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
TIP:
- 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 10.1.1.80 is running HTTP (TCP port 80)
R1#telnet 10.1.1.80 80
Trying 10.1.1.80 ... Open
SDM templates:
- some switches allow you to change the TCAM memory allocated to different switch features
- optimizing the switch's resources is done by changing the SDM template
- the templates are predefined and cannot be edited
- see: Understanding and Configuring Switching Database Manager on Catalyst 3750 Series Switches
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
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