Comparing underlay failure behavior

The diagram below shows network behavior under default aliasing (left) versus Anycast aliasing (right).

Figure 1. Underlay failure: default aliasing versus Anycast aliasing
  • Default aliasing mode: When an underlay network failure occurs, in-flight packets may path hunt until the underlay network converges. If the underlay uses eBGP and the spines share the same ASN, in-flight packets are dropped.
  • Anycast aliasing mode: When an underlay network failure occurs, in-flight packets go directly from Spine1 to Leaf2. Therefore, convergence is faster and more efficient than in the default aliasing mode.