Configuring Entropy Labels
An entropy label is a special label that enhances a network device’s ability to load-balance traffic across equal-cost multipath (ECMP) paths or link aggregation groups (LAGs). When you configure an entropy label at the ingress device, the transit device use the label to determine a path in place of performing a deep packet inspection (DPI). If the transit device does not support LDP Entropy Label Capability (ELC), the transit device ignores the entropy label and continues to propagate the packet using traditional DPI for load balancing. The entropy label is popped at the penultimate hop device.
An entropy label can be any label value between 16 to 1048575 (regular 20-bit label range). Since this range overlaps with the existing regular label range, a special label called entropy label indicator (ELI) is also inserted in the label stack before the entropy label. IANA assigned ELI label a value of 7. This distinguish entropy labels from other service labels.
To configure entropy labels, include the entropy label at the [edit protocols ldp] hierarchy on the ingress device and include the configured policy in the routing policy.
To enable a penultimate hop device to pop the entropy label, include the load-balance-label-capability statement at the [edit forwarding-option] hierarchy.