The Anycast IP (IP) Resilient Hashing (RH) feature enables the customer to define sixteen IPv4 and sixteen IPv6 ECMP routes to always be modified in a resilient fashion. Resilient ECMP route modification means that, when a next hop is added to the ECMP route, then only a small number of existing flows are moved to the new next hop. When a next hop is removed from the ECMP route, then only the flows to the removed next hop are moved to the other next hops. The flows that were previously hashed to still-working next hops are not moved.
The Anycast IP Resilient Hashing feature works in concert with the IP Resilient hashing feature, which is enabled using the ip resilient-hashing command. If IP resilient hashing is disabled, then the network administrator can still add routes to the IP Anycast RH table, but the changes to these ECMP routes are not resilient.
If customers are unable or unwilling to add routes to the Anycast IP RH table, then they can still enable the IP Resilient hashing mode and benefit from that feature. Some route modifications can be done resiliently without adding the routes to the IP RH table, but some route modifications are not resilient. The customer can assess how well the network handles various failure scenarios by running the network failure tests and using the dev hapiBroadL3DebugNonResilientShow command to see how many ECMP route changes were resilient and non-resilient, and which ECMP routes were changed non-resiliently.
