Describing High Availability in Multilayer Switching
High availability: core layer best practices
These best practices are recommended for optimum core layer convergence.
Build triangles, not squares, to take advantage of equal-cost redundant
paths for the best deterministic convergence.
Design the core layer as a high-speed, Layer 3 switching environment
utilizing only hardware-accelerated services. Layer 3 core designs are superior
to Layer 2 and other alternatives because they provide:
Faster convergence around a link or node failure.
Increased scalability because neighbor relationships and meshing are
reduced.
More efficient bandwidth utilization.
When considering high availability in the core, it is assumed that
point-to-point links such direct Ethernet links exist between the core and
distribution and between core devices. Link up or down topology changes can be
propagated almost immediately. With topologies that rely on indirect
notification and timer-based detection such as SONET, convergence is
non-deterministic and convergence is measured in seconds