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Comment by xgbi | Hacker News Reader

Launch ´mtr google.com’ on one of your devices (preferably connected via Ethernet to your router) a few minutes before the cut off, and watch what happens when the cut occurs. It will show you exactly which equipment on the route starts dropping.

Although I suspect your ISP has a 24h lease and your modem renegociates at 3:40 everyday

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Here's a summary from the man pages of mtr, for those who are not familiar with the tool but maybe are reading HN on their phones so can't check it out:

    mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
    
    As mtr starts, it investigates the network connection between the host mtr runs on and HOSTNAME by sending packets with purposely low TTLs. It continues to send packets with low TTL, noting the response time of the intervening routers. This allows mtr to print the response percentage and response times of the internet route to HOSTNAME. A sudden increase in packet loss or response time is often an indication of a bad (or simply overloaded) link.
    
    The results are usually reported as round-trip-response times in milliseconds and the percentage of packetloss.

This actually makes me wonder about whether there's a command that'll let me see short summaries of what every file under /usr/bin is, in the form of a list. Definitely wasn't aware of mtr as an average web developer up until now.

apropos -s 1 . will list a short description from the manpages (might have to run mandb first)

Actually it seems that it is not renegotiating everyday: it is expiring and re-requesting.

The way DHCP 'should' work is that when a client is part-way through the lease it should try to renew the IP it already has:

* https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Pro...

* https://tools.ietf.org/html/rfc2131#section-4.4.5

This allows the client to (hopefully) keep extending the IP it has so that a re-IP does not cause current connections to drop. If the modem is not doing this (can the OP log into it in someway to see logs?), then it is acting as a 'non-ideal' DHCP client.

Until this is sorted out, try rebooting the modem an an 'odd' hour that will not disrupt you during the day. This is no guarantee though: the DHCP server may remember the old/current DHCP lease and simply re-issue it with the same expiration time.

I'm on DSL/PPPoE, so this may not apply, but: my Asus router has a setting that allows it to automatically reboot. I do this at ~04h00 to get a new IP every day so help with privacy concerns. I generally surf with cookies disabled, so these two things help with the low-hanging fruit of simple tracking techniques. (My DSL modem is bridged.)

I had this exact issue in 2008 in SF on Comcast Business.

The lease would be dropped and renegotiated every few hours, we could notice it because our SSH tunnels would get torn down.

What was annoying was that the business plan had a static IP associated with it, presumably managed by their DHCP setup.

It took weeks to convince Comcast the issue wasn’t in our building, and moments for them to fix once they “got it”.

What piece of evidence or logs finally convinced Comcast that the issue was on their side?

Honestly my memory is not that good! I remember a few tech visits as they replaced modems, etc, and I eventually got to some “3rd level support person” that said something akin to “oh, that issue again”.

Did you try saying shibboleet?

https://xkcd.com/806/

c.f. Judges 12:5-6 (https://www.bible.com/bible/114/JDG.12.5-6.NKJV):

> The Gileadites seized the fords of the Jordan before the Ephraimites arrived. And when any Ephraimite who escaped said, “Let me cross over,” the men of Gilead would say to him, “Are you an Ephraimite?” If he said, “No,” then they would say to him, “Then say, ‘Shibboleth’!” And he would say, “Sibboleth,” for he could not pronounce it right. Then they would take him and kill him at the fords of the Jordan. There fell at that time forty-two thousand Ephraimites.

Haha - This is and the comment above are awesome. But not really a backdoor.

I saw this daily drop on several small biz Comcast setups. I recall I found it while looking through all the settings on the router, though I do recall having to call Comcast and they set something so it never happened again. It was the Comcast device with built in wifi. Hardwired didn't glitch, just wifi.

I could be wrong but this sounds more like NAT port issue given the frequency and static lease agreement on IP.

So then the trick is to forgo internet by disconnecting power from a few minutes before that time to the middle of the night and get power back? I do feel for the ISP's with this setup because the right thing to do would be to write in the installation manual: "Only install in the deep of night".

Well they could 1) renew the IP before it expires or 2) reboot the modem remotely at 3:30am for example.

Or assign a lease that expires at 0330 instead of a lease that expires in 24 hours.

But I’ve not experienced similar in 20 years of dynamic ips.

it depends. depending on the dhcp implementation on the server side you may have the same problem (ie while you get a new lease it may expire at the same time). unlikely but I’ve seen some stuff when it comes to dhcp

On the subject of Lease Time.

My router is currently showing a lease time of 3 Min. I think most router tends to renew their IP at 50% of ISP's lease time ( in this case 6 min )

What are the purpose of these ridiculously low lease time? I remember in the old days they tend to go for 48 hours if not longer.

To get you to pay more money for a static IP.

Seems Reasonable, but I though most ISP dont want Home users to be using Static IPs.

And apology for asking an off topic question. I guess that is what the downvotes are coming from.

There's a limited number of IPs so most homes CANT use static... we already don't have enough IPs for the mountains of devices.

But the other part is money... why give something away for free when you can make it a "feature" to pay for?

Tons of other reasons in various articles...

https://www.online-tech-tips.com/computer-tips/ott-explains-...

https://superuser.com/questions/590391/why-do-isps-change-yo...

I work at an ISP and setup both static and dhcp services. Statics take far more work and management than dhcp, ignoring the scarcity problem. We make you pay more because you are requesting something that requires both documentation and management on a home connection.

Id be glad to give them away for free but it is all downside for us and over 99% of residential customers dont want one to start with.

I think we have 3 residential customers out of 1500 that have statics.

After having read some of the articles on it (including the two listed), the mechanics are something that are probably a lot more intensive to manage than I figured initially. Changing DHCP is a couple changes and then... wait. Changing hard coded paths and all that...

I'm actually glad I don't deal with that stuff on a day to day... but I like learning about it.

un-ignoring the scarcity problem, when I've gotten a static IP I would usually get a block of 8 and they would waste the 0 for network and 7 for broadcast. I've wondered why they didn't just give you 8 usable addresses.

(or if I set up my own router could I just use the all?)

Most ISPs are using carrier grade NAT (CGNAT), so most users are sharing IPs with other customers.

Is there a citation for the "most" here? I understand this is true in some cases, but I've never used an ISP that does carrier grade NAT. I'm on Spectrum cable now, which is not exactly known for being a good ISP, and I have my own address.

This is the correct answer. Although typically leases will attempt a renewal halfway through the lease time, so it would be a 48 hour lease.

As OP said, mtr will tell you where in the line it’s happening.

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