Thomas A. Limoncelli is an internationally recognized author and speaker. He is best known for his books The Practice of System and Network Administration (with Christina J. Hogan and Strata R. Chalup), Time Management for System Administration and The Complete April Fools RFCs (with Peter J. Salus). Read more about Tom and his books at Everything Sysadmin.
Often I've come to a site and been asked to clean up someone else's mess. When I look at their design and look at the mess they're in, I realize that someone decided to save a buck by coming up with a [network] design that isn't supported by the vendor. [The design] isn't supported for a reason: [it's] breaking some rule.
Sometimes the mess isn't a major mess. [In these cases a company] called the vendor and asked for support, [but the vendor said] they can't help [because] the [network] design isn't uniform. [For that reason] a lot of vendors these days will be involved in any kind of major [network] design, and any recommendation they make
The number one thing you want to hear when you call a vendor support line is, "Ah yes, that's our standard design. Let me help you right away," and not, "You did what? Let me see if I can get permission from my manager to see if I can replicate that in my lab and see what's wrong."
Some [network design] problems I've seen are:
Complex routing structures where routing protocols are translated from one to another and then back again.
Ad hoc solutions to get connectivity to some distant part of the building.
Gateways between different protocols because there was a political issue in the company and they couldn't decide on just one, so they decide to support both protocols and have some kind of translator.
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