Yeah - code rewrites are generally a thing to be avoided since the requirements of older production code is typically not fully documented, even if it originally had been. Production code accumulates bug fixes, performance tweaks, special cases, additional requirements, etc, with documentation and test suites not always being updated in sync.
Your rewritten codebase will presumably look much cleaner and more maintainable that what it's aiming to replace, but it's easy to miss the purpose/necessity of all of the old "cruft" which need not be just poor coding but rather later enhancements not anticipated by the original design whose implementation was therefore crufty.
Does anyone here work at Cisco, and have any insight as to why a rewrite is considered necessary and might be expected to succeed?
A rewrite is a slam dunk for any decent frontier AI. It has a penchant for maintaining API/etc contracts to a fault in the absence of instructions to the contrary. It can easily validate its work and loves building exhaustive test cases. You can tell it to get 100% code coverage if you want. It will laborously accurate document every accumulated edge case and help you find a better overall cohesive structure.
A rewrite has historically been a huge mistake in many situations, some of which I've personally had the agony of witnessing firsthand, powerless to stop it. But AI completely changes the calculus because it doesn't waste significant developer time or energy crawling back to the previous working state, it just does it while you go get coffee. And this I've found to be a huge benefit, that I can continue making my codebases nicer to work with and better documented/integrated with bugs stamped out for free. There are upsides to a rewrite, and they're now much more likely to be worth it as the downsides are automated away.
The entire point of a rewrite is to get rid of the behaviour you don't want, while you keep the behaviour you do want. Consider the pathological case: Rewriting your FORTRAN codebase in Rust would obviously be useless if you had to reimplement every bug in the rewrite.
An LLM doesn't have enough context to know what you so and don't want. If you give it call logs for every function that was called and how, maybe, but a seasoned engineer will have more context around what the company needs.
Not necessarily, a rewrite can just move to a language that's easier to maintain (off C / cobol).
Honestly though, it's pretty clear the AI rewrites work, we have a ton of high profile examples. It's just a holdover attitude about rewrites from before AI. In reality, AI is going to make the code better when it rewrites
Defining the legacy bugs and porting them as features during the rewrite is actually one of the most difficult parts of enterprise rewrites.
You don't get to pick what parts of the API you're porting during something like that, it has to work the same or some of the ecosystem around it will break.
If this was true then Python would already have been rewritten to be GIL-free, and the entire ecosystem of Python packages would have been rewritten to respect its API.
Absence of evidence is not evidence of absence! We're on this thread because Cisco is sponsoring piles of tokens at the problem. No such megacorp sponsor exists for this problem for Python. The megacorps have decided not to sponsor that specific problem.
I'd even argue AI is better for maintaining/moderninzing existing code than writing it, just because there is so much less input from developer about architecture it requires, as it has it in the code itself.
But there is pretty big risk of false positives and negatives; some "bugs" are design decisions that were not documented well/at all, and inevitably some new ones will appear when it reasoned something wrong.
While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.
AI makes these projects significantly more feasible, at least in my domain. We have some critical-path software I wouldn't touch with such an approach, but the vast majority of our code is internal and/or supporting tooling.
For those cases, burning it down and rewriting via AI tooling has proven far more productive than anything we have attempted in the past. This is for old technical debt laden stuff everyone has been afraid to touch for well over a decade.
It's not perfect, but it moves the needle where before a lot of such projects were stuck on the backburner for years.
It certainly introduces new bugs and such, but at least this way forward momentum is happening vs. just being stuck in decision/analysis paralysis forever.
This also assumes some very senior SME folks are driving the process. I would not expect similar results with junior or even mid-level folks in these specific domains.
> While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.
One of the reasons to avoid rewriting has long been that the time spent rewriting code that works is time not spent writing code to meet new business needs. In other words, it's usually a huge opportunity cost, rarely balanced out by sufficient gains to be net positive.
I do think AI does challenge this prior, as the time needed to do a rewrite shrinks dramatically. It's not zero, of course, but it now becomes worth asking if it's worth doing, rather than defaulting to avoiding rewrites in nearly all cases.
We had to turn off a bunch of on-by-default features in the system I'm deploying now because IOS matches too aggressively and decides that arbitrary UDP datagrams are DHCP requests or PTP packets that need rewriting (and then dropping when they turn out to not be DHCP/PTP). I have to think that an AI rewrite with a today-good model would recognize the lax checks and do them better.
Is this like a PR piece for the guy? It's odd to see him singled out in a piece that would be normally be about the company, the CEO or the decision itself.
It does sound strange, like it was written by PR people. Tools are good but usually it is more subtle than asking one guy to rewrite everything. And of course any code written yesterday is legacy but it does not mean it should be rewritten.
We have an embedded system in one of product offerings that was largely developed using a bunch of “antiquated” technologies (over the past twenty years) and over the past year the two software devs that maintained it have retired. This normally would have big problem, but the entire codebase was re-written, documented, and modernized in a matter of about 3 months (for about $20k in tokens, and a mid level developer spending 50% of their time on it over that period). So it doesn’t surprise me to think a company like Cisco has piles of situations like this.
