Describes the Resilient Hashing Feature
SLX devices use Equal Cost Multi Path (ECMP) distribution of traffic within the group. A hash value of the packet is calculated (based on the packet headers) and then a modulo of this hash value is calculated based on the number of paths in the ECMP group. The packet is then directed to the path with the calculated modulo value.
However, when the number of available paths in a ECMP group changes, either due to a link not being available or when a link come backs up, the modulo needs to be calculated again to choose the new paths for existing flows. This change in path mapping might cause disruption in traffic flow.
Resilient Hashing is a feature that ensures that there is minimal disruption in traffic flow when there is a disruption due to link failure or link addition. Resilient Hashing is supported for L3 traffic routed using BGP (support for both IPv4 and IPv6 traffic) and Static Routes.
Resilient Hashing is not supported for L3 traffic forward by IGP routes (OSPF, OSPFv3, and ISIS). It does not support cases where a new nexthop gets added to an existing set for both BGP as well as Static Routes.