When your primary site fails, you need somewhere to run. DR sites come in three temperatures.
Cold site: Empty facility with power and cooling. Bring equipment when disaster strikes. Cheapest but slowest. Days to weeks.
Warm site: Some equipment installed but not running production. Hours to days.
Hot site: Fully operational duplicate with continuous data replication. Minutes to hours. Most expensive.
For network: Keep spare gear at the DR site, pre-install cabling, have configs ready, and test failover quarterly.
Choose based on your RTO. -hour tolerance? Warm works. -hour recovery? You need hot standby.