Intelligent Forwarding Operations

Layer 2 vs. Layer 3

• Routing tables are populated by routing protocols (or admins)
• MAC address tables are built via observation

How to Populate the Routing Table

• Interfaces
  • The first and most highly regarding path
• Static Routes
  • Basically gives you the direction
  • Does nto account for accidents in the way through (does not react to changes in the topology)
• Dynamic Routes
  • If there is a problem in the path, we can detect that and change our decisions based on events that happened our conditions.
• Policy Based Routing (PBR)
  • Effectively taking a policy and using that policy to make a better formed decision.
  • A lot of times we will filter from the source address
  • In traditional routing we take a packet and we look at the Destination IP
  • With PBR, we are looking at the packet and we are applying a policy which can be an ACL (an if condition)
    • Permit or deny
    • Define what should be protected like for IPsec
      • If its permitted we encrypt, if its denied we drop (for example)
  • Typically part of a two step process.
    • If you see packets that match these criteria may be forward them a little bit different.

Control Plane Operations

• Bringing in criteria from other devices

• RIB (Routing Information List)

  • CPU Based Operations vs. ASIC Based Operations

• With ASICs as traffic peaks, your CPU will be barely affected.

• CPU utilization

  • Spike when doing route recalculations
  • Generating IP tunnels, etc
  • Forwarding logic
  • Should come back and idle down little bit

• Interface utilization

  • Not necessarily tracks directly to what your CPU is doing.

Different Tools

• Interior Gateway Protocol (IGP)
  • Runs internally
  • OSPF/EIGRP
• Exterior Gateway Protocol (EGP)
  • Anything you want so long as its BGP (Border Gateway Protocol), which is the routing protocol of the internet.