As much as I dislike AI, having worked on Cisco gear for years, I can't imagine AI can put out a worse product. If the re-write is full of bugs and security holes and static SSH keys, then it has not changed at all.
The problem with rewrites are that even if the rewrites are ultimately good it will tend to first create bugs on an existing thing that are presently churning in a stable state.
True. There were few (no other?) options for routers back then. I have fond memories of locking myself out of an ISP's core router then having to power cycle it.
It doesn't, but Cisco was great and they've just evolved into a laughing stock. Their stuff is really bad these days.
And they've overstretched their product line to too many things, trying to be the "be all" company. Fortinet is making the same mistake, but they're earlier in that process.
I mean, it's not really a mistake on their parts, their primary goal is to get rich and they are succeeding.
Citation: I've been working with Cisco technologies since the mid-1990s. At my current job, we are a few weeks away from phasing out the last of our Cisco junk. And since people will ask: to Juniper/Mist and Arista.
Or perhaps the lack thereof if you are one of the unsuccessful companies. In the 90s, I worked for a company that competed with Cisco I worked for a company that competed with Cisco. story was in the mid 80s an executive went to Silicon Valley. His report was that Cisco was a bunch of nobodies that would never go anywhere, which they'd go down the street and buy Vitalink instead. You have heard of Cisco and not Vitalink for a reason.
Back then they only really did routing and switching, and those are still the only things that Cisco kind-of does well.
Almost every new product of theirs I’ve touched in the last 20 years has been trash, and even the R&S golden goose is being dragged in that direction with customer-hostile functionality like Smart Licensing and a general decline in quality.
"Cisco Access Points That Are Running, Or Have Run, Releases 17.12.4, 17.12.5, 17.12.6, or 17.12.6a May Exhaust Flash Space, Preventing Upgrades"
Recovery path basically involves either factory resetting every single AP or up to, if it's already bricked, Cisco TAC + you having to console into every single bricked AP you have to pass a secret challenge/response at the bootloader to flash a recovery image :)
You don’t have very good imagination then. Cisco code is such a mess that there’s basically 0 chance he can even make a harness in 24 months, much less rewrite production code.
Indians have always been stereotyped for sycophancy and slavish adherance to spec over common sense, so it makes sense that that would go with being AI pilled.
I don't want to sound racist (which I'm not), but in my experience Indian software developers have often been less careful and concerned about quality than the average developer; it probably comes from many only becoming so for the job prospects, and not having much computer experience before college.
So it's not surprising if they embrace AI.
There's also that Indian cheaper outsourcing companies risk being displaced by AI, if they don't adopt it extensively to further reduce their pricing.
Does this one engineer have the domain knowledge to know WHY the old code was written the way it was, and what the graybeards would have done differently if they could start again now?
Otherwise he's just going to replicate all the legacy bugs and questionable design decisions.
Looks like his startup was some kind of translation service. So yeah he is totally qualified. It's a miracle how Jeetu Patel was able to find Padmanabhan Krishnamurthy or even know that he was under employed languishing somewhere in the bowels of CISCO. I wonder if they know each other from India?
His startup was acquired by Cisco so not weird for Cisco's CPO to know the startup's founder/CEO. That said, not sure how knowledge on speech translation means he's totally qualified on rewriting infra/networking/cybersecurity (Cisco's primary fields of operation) code. Unless the legacy code expected to be rewritten is constrained on related services/solutions, e.g. CVP or/and WebEx.
I've never heard of Ponytail before, I've read the entire README and glanced through this repo and I'm left so confused. From what I can gather this project is essentially a single markdown file with a prompt that verbosely says "write the simplest code". Yet the repo itself looks so bloated and complex and has so much activity. This feels like satire similar to fizzbuzz enterprise edition[1] but apparently this is the actual state of our industry?
Legacy code is typically a euphemism for old unmaintained code, no one knows how it works so it can be edited, and it probably doesn't align with current work practices.
Not to say a rewrite is necessary right, but avoiding rewrites of working code is how we ended up with more COBOL code than COBOL programmers in 2026.
I think this is actually the opposite in practice. LLMs generate better tests than they are at assessing which tests are effective (and, inferentially, how a system should behave). See: https://arxiv.org/abs/2410.21136
At my previous place, we had to write unit tests to cover each and every line of code. So if you add 10 lines of code, you ended up writing 100 lines of unit tests, mocking this service and that service, etc.
Once AI came along, I became like Captain Picard (RIP) and would just sit back and let the AI write all unit tests. "Try harder, make sure coverage is 100%". It was very exhilarating to sit back and watch the models churn away, creating 100s of lines of unit tests. Of course, I checked them all manually before submission ;-)
Documentation in "plain english", architecture diagrams, comments, and documentation are notorious for being unreliable, out-of-sync, and not as precise a specification as the code itself.
The issue with using "the code as the spec" is that humans can't read 100K lines of code in a day, can't hold the entire ball of unstructured mud in their brains all at once, and generally require hierarchical "structure".
