Published on wayland's Computer Stuff (http://computerstuff.jdarx.info)
Cisco Operations Order
By wayland
Created 2008-01-19 06:43

Details the order of operations for a Cisco. This is the most complete list I've seen anywhere, and as you can see, it's compiled from multiple sources.
General Areas Inside Cisco IOS Software
Architecture, posted
Input Compression / Decompression If IPSec then check input Access list
  • QoS Policy Propagation through Border Gateway Protocol (BGP) (QPPB)
  • Input common classification
  • Encryption decryption - for CET (Cisco Encryption Technology) or IPSec
    Check inbound/input access-list
    Unicast reverse path check
  • Input marking (class-based marking or Committed Access Rate (CAR))
  • Input policing (through a class-based policer or CAR)
  • IP Security (IPSec)
  • Cisco Express Forwarding (CEF) or Fast Switching
  • Check input rate limits
  • Physical broadcast: ip helper addresses etc.
  • Decrement TTL - if not already done
  • input accounting
  • Inspection subsystem (firewall features)
    Inbound: NAT outside to inside (global to local translation)
    Routing
  • Handle the router alert flags in the IP header
  • Search for outbound interface in the routing table
  • Policy routing
    Routing
    Web cache redirect
    Output Outbound: NAT inside to outside (local to global translation)
  • CEF or Fast Switching
  • Output common classification
  • Encryption Crypto (check map and mark for encryption)
    Check output access-list (packet filters)
    Inspection subsystem final checks (firewall features)
  • Output marking
  • Output policing (through a class-based policer or CAR)
  • Queueing (Class-Based Weighted Fair Queueing (CBWFQ)
    and Low Latency Queueing (LLQ)), and
    Weighted Random Early Detection (WRED)
  • TCP intercept processing
    Encryption

    On the inbound path, a packet is classified before it is switched. On the outbound path, a packet is classified after it is switched.

    Note: Input Network-Based Application Recognition (NBAR) happens after ACLs and before policy-based routing.


    Source URL: http://computerstuff.jdarx.info/content/cisco-operations-order