How Healthy is your Existing Network?

Cisco provides us with a nice starting point for analyzing the health of our existing network as we Plan for redesigns. Check it out:

  • Ethernet segments should not feature a sustained utilization of 40% or higher
  • All Ethernet segments should be switched – no shared segments (hub-based)
  • No WAN links should feature a sustained utilization of 70% or higher
  • Response times should be generally less than 100 ms
  • LAN response times should generally be 2 ms
  • No segments should have more than one CRC (cyclic redundancy check) error per million bytes of data
  • No segments should have more than 20 percent multicast or broadcast traffic
  • For Ethernet segments, there should be less than .1 percent collisions over 5 minute intervals
  • CPU utilization should not exceed 75%
  • The number of output queue drops should not exceed 100 in an hour
  • The number of input queue drops should not exceed 50 in an hour
  • The number of buffer misses should not exceed 25 in an hour
  • The number of ignored packets should not exceed 10 in an hour

Study Existing Network Still

15 thoughts on “How Healthy is your Existing Network?

    1. Sure – a broadcast domain is all of those devices that will hear a broadcast when one is sent. So imagine a PC sending a broadcast into the switch. This will go to all systems in that VLAN. The VLAN is the broadcast domain. A collision domain is all of those devices that might experience a collision on the network. Today we can make that about zero! This is because switches intelligently forward traffic based on MAC address information. So every single port on your switch is a collision domain! This is often called micro segmentation on the network.

  1. Hi Anthony,
    First, I would like to thank you for this interesting topic.
    I have one question regarding (No WAN links should feature a sustained utilization of 70% or higher). does it mean that if I have a 10Mbs internet connection, I should limit traffic to 7 Mbs and at the same time allowing brief peaks exceeding this bandwidth ?

    Thanks,
    Nassim

    1. Yes exactly. Sustained here means pretty much the average, understanding that you will have periods of less usage, and more.

  2. Hi Anthony,

    Just a quick punctualization…when talking about collisions over a 5 minutes interval, it says .1 percent. Is this 1% or 0.1%?

    Thanks

  3. Hi Anthony,

    I´d like to know how could we measure most of the points that are present on this list. I know that using SNMP we could measure bandwidth easily, but how could we measure things like the CRC errors, the multicast and broadcast traffic, collisions and the queue drops.

    Thanks,
    Americo

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