Question

Hello all, hoping someone can help.

I've got a RUT240 but had to factory reset it as couldn't remember the password! (D'oh!) Everything is back up and running but some of the device that are connected are having trouble reaching certain websites, seems to be a DNS issue but other computers are absolutely fine. I dont use the wifi of the 240 as I have a Ubiquity AP that is fed from the 240 that covers the whole house, but DHCP is controlled from the RUT240. Any ideas of things to check please?

Answer 1

Do you have a linux or windows box in your network? Then try e.g.
    nslookup dns.google
from a shell / command line and see if you get 8.8.8.8 and 8.8.4.4
as an answer.

- then try asking google directly like so:
    nslookup dns.google 8.8.8.8
or ask cloudflare with
    nslookup dns.google 1.1.1.1
- then try asking your router
    nslookup dns.google 192.168.1.1
(assuming your router's IP is 192.168.1.1)

- then try setting your device to a static IP
    and its primary DNS manually to 8.8.8.8
- afterwards do various test with either ping
    or with your browser

If your results aren't conclusive then post
them here (anonymized if neccessary) and
I'll have a look at them.

I'm a firewall and router programmer btw. so
maybe I can be of some help.

Regards,

Reinhard

Comments

Hi Reinhard,

Thanks for your reply and many thanks for you help.

We are all on Mac but in terminal I get the following results, which I think means the DNS is correct?

I tried setting the address to static with DNS of 8.8.8.8 but no difference the same websites still wont load, yet if I change the house wifi to tethering from my phone, then the website loads immediately.

Just FYI, my phone and the home wifi are both on Vodafone (our broadband at home is totally useless becasue of our location so we binned it and just use a Teltonika 4G router to supply the home wifi through a Ubiquiti AP. Other devices connecting to the same AP and the same website, load perfectly.

Any thing else I can try?

Here is the terminal results:

Last login: Sun Jul 31 17:20:50 on console

charlotteballard@Charlottes-Air ~ % nslookup dns.google

Server: 192.168.1.1

Address: 192.168.1.1#53

Non-authoritative answer:

Name: dns.google

Address: 8.8.4.4

Name: dns.google

Address: 8.8.8.8

charlotteballard@Charlottes-Air ~ % nslookup dns.google 8.8.8.8

Server: 8.8.8.8

Address: 8.8.8.8#53

Non-authoritative answer:

Name: dns.google

Address: 8.8.4.4

Name: dns.google

Address: 8.8.8.8

charlotteballard@Charlottes-Air ~ % nslookup dns.google 192.168.1.1

Server: 192.168.1.1

Address: 192.168.1.1#53

Non-authoritative answer:

Name: dns.google

Address: 8.8.8.8

Name: dns.google

Address: 8.8.4.4

---

Ok, next step:
which devices do have trouble connecting?
Just mobile phones? Or just tablets?
Or does the problem occur on different
devices without a noticeable pattern?

I've had problems with the MTU being at max
and could solve them by reducing it to 1495
or even 1490. But that's just a shot in the dark.

Another question: do you have at least the
firmware RUT2_R_00.07.03.4 ?

Regards,

Reinhard

---

Hi Reinhard,

OK I was on old firmware but I've updated and now on 00_07_04.1 but still no change.

My MTU was set to 1470 but I ran some more test and it seemed liek anything more than 1440 and it stopped working so I've set it back to 1440 (had been on 1470 for the past year without a problem)

Sadly still no joy. Seems to be affecting all devices now but only to certain websites. Most main ones are OK but one in particular that we are trying to get to is bad through this connection but still if I jump to my mobile, tethered then it comes up straight away

---

Hi,

that's getting interesting...

Two more ideas to try:
- try setting the MTU to max (which is 1500), because it might be a problem with packet fragmentation
- try telnetting the affected webservers from the Mac's terminal, e.g.:
  telnet www.google.com 80
after successful connection type
  GET /
there you will get "interesting" things, mostly JavaScript, but at least you should get some data

---

Hi Reinhard.

I've been testing the MTu and it seems like whatever I set it to, when I then do Ping tests like this: 

ping 1.1.1.1 -D -s 1430

then the end result at roughly 30 less than what I've set the MTU at. ie if I set it to 1500, then anything above 1480 on the ping test fails, If I set it to 1430 then anything above 1400 in the ping test fails.

So currently its set to 1470, which to be fair is what I had it set at previously.

When I try to run a telnet command I get an error that says command not found. Just as a reminder I'm doing this on a Mac not a PC. I did try on my Parallels Windows 11 virtual machine but I got " 'telnet' is not recognized as an internal or external command,

operable program or batch file."

Any pointers to what I'm doing wrong.

The same website is still unreachable! - https://www.lambertshealthcare.co.uk/

But if I use my tethered it's straight in!

---

Hi,

just to make sure I get that right:
- you set the MTU of device mob1s1a1 on the RUT240 to e.g. 1470
  (yep, that was your original setting!)
- then you can ping with packets up to 1440 or so
- ping -D -s <packetsize> is the correct syntax on the Mac

Funny that telnet can't be found in the terminal, can't test
that right now, being surrounded by Windows and Linux.

Windows doesn't have telnet any more, but it's a
"Windows Feature" called "Telnet Client" which you can
activate, i.e. install.

But no need to try telnet because if I try it with the server
you mentioned I get thrown out almost immediately.
Maybe some kind of load balancer or firewall running there.

AND I can ping this server only up to a packet size of 72 (!)
but I can ping other hosts up to a packet size of 5000.

Otoh if I disallow packet fragmentation like this:

then i can only go up to 1472 to other hosts. That's seems to
be the limitation of my firewall.

So... you could try to reduce your MTU to 72 (I've never tried such
a low setting). If that helps it is a problem at or near the destination
host.

Let's see what happens.

Reinhard

---

Hey Reinhard,

Thanks again for all your help, this is a weird one.

I tried setting the MTU to 72 on my RUT but with It on 72, I get no connection to any website. it just grounds to a halt.

With it set back to 1470, I agree with you on that particular website that anything more than 72 gets a fail and yes I had been using gate -D -s command to do my testing previously (Network friend told me to try it!)

What I dont understand is that if I go to my mobile and tether to that, then the site loads immediately. Yet the phone and my home internet are both 4G Vodafone connected to the same cell site so must get the same data etc. The only difference is the Teltonika? Its just so weird!

---

Hi,

in another thread the supporter ZygimantasBliu suggested setting the
MTU for device MOB1S1A1 on the router to 1420 or 1460 and also
Network -> Firewall -> General settings and disable Software flow offloading

Setting the MTU to 1420  seems to have solved the problem for that particular
case. Here is the link to this thread.

Regards,
Reinhard

---

Hey Again Reinhard,

I checked the settings and the Software Flow offloading setting was already set to off.

I've tried setting the MTU back to 1420 but it hasn't made any difference I'm afraid.

I couldn't see the link to the other thread, is it possible to re-send that link so I can see fi there is anything else in there that might be relevant?

---

Sure: just click here, should work.

Or copy/paste this:
https://community.teltonika-networks.com/63931/fire-tv-stick-kein-internet-mit-rutx11

Regards,
Reinhard