Common operational misconceptions

Andreas Echavez andreas at
Thu Feb 16 20:27:08 UTC 2012

I'm surprised I haven't seen QoS mentioned! If you're teaching college
students, you might want to go over stuff that directly relates to what
they're doing at home, or misconceptions they might make in a small
WAN/ISP environment.

*Why disabling ICMP doesn't increase security and only hurts the web* *(path
MTU discovery, diagnostics)
*How NAT breaks end-to-end connectivity (fun one..., took me hours to
explain to an old boss why doing NAT at the ISP level was horrendously
*Not to be afraid of ACLs on an edge router. Understanding what
does/doesn't affect cpu utilization
*Layer 3 Switch vs Router. Old concepts like switch vs router need to be
*When vendors and numbers lie ;) aka *oversubscription*!
*MAC is not security
*Irrelevant security concepts (smurf attacks, ping of death). More focus
should be on real modern day security concerns, like layer 7 exploits,
router software 0days, VLAN hopping, and UDP floods and BGP spoofing. This
might be a good place to explain why downloading IOS firmware from
thepiratebay is a bad idea :)

This is just coming from a sysadmin who likes to play with network gear and
once endured college networking classes.


On Wed, Feb 15, 2012 at 1:47 PM, John Kristoff <jtk at> wrote:

> Hi friends,
> As some of you may know, I occasionally teach networking to college
> students and I frequently encounter misconceptions about some aspect
> of networking that can take a fair amount of effort to correct.
> For instance, a topic that has come up on this list before is how the
> inappropriate use of classful terminology is rampant among students,
> books and often other teachers.  Furthermore, the terminology isn't even
> always used correctly in the original context of classful addressing.
> I have a handful of common misconceptions that I'd put on a top 10 list,
> but I'd like to solicit from this community what it considers to be the
> most annoying and common operational misconceptions future operators
> often come at you with.
> I'd prefer replies off-list and can summarize back to the list if
> there is interest.
> John

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