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Comment by zzyzxd | Hacker News Reader

I have a GL.iNet travel router. When I am not travel, it connects to the router's second WAN port. If my main internet goes down, it takes me 30 seconds to tether my phone and failover manually. My carrier detects and throttles hotspot traffic by measuring packets TTL, so I tweaks the router's iptables to dodge that. Typically I get over 400 Mbps.

From time to time I get the itch to improve my home network uptime, and I have to keep reminding myself that the current setup is fine.

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(Tangential, regarding GL.Net routers: I find it satisfying that these routers run OpenWRT out of the box, and top the "Travel routers" category on Amazon: "Overall Pick" and "Amazon's Choice".)

I run several GL.Net routers in a mesh across two continents, some have Starlink and cellular, some on regular ol' fiber. They are bulletproof, highly recommend.

How do you do that in a mesh?

Headscale

https://github.com/juanfont/headscale

A VPN?

A wireguard tunnel from every router to every other router. Software defined network stack.

It's probably because usually normal people don't but routers because they get them included in their internet subscription. So the people buying them have a specific reason to that normal routers don't do

It's a travel router which power users buy to get good connectivity away from home and office. An hotel won't offer you that (and chances are that they'll try to rip you off on their wifi).

Assuming you can find an Ethernet port to supply it, that is. Most hotels don't make them easy to find and use, if they even have them.

More common is that you use the travel router to connect to hotel WiFi and then share out that connection. It's slower than using directly, but it's great for family travel since you can name your travel SSID the same as your home network - all your usual devices will connect automatically, and will use any whole-connection VPN you have set up (most of the gl.inets will do Wireguard, OpenVPN, and Tailscale that I know of straight out of the box, and they will let you into luci or via SSH to configure the underlying OpenWRT directly for anything else). And, of course, it's just one device for hotels that try to limit the number of devices you use.

As far as travel and hotel goes, another huge benefit is that the router enables devices without captive portal support, on a recent trip I can use: - Fi base station for my dogs trackers (huge for me) - FireTV stick (no need to trust hotel streaming apps will clear your credentials like they claim)

Also I can WireGuard back home automatically for select IP ranges (no need to configure WireGuard separately on many of my devices)

> My carrier detects and throttles hotspot traffic by measuring packets TTL, so I tweaks the router's iptables to dodge that.

Could you elaborate on this?

I have a friend that is also curious. Their fibre cable was cut by addicts trying to find a source of copper that took a few days to be repaired. Using their hot spot during the outage used up their allotted hot spot bandwidth for the month. My friend would be very interested in how to avoid potential down time in the future.

Might I suggest an email address added to your HN profile, lest a publicly posted reply result in observation by a nefarious telecom employee who just might obviate the proposed solution to your friend’s conundrum.

Are we back to this again? I have a friend who wants to know how to build a blue box.

One step from ‘SWIM tried meth and he’s freaking out’ from the old forums !

TTL++l0l

Sure, it's widely known.

Default TTL is usually 64.

Phone traffic TTL is 64.

But when behind the phone-as-router/gateway, compy traffic TTL is...63!

Thanks!

Some mobile phone providers check the packet TTL to limit tethering.

Network packets commonly have start with default TTL values of 64, 128, or 255. Each hop in the network subtracts 1.

When phone connects direct to carrier (cell tower, I assume) the carrier will see TTL of 64.

A laptop tethered to a phone introduces a hop so laptop-to-phone TTL is 64, phone-to-carrier TTL is 63.

Carriers can then limit bandwidth if network packet that don't have a common TTL.

For `iptables` look at `--ttl-inc 1` (to add back the 1 so 63 => 64) or `--ttl-set 64`.

Alternatively, you set the tethered devices to use a TTL of 65, e.g. linux/mac `sysctl -w net.inet.ip.ttl=65`

How do you figure out what detection method a carrier is using?

Make the TTL change , and see if traffic bw changes?

Thank you for explaining this, I had always wondered how a carrier could tell a device was tethered if a router was not passing on tethered device details.

If the hotspot is sourced from the phone, the phone tells the carrier

Another way to do it is to look for requests to domains that phones never access but desktops/laptops often do. Windows Update is the most common, but you could probably do apt package repositories or whatever.

Thanks!

You can easily manipulate and set TTL to whatever is needed with a Mikrotik router. Override TTL for all devices behind it.

/ip firewall mangle add chain=postrouting out-interface=lte1 action=change-ttl new-ttl=set:64 passthrough=yes comment="Set TTL for Mobile Hotspot"

I have AT&T Fiber and 99% of the time it's fantastic, but there are several instances of 30-60 second downtime a day and I have a 5G modem with a Google Fi data sim as a backup. Failover is nearly-instant with a Unifi UDM.

The data sim costs nothing extra on top of my cellular plan and just counts towards my (already very generous) monthly limit of 50GB.

Out of curiosity what carrier are you using?

Pulled the thread on this a bit and it seems that it will be highly carrier-dependent and will likely be flakey if it works at all.

TTL is one of the simplest methods carriers use to detect if there's an extra hop but very unlikely to be their only line of defense against methods like this.

Is your phone connected to the router through a cable or wirelessly?

They can do both - cable or bluetooth. Don't think wifi

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