The Two Principles Of Troubleshooting

  1. Never trust someone else’s configuration.
  2. Don’t trust your own configuration.

But in all seriousness. If you’re migrating configuration, this would be a good place to start:

  • Check all your IP addresses are consistent.
  • Check your masks are consistent.
  • Check your interfaces are correct.
  • If you’re working with peers, check your IP addresses for the peers are correct.I mean all 4 octets. Not just the last one, or two, or three. ALL FOUR. If it’s v6, then FML. Bite the bullet and write a script.
  • Is there a naming convention to follow? There’s a temptation when migrating to stick with the old name, but new devices may require a different convention is adhered to. Reasons for this range from the whimsical to the valid.

If you’re coming up with something new, and it involves addressing new interfaces then start with this:

  • First check your IP allocations are correct. By this, I mean check if you have any hierarchy or ordering. For example, do you reserve addresses by site, geographic location or application? If you do, then make sure these are consistent with what you’ve planned.
  • Is your addressing valid? i.e: Are the subnets and host addresses you’ve assigned correct? For example, make sure you’ve not assigned subnet addresses to hosts. This is an important detail to keep in mind when you’re allocation away from the border of an octet (/25-32s).
  • Is there a naming convention to follow?

Apart from this, in general when you’re using a scripted or “run-booked” change and you’re filling it in then try this for starters:

  • Make notes first.
  • Delete all the example, or pre-filled configuration that doesn’t apply to you to prevent human error.
  • If it’s a large change involving multiple stages – for example, you pre-configure interfaces – then track your work. If you’re using Excel for your runbooks then consider using colours to tag what’s complete (green for done, red for not done, or not being done, yellow for things that need checking etc.).
  • If you’re going to work with technologies you’re not familiar with, then consider educating yourself on them in order to troubleshoot accurately.

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