Modern AIs just don't have these issues! Their context windows are big enough to encompass an entire codebase, so they can "see everything", all at once.
Each line of new code they write is compared against every relevant line of code in the original, which they treat as a spec.
My main issue in my experience is that that AIs tended to reproduce the legacy behaviour "bug for bug", which was not my intention.
Similarly, the AIs were hamstrung by external constraints: I typically prefer to leave the DB schema unchanged, which meant the torturous workarounds were needed for design errors in some stored procedures, etc.
The older the code, the bigger the issues with baked-in assumptions about transactions, stateful sessions, data types, string formats, etc.
This trips up AIs just as much as humans. You can't trivially maintain backwards compatibility and modernise the codebase! Those are conflicting goals, no matter what.
Most successful companies and innovative ideas come from middle aged founders and inventors. Silicon Valley loves the romantic notion of a contrarian young adult or even teenager "seeing what nobody else sees" , but they are the exception and not the rule.
Well they say the last 20% of the work takes 80% of the time so if he gets the prototype in 4 weeks, which I have no doubt he will be able to do, and assuming that prototype is the first 80% of work, then he should be able to do this in 20 weeks. He even has some margin! Looking forward to seeing the results
> “I’ve given him unlimited tokens because he’s going to refactor code,” Patel told Fortune at a small roundtable dinner. “So I’m like, you can go, you can go nuts.”
I think that Fortune story is better than the Tom's Hardware one. It ties the Cisco anecdote into a larger trend of some people deliberately hiring younger, less experienced developers for their AI projects - because they are more likely to be "AI native".
Sadly, I think the label "AI naïve" is better applied to the many experienced professionals who refuse to engage with AI systems as a matter of principle - or who tried out ChatGPT in 2024, saw it make howlingly obvious errors, and wrote off the entire category.
I frequently find myself in conversations with people who are resistant to AI and turn out to have a very skewed idea of what it can and cannot do.
I guess Cisco decided it has not alienated its customers enough till now & its finally time to get people running for the woods - at least if those peoples would like their network to continue working.
Given that a Cisco switch can be replaced with some other company's switch(at least in theory, idk), without weird unknown cases interfering, why would this be a problem ?
Not that straightforward. Similar to CPUs and other HW, there are errata and interop quirks between devices.
There are also tight time budgets (basically SLAs) that must be met along with memory considerations (both in SW and on the NPU/HBM), not to mention how the device needs to respond to load and various failure scenarios.
Manufacturers can’t even maintain OIDs between releases. I hope the AI will help. Ciena isn’t any better than Cisco, they broke their OIDS for the switches we use and we have to wait until mid 2027.
to be fair SNMP is just bad. Only redeeming feature of it is "takes little RAM to run it" (which was important when average networking device might've had only 2MB of RAM, not so in last 30 years).
The whole design where you need to get a magical list of IDs to decode the metrics and the list is not even shipped with device is entirely asinine
It's way more complicated than that. Bear in mind many of the network protocols in use today are decades old and have been constantly evolving, but there has generally been a consideration to maintain interoperability.
Then consider that not all vendors implement the standards identically, because the standards can be a bit woolly and in some cases followed rather than lead live implementations.
There will be a bunch of code that looks useless, but is actually there because of specific interoperability scenarios.
I'm probably not describing the scale of the issue adequately. Lots of these bugs only show up when you have a specific bit of hardware on a specific version of code, and it's connected to another specific bit of hardware running another specific version of code.
Lots of this stuff should work in theory, you only find out that it doesn't in practice when you try it on real hardware. And there are thousands of bits of hardware.
you assume their code is well written, while in reality the history of weird quirks and thousands upon thousands of CVE doesn't make the code underneath look well designed and written.
But yes, fact it uses a bunch of very well documented standards with multiple implementations gonna help massively
If i was an ex founder and having a low profile in a big company, I am doing it on purpose, either to have a peaceful life or heal from a burnout, definitely I don’t want to be on the spot like that, especially when I am not innovating anything new nor I will take any meaningful credit after since it will mostly go to AI, worse, if it didn’t work out I will have my career ruined being known to had an unlimited supply of tokens and still failed.
He'll pull it off, get feature complete, and spend a year or two with better models as they are released ironing it out. We just did an experiment, in four weeks generated 3500 commits, 200k sloc with a 1:1.15 ratio of production to test code and it all works very well. We are well on our way from 10x to 100x.
It is for internal use and so far so good. We are finding bugs and we just point the models at it with a strict red-first TDD approach and they've done very well fixing them. It certainly isn't perfect but the issues are very similar to what you get with a team of humans doing the same thing.
The main takeaway though is we had one person, in a single month, do the equivalent of at least a couple years of work for a small team. We view bugs and performance issues as a currently inevitable part of the process and we are dealing with them with models just like we do with humans on every other project already. Overall though it is representing an absolutely massive speedup. If you work in an environment where the models make egregiously more mistakes than your human counterparts then I am quite jealous.
ha ha .. that sounds like an Onion article. To be fair - if they did a narrow refactor to focus on fixing only obvious and known issues, they probably might be able to pull it off because a ton of that code is hairballs.
