300-135 TSHOOT Quick Study Notes: ping, telnet, SDM Templates, Switching Methods, CPU Operation

Useful ping command options [default]:
  • size: bytes per datagram [100]
  • repeat: ICMP echo messages sent [5]
  • timeout: seconds to wait for ICMP echo reply [2]
  • source: IP of ICMP messages [exit interface]
  • df-bit: if frame can be fragmented (0) or not (1) [0]

Meaning of ping output characters:
  • ! = receipt of reply
  • . = time out while waiting for a reply
  • U = source quench (destination too busy)
  • M = could not fragment
  • ? = unknown packet type
  • & = packet lifetime exceeded

  • You can specify an alternate port number in the telnet command to check if a particular service is running at the destination IP
  • Example: Open message indicates that is running HTTP (TCP port 80)

R1#telnet 80
Trying ... Open

SDM templates:

Switching methods:
  • process switching: every packet is handled by the CPU
  • fast switching: first packet is processed by the CPU; subsequent packets are forwarded based on fast cache
  • CEF: packets are forwarded in data plane based on prebuilt FIB and adjacency tables

CPU operation:
  • two distinct functions: run IOS processes and send/receive packets to/from switching hardware
  • do show processes cpu [sorted] for details
  • pay attention to total CPU utilization vs. interrupt level usage
  • see: Troubleshooting High CPU Utilization