Redundancy is built in levels, from simplest to most robust:
- 4G/5G backup: automatic failover to mobile. Enough for a branch office’s day-to-day.
- Dual fiber access: two links — demanding physically separate paths (distinct building entries): two fibers in the same trench fail together at the first backhoe strike.
- Dual carrier: also eliminates a failure of the carrier’s own network.
- BGP multi-homing: with your AS and your addresses announced to both carriers — the only level where your public IPs survive the complete loss of one provider.
Without your own AS, the alternative: a carrier present at both your sites, announcing the same pool on both sides. And don’t miss the classic blind spot: DNS egress and the firewall must follow the failover, or the network redundancy is useless.