I mean, this is going to be easy. I've worked on Cisco gear before and this will be a simple job for AI. The big question is what the goal is... so you've rewritten new C++ code or ported to a newer version of Linux? Or you've unified the codebase of the Catalyst + Meraki switches?
Not clear to me what he's doing. Re-implement switching? Simplify features? Reduce LoC? Add test coverage? Either way, AI in that world will be helpful. I'm sure it'll spot all kinds of problems in opaque drivers that are hard to follow from MF specs.
So there's a real risk that Cisco might become history in just a few years. Taking that kind of risk with a rather unproven technology has to be psychosis. Or is that kind of belief a form of Religion?
I suspect we are approaching a world where this makes sense to do annually. Opus 5.5 is good enough to improve on most codebases, and Opus 7 will no doubt be good enough to improve on that.
'98% of the company's legacy code' is very vague. How many code bases? How each code base is connected to any supported Cisco product? How many KLOC the company's legacy code?
These are good questions that we won’t get answers to anytime soon.
I’d love to know what internal services and tools that are included in this, as well as any deliverables that shipped as software products to customers.
If it’s legacy code for IOS firmware, however, I’d be very worried.
Having to rewrite decades worth of legacy Cisco code is going to make Claude retire and start a goose farm.
Or trigger the built in protection against abusing Claude.
Anybody have an estimate of how much that is going to cost in token cost?
There's no goal mentioned in this article as why 98% of the code needs rewriting.
Yeah - code rewrites are generally a thing to be avoided since the requirements of older production code is typically not fully documented, even if it originally had been. Production code accumulates bug fixes, performance tweaks, special cases, additional requirements, etc, with documentation and test suites not always being updated in sync.
Your rewritten codebase will presumably look much cleaner and more maintainable that what it's aiming to replace, but it's easy to miss the purpose/necessity of all of the old "cruft" which need not be just poor coding but rather later enhancements not anticipated by the original design whose implementation was therefore crufty.
Does anyone here work at Cisco, and have any insight as to why a rewrite is considered necessary and might be expected to succeed?
A rewrite is a slam dunk for any decent frontier AI. It has a penchant for maintaining API/etc contracts to a fault in the absence of instructions to the contrary. It can easily validate its work and loves building exhaustive test cases. You can tell it to get 100% code coverage if you want. It will laborously accurate document every accumulated edge case and help you find a better overall cohesive structure.
A rewrite has historically been a huge mistake in many situations, some of which I've personally had the agony of witnessing firsthand, powerless to stop it. But AI completely changes the calculus because it doesn't waste significant developer time or energy crawling back to the previous working state, it just does it while you go get coffee. And this I've found to be a huge benefit, that I can continue making my codebases nicer to work with and better documented/integrated with bugs stamped out for free. There are upsides to a rewrite, and they're now much more likely to be worth it as the downsides are automated away.
The entire point of a rewrite is to get rid of the behaviour you don't want, while you keep the behaviour you do want. Consider the pathological case: Rewriting your FORTRAN codebase in Rust would obviously be useless if you had to reimplement every bug in the rewrite.
An LLM doesn't have enough context to know what you so and don't want. If you give it call logs for every function that was called and how, maybe, but a seasoned engineer will have more context around what the company needs.
Not necessarily, a rewrite can just move to a language that's easier to maintain (off C / cobol).
Honestly though, it's pretty clear the AI rewrites work, we have a ton of high profile examples. It's just a holdover attitude about rewrites from before AI. In reality, AI is going to make the code better when it rewrites
Defining the legacy bugs and porting them as features during the rewrite is actually one of the most difficult parts of enterprise rewrites.
You don't get to pick what parts of the API you're porting during something like that, it has to work the same or some of the ecosystem around it will break.
If this was true then Python would already have been rewritten to be GIL-free, and the entire ecosystem of Python packages would have been rewritten to respect its API.
In my experience it's been much simpler to rewrite programs from Python to <insert lower level language of choice here>
Absence of evidence is not evidence of absence! We're on this thread because Cisco is sponsoring piles of tokens at the problem. No such megacorp sponsor exists for this problem for Python. The megacorps have decided not to sponsor that specific problem.
I'd even argue AI is better for maintaining/moderninzing existing code than writing it, just because there is so much less input from developer about architecture it requires, as it has it in the code itself.
But there is pretty big risk of false positives and negatives; some "bugs" are design decisions that were not documented well/at all, and inevitably some new ones will appear when it reasoned something wrong.
While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.
AI makes these projects significantly more feasible, at least in my domain. We have some critical-path software I wouldn't touch with such an approach, but the vast majority of our code is internal and/or supporting tooling.
For those cases, burning it down and rewriting via AI tooling has proven far more productive than anything we have attempted in the past. This is for old technical debt laden stuff everyone has been afraid to touch for well over a decade.
It's not perfect, but it moves the needle where before a lot of such projects were stuck on the backburner for years.
It certainly introduces new bugs and such, but at least this way forward momentum is happening vs. just being stuck in decision/analysis paralysis forever.
