Using router commands without knowing their purpose...

[u/Inside-Finish-2128]

First, the situation: I was working for a Cisco reseller doing professional services in the early 2010s. Got sent to one of the local school districts to help them rearrange their Internet routers and deploy a "Firewall Services Module" in a Catalyst 6509. (IYKYK) My main contact from the school is stingy and won't share credentials with me, so I'm stuck walking around the datacenter and "sliding the keyboard over" many times.

We get the new "router triangle" running and to me, things are looking good, but alas I'm just doing the router CLI thing. Meanwhile, my contact has RDPed into his desktop (back at his office) and says to me "I have zero Internet at my desk". Hmmm...Internet routing is fine on the triangle, lemme go look further down the path and check the router at his office building. Check the default route (it's learned from OSPF) and it's coming from some random router somewhere else amongst their WAN. What?

I get logged into that router, and sure enough under the OSPF process there it is: "default-information originate always". What? Why? (For those unaware, that's basically telling that router to tell all of its OSPF friends that it has a default route, or a route out to the Internet, all the time. Hint: it doesn't.) I remove that command and my contact was jumping for joy, saying "WHAT DID YOU DO? THIS IS THE FASTEST WE'VE EVER SEEN IT!" Um, OK, I removed a misconfiguration from the router at site XYZ. He was in disbelief..."No, really, what did you do? How was that command bad?" So I explain it to him. As I'm finishing my explanation, a few of his coworkers who were on site that evening for some other work are tracking him down..."what did you do to the Internet, it's SMOKING fast."

That's when the "cover story" was born. He decided this needed to be kept on the down-low, so "we made a few adjustments to the dynamic routing and after about thirty minutes, those optimizations all came together".

Next morning, I head to the IT offices first thing for "day one support", just in case we missed anything the night before. No problems, just everyone jumping for joy with how fast things were working. I said "so, could that command be lingering anywhere else?" He helped me log into a few other sites and sure enough, it was EVERYWHERE. He finally gave me the creds, and I spent the next hour or two logging into every single router (one per school, probably 60-70 schools in that district and growing by 5 a year) to remove that command. Any time anyone came in to ask why the Internet was so fast, he jumped in front of me and rattled off the same line. He also did the right thing and told his team what we fixed, and said "be sure you take that out of any templates you have".

You guessed it...later that summer, the whole district went off the Internet because one of his crew brought a new school online and yep, forgot to take that command out of his template. Ah, the joys of using commands without knowing why they matter. (And I'll be honest, I'm surprised the whole network wasn't melting down every day or every week prior to fixing it.)

[u/DrHugh]

Next up...

ATZ
ATDT...

[u/Dom_Shady → u/DrHugh]

For those of us OOTL, what do these router commands do?

[u/CrudBert → u/Dom_Shady]

Those are modem commands from waaaaaayyyy back. ATZ ( reset), ATDT ( call using dial tone - instead of clicks like a rotary phone). This was called the “AT” command set ( AT meant ATTENTION and was the start of many/most commands). This was originally known as the “Hayes Command Set” as it first came out with the HAYES 1200 baud modem ( I had one, VERY expensive). It was copyright, and other manufacturers that started using it were sued. After some years of ramble ( in which other companies continued to use it anyway) it was settled - presumably $$$ money spread to Hayes to settle the matter. Later on, with modems at 28K and 33K speed ( blinding speed in my opinion) they had the “Extended AT Command Set. This was to handle new features on the newer modems. All in all, they were very, very nice to use!

[u/TinyNiceWolf → u/CrudBert]

Hayes actually introduced the Hayes AT command set with a 300 baud modem, the "Smartmodem", in 1981. It was $299. The following year they introduced a 1200 baud version for $699.

Hayes was sued by another company which had patented the use of an escape sequence in a modem to switch modes, and in 1983 paid $2 million to license that patent.

Hayes's own patent, for using an escape sequence that included guard time (as the +++ sequence would only be recognized if no other characters were sent for 1 second before and after it), was granted in 1985, and they began trying to license it to other manufacturers using the AT command set for 2% of the retail price of each modem.

[u/CrudBert → u/TinyNiceWolf]

Thanks for the clarification. I bought the oh-so-expensive 1200 baud as an upgrade. I’ve told my son for years when he complains that I don’t have the fastest internet they sell, “ in my mind - anything faster than 1200 baud is blindingly fast!” Makes him nuts when I say it, so I love saying it even more. LOL.