Checking the Status of Major Routers Switches and Firewalls
The final step in characterizing the existing internetwork is to check the behavior of the internetworking devices in the internetwork. This includes routers and switches that connect layers of a hierarchical topology, backbone routers and switches, and routers, switches, and firewalls that will have the most significant roles in your new network design. It's not necessary to check every LAN switch, just the major switches, routers, and firewalls.
Checking the behavior and health of an internetworking device includes determining how busy the device is (CPU utilization), how many packets it has processed, how many packets it has dropped, and the status of buffers and queues. Your method for assessing the health of an internetworking device depends on the vendor and architecture of the device. In the case of Cisco routers, switches, and firewalls, you can use the following Cisco IOS commands:
• show buffers. Displays information on buffer sizes, buffer creation and deletion, buffer usage, and a count of successful and unsuccessful attempts to get buffers when needed.
• show environment. Displays temperature, voltage, and blower information on the Cisco 7000 series, Cisco 7200 series, Cisco 7500 series routers, and Cisco 12000 series Gigabit Switch Router.
• show interfaces. Displays statistics for network interface cards, including the input and output rate of packets, a count of packets dropped from input and output queues, the size and usage of queues, a count of packets ignored due to lack of I/O buffer space on a card, CRC errors, collision counts, and how often interfaces have restarted.
• show memory. Displays statistics about system memory, including total bytes, used bytes, and free bytes. Also shows detailed information about memory blocks.
• show processes. Displays CPU utilization for the last 5 seconds, 1 minute, and 5 minutes, and the percentage of CPU used by various processes including routing protocols, buffer management, and user-interface processes. (The show processes cpu and show processes cpu history commands are both useful variations of the show processes command.)
• show running-config. Displays the router's configuration stored in memory and currently in use.
• show startup-config. Displays the configuration the router will use upon the next reboot.
• show version. Displays software version and features, the names and sources of configuration files, the boot images, the configuration register, router uptime, and the reason for the last reboot.
You can also use SNMP to check the health of an internetworking device. The following is a list of useful performance variables in the Cisco private extension to the Internet standard Management Information Base II (MIB II):
• BusyPer. CPU busy percentage in the last 5-second period.
• AvgBusy1. 1-minute exponentially decayed moving average of the CPU busy percentage.
• AvgBusy5. 5-minute exponentially decayed moving average of the CPU busy percentage.
• LocIfInputQueueDrops. The number of packets dropped because the input queue was full.
• LocIfOutputQueueDrops. The number of packets dropped because the output queue was full.
• LocIfInIgnored. The number of input packets ignored by the interface.
• BufferElMiss. The number of buffer element misses. (You can also check misses for small, medium, big, large, and huge buffer pools.)
• BufferFail. The number of buffer allocation failures.
To analyze a device's health, you need to check the variables listed above on a regular basis over a few days. To get a precise and complete portrayal of performance, a long-term study (lasting a few weeks or months) should be done, using some of the tools mentioned in the next section and in Chapter 9, "Developing Network Management Strategies." (As a network designer, it is probably not your job to do the long-term study. You should encourage your customer to assign network engineers or consultants to the job of proactively studying long-term performance.)
Continue reading here: Network Monitoring and Management Tools
Was this article helpful?