This also assumes some very senior SME folks are driving the process. I would not expect similar results with junior or even mid-level folks in these specific domains.
Does the coding assistant demonstrate any tricks to improve the likelihood of success for such rewrites?
> While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.
One of the reasons to avoid rewriting has long been that the time spent rewriting code that works is time not spent writing code to meet new business needs. In other words, it's usually a huge opportunity cost, rarely balanced out by sufficient gains to be net positive.
I do think AI does challenge this prior, as the time needed to do a rewrite shrinks dramatically. It's not zero, of course, but it now becomes worth asking if it's worth doing, rather than defaulting to avoiding rewrites in nearly all cases.
AI has electrolytes!
The hardware it runs on has capacitors as its components and some of them do in fact contain electrolytes.
It’s what the shareholders crave!
They also seem to crave everything that has the word AI in it.
These are references to an excellent, hilarious, and sadly more relevant than ever, movie:
Idiocracy (2006): https://en.wikipedia.org/wiki/Idiocracy
Movie? I prefer to think of it as a documentary made in advance.
Somebody needs a promo packet. Duh
Because it's Cisco?
We had to turn off a bunch of on-by-default features in the system I'm deploying now because IOS matches too aggressively and decides that arbitrary UDP datagrams are DHCP requests or PTP packets that need rewriting (and then dropping when they turn out to not be DHCP/PTP). I have to think that an AI rewrite with a today-good model would recognize the lax checks and do them better.
It's got tabs instead of spaces. Yuck!
It's what Cisco does, as they've done several times before.
It is not in Rust.
No goal, and no results, but a younger guy was enthused about AI!
It's because the old bits are starting to stink a bit from age. Get those stinky bits out of here, I say! Let the AI make some new bits!
Is this like a PR piece for the guy? It's odd to see him singled out in a piece that would be normally be about the company, the CEO or the decision itself.
It does sound strange, like it was written by PR people. Tools are good but usually it is more subtle than asking one guy to rewrite everything. And of course any code written yesterday is legacy but it does not mean it should be rewritten.
Seems like preparing who to blame if/once the effort fails. ;-)
We have an embedded system in one of product offerings that was largely developed using a bunch of “antiquated” technologies (over the past twenty years) and over the past year the two software devs that maintained it have retired. This normally would have big problem, but the entire codebase was re-written, documented, and modernized in a matter of about 3 months (for about $20k in tokens, and a mid level developer spending 50% of their time on it over that period). So it doesn’t surprise me to think a company like Cisco has piles of situations like this.
That's really interesting.
What have been achieved using this port?
And how did you make sure the port is correct?
As much as I dislike AI, having worked on Cisco gear for years, I can't imagine AI can put out a worse product. If the re-write is full of bugs and security holes and static SSH keys, then it has not changed at all.
The problem with rewrites are that even if the rewrites are ultimately good it will tend to first create bugs on an existing thing that are presently churning in a stable state.
It's sad to hear how Cisco has fallen. I remember working on some early ISP networks in the 90's. Cisco was everywhere!
Just because something is/was widely deployed does not mean it was good
True. There were few (no other?) options for routers back then. I have fond memories of locking myself out of an ISP's core router then having to power cycle it.
I remember routers being Very Expensive and so realizing you could route 10mb/s with an old Pc and some 3com cards and BSD was a big deal.
It doesn't, but Cisco was great and they've just evolved into a laughing stock. Their stuff is really bad these days.
And they've overstretched their product line to too many things, trying to be the "be all" company. Fortinet is making the same mistake, but they're earlier in that process.
I mean, it's not really a mistake on their parts, their primary goal is to get rich and they are succeeding.
Citation: I've been working with Cisco technologies since the mid-1990s. At my current job, we are a few weeks away from phasing out the last of our Cisco junk. And since people will ask: to Juniper/Mist and Arista.
I was curious but wasn't going to ask, so thank you for adding it!
So was Oracle and Microsoft Windows.
If history has taught us anything. It’s that the measure of a successful product is usually more to do with its sales people.
Or perhaps the lack thereof if you are one of the unsuccessful companies. In the 90s, I worked for a company that competed with Cisco I worked for a company that competed with Cisco. story was in the mid 80s an executive went to Silicon Valley. His report was that Cisco was a bunch of nobodies that would never go anywhere, which they'd go down the street and buy Vitalink instead. You have heard of Cisco and not Vitalink for a reason.
Back then they only really did routing and switching, and those are still the only things that Cisco kind-of does well.
Almost every new product of theirs I’ve touched in the last 20 years has been trash, and even the R&S golden goose is being dragged in that direction with customer-hostile functionality like Smart Licensing and a general decline in quality.
They didn't even need the AI to make thousands of hot bricks nationwide. Here's just one of the latest hits...
https://www.cisco.com/c/en/us/support/docs/field-notices/743...
