JUNOS High Availability

Address Allocation

Intelligent address allocation is arguably the most critical element in controlling the size of the intradomain routing table. While an intelligent addressing scheme is often a byproduct of “good design,” and therefore applicable in “greenfield” situations, it is also an element that can be applied to mature networks. Furthermore, the increasing use of multiple logical networks or service overlays, riding on a single collection of physical routers, means that many more architecture and design opportunities for intelligent address allocation exist than did just a few years ago.

Logical Networks As Design Opportunities

Logical networks as a tool for high availability are covered in detail later in this chapter. However, they do merit some immediate discussion to clarify the previous statements on design opportunity being more than a “greenfield” endeavor.

A logical network is a collection of logical components, including IP addresses, routing protocols, routing policies, virtual LAN (VLAN) tags, and ATM PVCs, that are collected together on a group of physical devices and links. Several years ago, businesses were content to have a single logical construct in their physical network, but this is no longer the case. Service providers and medium to large enterprise networks now commonly have multiple logical networks overlaid on the same physical infrastructure.

A network must have a Layer 2 and Layer 3 addressing scheme, as well as a way to share reachability information ...