1.1.b Identify Cisco express forwarding concepts

1.1.b Identify Cisco express forwarding concepts

1. CEF offers the following benefits

   • Improved performance
   • Scalability
   • Resilience
   • Control Plane - Data Plane

2. 1.1.b [i] RIB, FIB, LFIB, Adjacency table

   • Routing Information Base (RIB): maintain the network topologies and routing tables.
   • Forwarding Information Base (FIB): FIBs are the best routes
   • Label Information Base (LIB): It is used by the label distribution protocol for mapping the next hop labels.
   • Adjacency Tables: Layer 2 next-hop addresses for all FIB entries.
   • CEF - takes fast switching a step further by introducing the FIB and Adjacency tables into the equation

3. 1.1.b [ii] Load balancing Hash

   • default in IOS is 4 entries; BGP is one entry (best); maximum number of paths that can be configured are 6
   • Per-destination mode or per-session
     • Preserves packet order
     • Original Mode
     • Universal (default)
     • Tunnel
   • Per-packet
     • packets may arrive out-of-order
     • Round robin
   • hash function source and destination IP addresses and a unique hash ID 16 hash buckets.
   • Per-port

4. 1.1.b [iii] Polarization concept and avoidance

   • CEF polarization
     • same hash algorithm and same hash input
     • Equal-Cost Multi-Path (ECMP) link for ALL flows
     • universal algorithm was developed where a 32-bit value
       • Hash function is known as universal-ID
     • alternate between default (Source IP and Destination IP) and full (Source IP + Destination IP + Layer 4 ports) hashing inputs
   • Avoidance
     • different load balancing algorithms across different routers in the network
     • universal algorithm