"Cisco Access Points That Are Running, Or Have Run, Releases 17.12.4, 17.12.5, 17.12.6, or 17.12.6a May Exhaust Flash Space, Preventing Upgrades"
Recovery path basically involves either factory resetting every single AP or up to, if it's already bricked, Cisco TAC + you having to console into every single bricked AP you have to pass a secret challenge/response at the bootloader to flash a recovery image :)
You don’t have very good imagination then. Cisco code is such a mess that there’s basically 0 chance he can even make a harness in 24 months, much less rewrite production code.
There also seems to be some weird hero-worship from the CEO, directed at this 27-YO engineer? Like, "he is the one who can save us."
Both Indians, and Indians on average seem to have gone more heavily on careless AI than the worst American psychotics
Indians have always been stereotyped for sycophancy and slavish adherance to spec over common sense, so it makes sense that that would go with being AI pilled.
I don't want to sound racist (which I'm not), but in my experience Indian software developers have often been less careful and concerned about quality than the average developer; it probably comes from many only becoming so for the job prospects, and not having much computer experience before college.
So it's not surprising if they embrace AI.
There's also that Indian cheaper outsourcing companies risk being displaced by AI, if they don't adopt it extensively to further reduce their pricing.
It's also a bit of a teached culture to "ship fast" there, it's all about "making the sale", quality often comes only afterward.
Maybe his blood boy's high on gourmet cannabis and Oreos.
https://www.youtube.com/watch?v=hBA0AH-LSbo
I chose to interpret it as "our codebase is that bad we need a hero"
Unless they also have 750K tests like sqlite do, I can't imagine this will go well, even if/especially if the legacy code warrants a refactor.
Better than 750k tests is millions of customers! They’ll test it for you!
Does this one engineer have the domain knowledge to know WHY the old code was written the way it was, and what the graybeards would have done differently if they could start again now?
Otherwise he's just going to replicate all the legacy bugs and questionable design decisions.
I have no doubts that there will also be new bugs.
the premise does sound a lot like written by someone who is looking for hype and not sounding credible
Looks like his startup was some kind of translation service. So yeah he is totally qualified. It's a miracle how Jeetu Patel was able to find Padmanabhan Krishnamurthy or even know that he was under employed languishing somewhere in the bowels of CISCO. I wonder if they know each other from India?
The entire story sounds very weird.
They met each other by chance and began work rewriting the entire company's codebase over a firm handshake
You forgot to mention the translation company he helped found was also acquired by this same CEO. :))
His startup was acquired by Cisco so not weird for Cisco's CPO to know the startup's founder/CEO. That said, not sure how knowledge on speech translation means he's totally qualified on rewriting infra/networking/cybersecurity (Cisco's primary fields of operation) code. Unless the legacy code expected to be rewritten is constrained on related services/solutions, e.g. CVP or/and WebEx.
His job isn’t to rewrite all the code. His job is to make the market satisfied that Cisco is “more AI” than competitors.
He doesnt need that when he has Ponytail https://github.com/DietrichGebert/ponytail
Right? ...
I've never heard of Ponytail before, I've read the entire README and glanced through this repo and I'm left so confused. From what I can gather this project is essentially a single markdown file with a prompt that verbosely says "write the simplest code". Yet the repo itself looks so bloated and complex and has so much activity. This feels like satire similar to fizzbuzz enterprise edition[1] but apparently this is the actual state of our industry?
[1] https://github.com/enterprisequalitycoding/fizzbuzzenterpris...
The date picker example is perhaps the best worst they could have picked.
Anyone who has used the built in date picker knows why everyone rolls their own.
Literally anyone can do this
Rewrite it in service of… what exactly?
It says "legacy" code.
Legacy code is typically a euphemism for old unmaintained code, no one knows how it works so it can be edited, and it probably doesn't align with current work practices.
Not to say a rewrite is necessary right, but avoiding rewrites of working code is how we ended up with more COBOL code than COBOL programmers in 2026.
If nobody knows how the old code works, how will anyone know how the new code (written by an autonomous agent) works?
Regression tests?
I think people are assuming the worst but AIs most helpful contribution beyond churning out code is explaining the code base.
Who knows if they will do a good or bad job that's down to the engineers and not the tools imo.
Why is that better than having the agent(s) write regression tests or explanations of the old codebase?
I think this is actually the opposite in practice. LLMs generate better tests than they are at assessing which tests are effective (and, inferentially, how a system should behave). See: https://arxiv.org/abs/2410.21136
That said, there's also research pointing to LLMs encoding existing bugs as test requirements: https://arxiv.org/abs/2607.05139
That CS PHD researcher, Konstantinou, in particular, has written a lot on this: https://arxiv.org/search/cs?searchtype=author&query=Konstant...
At my previous place, we had to write unit tests to cover each and every line of code. So if you add 10 lines of code, you ended up writing 100 lines of unit tests, mocking this service and that service, etc.
Once AI came along, I became like Captain Picard (RIP) and would just sit back and let the AI write all unit tests. "Try harder, make sure coverage is 100%". It was very exhilarating to sit back and watch the models churn away, creating 100s of lines of unit tests. Of course, I checked them all manually before submission ;-)
Documentation in "plain english", architecture diagrams, comments, and documentation are notorious for being unreliable, out-of-sync, and not as precise a specification as the code itself.
