political will (within organisation, not politicians I mean), necessary technical understanding etc at the higher levels of management to pull it off. It also means they need to replace millions of customer modems and heavy network infrastructure for what is considered as little benefit. It is also very tricky to route traffic in the backbone, and since BSNL is primarily used by government rather than consumers, it is a very risky endeavour.
In my opinion, BSNL cannot salvage it's operations, either mobile or broadband. There's too much baggage, you know it when they send old linemen trained to diagnose telephone connections for broadband. Who has no clue of any digital communications, and only makes sure the SNR in modem is acceptable. It's not gonna work.
Sorry for not directly answering as to why BSNL is not IPV6, it is simply
too complicated FOR BSNL STAFF. IPV6 is complicated, but people are trained on it, not BSNL staff.
