Describes CEF operation, route programming, forwarding scale, load distribution, and diagnostics. Provides requirements and tasks for configuring and verifying supported forwarding features.
Cisco Express Forwarding (CEF) is a Layer 3 forwarding architecture that uses forwarding and adjacency information to switch IPv4 and IPv6 packets. It supports route programming, hardware scale profiles, and load distribution. CEF also provides operational commands for verification and forwarding diagnostics.
This chapter covers CEF fundamentals, static routes, proactive adjacency resolution, route-scale profiles, shortened IPv6 prefixes, per-NPU hash rotation, and FIB diagnostics.
Cisco Express Forwarding fundamentals
Explains how CEF uses forwarding and adjacency data to provide scalable Layer 3 packet forwarding and covers its operation, supported functions, benefits, and access requirement.
Configuration status of CEF hardware modules
Explains how hardware-module status identifies configured CEF profiles, whether each profile is applied, and whether a reload or commit action remains pending.
Static routes and Cisco Express Forwarding
Explains when static routes provide predictable paths for CEF forwarding and why dynamic routing is more suitable for large or frequently changing networks.
BGP attribute downloads
Explains how downloaded Border Gateway Protocol (BGP) attributes become visible in CEF and how global or local attribute identifiers select a specific installed attribute for inspection.
Proactive Address Resolution Protocol and Neighbor Discovery
Explains how proactive ARP and ND preemptively resolve incomplete Layer 2 next-hop information for CEF routes, reducing first-packet software forwarding and helping prevent resolution failures and traffic drops.
Route-scale profiles
Explains how a route-scale profile reallocates hardware resources to increase IPv4 and IPv6 FIB capacity. Covers capacity changes, classification tradeoffs, configuration, and restoration.
Full-scale longest-prefix-match mode
Explains how full-scale longest-prefix-match (LPM) mode reallocates memory and ternary content-addressable memory to maximize IPv4 and IPv6 route capacity.
Shortened IPv6 routing prefixes
Explains how shortening wide IPv6 prefixes improves LPM memory use and mitigates out-of-resource conditions. Covers operation, platform restrictions, configuration, reload, and verification.
FIB object-ID diagnostics
Explains how FIB object-ID diagnostics expose allocated identifiers in the default and encapsulation-ID tables for targeted forwarding-object troubleshooting and inspection.
Hash rotation for individual NPUs
Explains how per-NPU hash rotation varies path-selection inputs to reduce traffic polarization. Covers the forwarding process, deployment restriction, configuration priorities, and hardware verification.
Unified CEF error counters
Explains how a unified command consolidates FIB error counters for rapid forwarding diagnostics. Covers benefits, debugging guidance, supported hardware, and location-specific or systemwide views.