Why Is CEF Needed in MPLS Networks

or the CEF table, the outgoing packet can be a labeled packet or an IP packet. Figure 6-1 shows the difference between a lookup in the CEF table and in the LFIB.

Figure 6-1 Lookup in CEF Table Versus Lookup in LFIB

Lookup in CEF Table

Lookup in LFIB Table

Lookup in LFIB Table

When an IP packet enters the router and the packet is forwarded out of the router labeled, CEF needs to label the packet with a label stack. That label stack can have any number of labels in it. CEF is the only switching method in Cisco IOS that can label an incoming IP packet and forward it. (This is the IP-to-label forwarding case.)

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