Kitz Forum

Internet => Interesting Websites => Topic started by: Weaver on December 31, 2015, 03:57:04 AM

Title: MRU / MTU online test website
Post by: Weaver on December 31, 2015, 03:57:04 AM
This service at (
tests your MRU / MTU. A simple-to-use tool, this website just does what it says on the tin. This service is really useful in tracking down potential nagging MRU-related problems if you have changed service type, changed to a two-box system of separate modem and router, or to a different model of separate modem. (See ( for explanation.) It speaks IPv6 too, which I need. Shows a real commitment to quality in design there.

I needed to test whether I could now dare to use full 1500 byte MRU / MTU with my DLink DSL-320B-Z1 modems instead of the annoying restriction to MTU 1492 that you often get with separate modems and PPPoE. When I changed from BTW 20CN to 21CN, I was finally able to use 1500 byte MRU despite having a separate router and PPPoE modem.
Title: Re: MRU / MTU online test website
Post by: Weaver on December 31, 2015, 04:07:11 AM
I notice that the site has a whole lots of other networking tools, a bit of a Swiss Army knife. Very useful
Title: Re: MRU / MTU online test website
Post by: Weaver on February 19, 2020, 05:08:02 AM
I canít get this tool to work. It just hangs for me. I assumed it was my firewalling settings, my Firebrick was not too strict and too paranoid to allow sufficient types of ICMP packets in. So on my iPad I changed to direct 4G, turned off Wi-Fi just to be sure, and thus bypassed my Firewall router, so no firewall at all, but then I still got the same problem. It used to work for me, at one time; Iíve changed my firewalling, but that canít be an issue since Iím not going via that route at the moment.

Can you get it to work for you?

Has it just died for some reason, or is it still me doing something stupid?

Iím now getting an answer when I use it via my firewall, via my router that is, and understandably itís saying it canít get to my own iPad to probe that. However, it could not get to the wan-facing address of my router either, which is more surprising. When I went back to testing my own iPadís 4G i/fís address though, I just get the same old hang. So how does it know?

Iíve noticed that the text inside the [go] button changes, from something like "Test it!" to "TestingÖ", which is not sensible, as you could hit the button twice. It would be better to get rid of the button and put up some plain text instead, or even better still perhaps to go to another page. This current behaviour breaks the back button though, and if you try refreshing the page, it seems brokenness then ensues, presumably as there is still something running on the server. You have to close your web browser to have any chance of resetting the state, it seems, if you want to start a new test. Iím wondering if this is the whole of the source of my problems with it recently. If youíve entered one address, then you cannot change to use another, or perhaps there are still stray processes running on the server and no way of stopping them or cancelling things. Perhaps thereís an enormous hellish timeout somewhere and I am just far too impatient  ;D

I went back to test like this. Close the browser completely. Go to 4G. Retest and then wait an eternity and it works! It does then come back with an answer. It seems the answer is to be careful not to change IP addresses or this confuses it totally.

Still cannot test either WAN-side of router or anything inside the LAN though. (And no, before you ask, my own machines on the lan itself do not have RFC1918 addresses either. They have real global, routable IPv4 and IPv6 addresses. So all good in the sanity dept., for the moment anyway   ;)
Title: Re: MRU / MTU online test website
Post by: j0hn on February 19, 2020, 08:49:36 AM
It won't work if IPV6 is enabled.
Title: Re: MRU / MTU online test website
Post by: Weaver on February 19, 2020, 02:37:46 PM
Ah, that was it. Thanks. Rings a bell now. From a different threadÖ