TOI Author

Class Based Forwarding (CBF) is a way of steering IP traffic into specific tunnels based on the ingress DSCP values. Arista already supports class based forwarding today, and the details about the existing support can be found in this CBF TOI. CBF is implemented in the hardware using an override model. As always, forwarding for an ingress IP packet begins with a lookup in the L3 FIB, which returns a default Forwarding Equivalence Class (FEC) to use. If CBF is enabled, an additional lookup is made in order to determine whether traffic associated with that default FEC and with the ingress packet’s DSCP should be steered into an SR Policy tunnel/RSVP-TE/Flex-Algo tunnel. In network deployments where unique (gateway) endpoints are large, the default FEC combinations generated by controller based on these endpoints can be a lot, and the existing approach with the override model using hardware’s TCAM resource doesn’t scale well, given that this resource is limited in nature. To overcome these scale issues, we have developed an alternative approach for CBF that is based on VRF Selection Policy.