Before diving into the details of how JUNOS-enabled networks can be managed to promote high availability, we need to examine networks at the architectural level in order to distinguish a high availability network from other networks.
Redundancy schemes are relative to a layered model and can be described with the following line of simple premises:
- Redundant components protect systems
High availability at the system layer is supported by redundant hardware components such as power supplies, interface cards, and processor engines.
- Redundant systems protect services
High availability at the service layer is supported by redundant systems such as routers, switches, and servers.
- Redundant services protect the enterprise
High availability at the enterprise layer is supported by redundant services such as email, VoIP, the Web, and “shopping carts.”
- Redundant enterprises protect free-market economies
Though relevant to the current state of world finances, this premise is beyond the scope of this book.
Each layer in the model can be said to have an associated base cost that represents the price of functionality at that layer. High availability is provided by protecting base functionality with hardware, software, configuration options, staffing, or whatever else is available. In almost every case, adding protection to a layer’s functionality increases the cost of that layer.
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