Overview

CBF uses dedicated layer 2 interfaces, called CBF interfaces, that are configured at the top of interface columns for SMDS tunnel connections. CBF interfaces used in connection-based forwarding are analogous to IP interfaces used in IP routing.

A CBF interface runs over an SMDS trunk interface. Only one CBF interface is permitted per SMDS interface. The CBF interface forwards SMDS traffic among SMDS trunk interfaces.

CBF provides a simple mechanism for forwarding non-IP traffic directly between E-series devices. It is a method of forwarding frames in which forwarding decisions are based only on the identity of the ingress interface. In particular, no part of a packet's contents is used to determine how a packet should be forwarded.

CBF forwards frames along connections configured between pairs of interfaces. Frames received on a connection's ingress interface are forwarded directly to that connection's egress interface. The packet is transmitted from ingress to egress forwarding interfaces as the raw layer 2 payload received from the layer 2 interface. Both the ingress and egress interfaces are SMDS-encapsulated and have CBF interfaces associated with them. Once the connection between the ingress and egress interfaces is made, traffic begins to flow.