The issue with using "the code as the spec" is that humans can't read 100K lines of code in a day, can't hold the entire ball of unstructured mud in their brains all at once, and generally require hierarchical "structure".
Modern AIs just don't have these issues! Their context windows are big enough to encompass an entire codebase, so they can "see everything", all at once.
Each line of new code they write is compared against every relevant line of code in the original, which they treat as a spec.
My main issue in my experience is that that AIs tended to reproduce the legacy behaviour "bug for bug", which was not my intention.
Similarly, the AIs were hamstrung by external constraints: I typically prefer to leave the DB schema unchanged, which meant the torturous workarounds were needed for design errors in some stored procedures, etc.
The older the code, the bigger the issues with baked-in assumptions about transactions, stateful sessions, data types, string formats, etc.
This trips up AIs just as much as humans. You can't trivially maintain backwards compatibility and modernise the codebase! Those are conflicting goals, no matter what.
I don't think no one knows how it works. I just think the people using the word "legacy" for it are boneheaded.
Most successful companies and innovative ideas come from middle aged founders and inventors. Silicon Valley loves the romantic notion of a contrarian young adult or even teenager "seeing what nobody else sees" , but they are the exception and not the rule.
Well they say the last 20% of the work takes 80% of the time so if he gets the prototype in 4 weeks, which I have no doubt he will be able to do, and assuming that prototype is the first 80% of work, then he should be able to do this in 20 weeks. He even has some margin! Looking forward to seeing the results
Misleading title, someone should fix it. 98% of legacy code. Check out the full title of the article.
Does Cisco have non-legacy code?
My favorite description of JAVA is that it's a language where you are deploying instant legacy code.
"Java is a DSL for taking large XML files and converting them to stack traces." -Andrew Back
https://www.reddit.com/r/programming/comments/eaqgk/java_is_...
"XML is like violence: if it doesn't solve your problem, you aren't using enough of it." -Chris Maden
https://www.reddit.com/r/ProgrammerHumor/comments/1mbgih/xml...
"XML is a giant step in no direction at all" -Erik Naggum
https://quotefancy.com/quote/1643080/Erik-Naggum-XML-is-a-gi...
"According to a report by Fortune" - here's that report: https://fortune.com/2026/10/30/cisco-president-jeetu-patel-g...
Fortune's source was the CEO himself:
> “I’ve given him unlimited tokens because he’s going to refactor code,” Patel told Fortune at a small roundtable dinner. “So I’m like, you can go, you can go nuts.”
I think that Fortune story is better than the Tom's Hardware one. It ties the Cisco anecdote into a larger trend of some people deliberately hiring younger, less experienced developers for their AI projects - because they are more likely to be "AI native".
more like AI naive
Sadly, I think the label "AI naïve" is better applied to the many experienced professionals who refuse to engage with AI systems as a matter of principle - or who tried out ChatGPT in 2024, saw it make howlingly obvious errors, and wrote off the entire category.
I frequently find myself in conversations with people who are resistant to AI and turn out to have a very skewed idea of what it can and cannot do.
Not the CEO. He’s the product officer.
I guess Cisco decided it has not alienated its customers enough till now & its finally time to get people running for the woods - at least if those peoples would like their network to continue working.
If only internet users could run for the woods
What's so special about the other 2%, is it good?
I think Cisco is an interesting use case for AI, because it's code, probably:
-Works according to a defined specification
-Within the bounds of that specification, has a lot of code written to optimize speed, cost, latency, etc - all measureable goals
-Written in c, with all it's weakness
-Given limitless engineering work, some could be ported to better hardware
-the new system could be automatically compared to the old system for functional correctness
All those factors fit well with agent based development.
Btw, many of them are true in general to embedded systems.
The first and last bullets are extremely optimistic. How do you possibly simulate all the weird interdependent behavior in real world networks?
Given that a Cisco switch can be replaced with some other company's switch(at least in theory, idk), without weird unknown cases interfering, why would this be a problem ?
Not that straightforward. Similar to CPUs and other HW, there are errata and interop quirks between devices.
There are also tight time budgets (basically SLAs) that must be met along with memory considerations (both in SW and on the NPU/HBM), not to mention how the device needs to respond to load and various failure scenarios.
there is software to simulate any arbitrarily complex network: GNS3, eve-ng, Cisco Modeling labs, etc
I'm talking about heterogenous legacy hardware that isn't owned by Cisco, not complex topologies.
Manufacturers can’t even maintain OIDs between releases. I hope the AI will help. Ciena isn’t any better than Cisco, they broke their OIDS for the switches we use and we have to wait until mid 2027.
to be fair SNMP is just bad. Only redeeming feature of it is "takes little RAM to run it" (which was important when average networking device might've had only 2MB of RAM, not so in last 30 years).
The whole design where you need to get a magical list of IDs to decode the metrics and the list is not even shipped with device is entirely asinine
It's way more complicated than that. Bear in mind many of the network protocols in use today are decades old and have been constantly evolving, but there has generally been a consideration to maintain interoperability.
