Frame Forwarding with One DLCI Field
The most significant difference between the two other popular addresses in CCNA Routing and Switching (MAC and IP) versus DLCIs relates to the whole forwarding process. The Ethernet header includes both a source and destination MAC address, and the IP header includes a source and destination IP address. However, the Frame Relay header lists only one DLCI field, and it does not identify a source or a destination, but the PVC.
To get an idea of how the provider forwards a Frame Relay frame, consider the fact that the provider knows the local DLCI used on both ends of the PVC, plus the access links that connect to those routers. For instance, in Figure 13-8, the provider knows that a PVC exists between router ...
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