On a network with broken IPv4 connectivity and fully working IPv6, telegram for android repeatedly tries to connect using IPv4 and never attempts IPv6.
Telegram for iOS/macOS tries IPv4 first, and eventually retries using IPv6 causing a significant connection delay.
This is a common scenario, as ISPs implement unreliable CGNAT to work around IPv4 address shortages. The CGNAT gateway here is slow and unreliable, its addresses often blacklisted. IPv6 is fast and reliable.
Due to the CGNAT, the p2p calls option will NEVER work over IPv4, whereas it can be fast and reliable using IPv6 as the phone has a global routable address.
Most apps implement "happy eyeballs" and will try IPv6 first, only failing over to legacy IPv4 if IPv6 is unavailable. Telegram should behave this way too.
Steps to reproduce
1, configure a network with an ipv4 default route that cannot reach telegram's servers and a fully working ipv6 route
2, try to connect to telegram
3, telegram repeatedly tries ipv4 and never tries ipv6
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