Then consider that not all vendors implement the standards identically, because the standards can be a bit woolly and in some cases followed rather than lead live implementations.
There will be a bunch of code that looks useless, but is actually there because of specific interoperability scenarios.
That's a good point.
I wonder whether AI is any good at looking at that code,running the system, and documenting those edge cases?
I'm probably not describing the scale of the issue adequately. Lots of these bugs only show up when you have a specific bit of hardware on a specific version of code, and it's connected to another specific bit of hardware running another specific version of code.
Lots of this stuff should work in theory, you only find out that it doesn't in practice when you try it on real hardware. And there are thousands of bits of hardware.
I worked at Cisco on one of the IOS-XR teams. It’s way more complex than you think it is.
This whole thing sounds like a deluded vanity project birthed in an ivory tower.
That describes everything Jeetu is involved in. I'm very glad to have recently left Cisco.
you assume their code is well written, while in reality the history of weird quirks and thousands upon thousands of CVE doesn't make the code underneath look well designed and written.
But yes, fact it uses a bunch of very well documented standards with multiple implementations gonna help massively
If i was an ex founder and having a low profile in a big company, I am doing it on purpose, either to have a peaceful life or heal from a burnout, definitely I don’t want to be on the spot like that, especially when I am not innovating anything new nor I will take any meaningful credit after since it will mostly go to AI, worse, if it didn’t work out I will have my career ruined being known to had an unlimited supply of tokens and still failed.
Cisco that powers more than half of the backbone of all things online? Are we trying to lose control of AGI as soon as it emerges??
When this rewrite breaks the internet AGI won't be able to take over. It's very forward-thinking.
They need to cut cost & to figure out productivity per engineer. They're doing this b/c they are going to significantly cut their engineer workforce.
He'll pull it off, get feature complete, and spend a year or two with better models as they are released ironing it out. We just did an experiment, in four weeks generated 3500 commits, 200k sloc with a 1:1.15 ratio of production to test code and it all works very well. We are well on our way from 10x to 100x.
Did you check with the end user as to how well its actually working? My prior company is doing this and their platform has gone to latency/bug hell.
It is for internal use and so far so good. We are finding bugs and we just point the models at it with a strict red-first TDD approach and they've done very well fixing them. It certainly isn't perfect but the issues are very similar to what you get with a team of humans doing the same thing.
The main takeaway though is we had one person, in a single month, do the equivalent of at least a couple years of work for a small team. We view bugs and performance issues as a currently inevitable part of the process and we are dealing with them with models just like we do with humans on every other project already. Overall though it is representing an absolutely massive speedup. If you work in an environment where the models make egregiously more mistakes than your human counterparts then I am quite jealous.
and if you enable dangerously_skip_permissions you can probably even get to 1000x
ha ha .. that sounds like an Onion article. To be fair - if they did a narrow refactor to focus on fixing only obvious and known issues, they probably might be able to pull it off because a ton of that code is hairballs.
its never unlimited....
Shocking to realize how many on HN do not realize that this is NOT a tall order, and has not been a feat for at least six months.
Shocking how many on HN do not realize how devastating this can be
I mean, this is going to be easy. I've worked on Cisco gear before and this will be a simple job for AI. The big question is what the goal is... so you've rewritten new C++ code or ported to a newer version of Linux? Or you've unified the codebase of the Catalyst + Meraki switches?
Not clear to me what he's doing. Re-implement switching? Simplify features? Reduce LoC? Add test coverage? Either way, AI in that world will be helpful. I'm sure it'll spot all kinds of problems in opaque drivers that are hard to follow from MF specs.
The goal is to use AI, full stop
Cisco is losing to competitors in some features/products, for example to juniper mist.
rewrite can be done to quickly refactor and/or close the feature parity, improve the UI/UX for end customer, add missing features or integration needs
Maybe Stanford found some more of their stolen code being used by Cisco. /s Cisco origins is a fascinating subject.
So there's a real risk that Cisco might become history in just a few years. Taking that kind of risk with a rather unproven technology has to be psychosis. Or is that kind of belief a form of Religion?
Clear case of AI psychosis.
Many customers will definitely stick with the pre-sloppified versions of IOS.
Source: https://fortune.com/2026/10/30/cisco-president-jeetu-patel-g... (https://news.ycombinator.com/item?id=50303001)
rewriting code is the easy part
it's the testing in real world usage to shake out all the edge cases and bugs that's hard and that you can't just write unit tests for
I suspect we are approaching a world where this makes sense to do annually. Opus 5.5 is good enough to improve on most codebases, and Opus 7 will no doubt be good enough to improve on that.
'98% of the company's legacy code' is very vague. How many code bases? How each code base is connected to any supported Cisco product? How many KLOC the company's legacy code?
These are good questions that we won’t get answers to anytime soon.
I’d love to know what internal services and tools that are included in this, as well as any deliverables that shipped as software products to customers.
If it’s legacy code for IOS firmware, however, I’d be very worried.