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rhysjenz

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#115534 28-Mar-2013 19:26
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Hi there, we've just switched to Telecom from Orcon (because I couldn't be bothered getting Orcon to switch us to a cabinet connection/don't really rate them).

Anyway, we've been hooked up, and definitely have a solid ADSL2 connection to our local cabinet. Almost everything that uses Internet works, except for browsing the web. That said, some particular websites still work for some reason.

Stuff that works: Skype, Xbox Live, downloading/updating apps on iPhones/iPads, downloading within iTunes, YouTube (on mobile and browser), Facebook (usually), anything Google (googling's fine, same with Gmail, and Drive).

Stuff that doesn't work: most web pages. When on the phone with Telecom the ones we were continually testing and troubleshooting were vimeo.com, speedtest.net, and chainreactioncycles.com. These were confirmed not to load with 2 laptops, an iPhone, and a iPad, so I guess it's not particular device settings.

When it is working, it's fast. Downloads/updates were speedy. The Speedtest.net app works, and was getting ~15mbps down, which is pretty sweet compared to the ~3mbps we were getting with Orcon connected to the exchange.

Telecom were pretty stumped. Their base support elevated it to some other guy, who I spent ages with troubleshooting. In the end he was stumped and got me to send them a copy of the results of various tracert and ping commands. Apparently it's been handed to somewhere else at Telecom to have a look at.

Apparently they'll get back to us in 5 working day (if they can even find a solution...), which sucks, so I thought I'd post something here and see if anyone could help. If you need any info or settings or whatever please fire away and I'll be onto it asap. Thanks!

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rhysjenz

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  #789218 29-Mar-2013 12:50
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Wow okay so I changed the MTU in the router settings to 1500, and lo and behold, web browsing now works!
I ran a couple speedtests, and am getting ~30ping/~10down/~1up, seems to be working fine.
Thanks for the help guys (especially cbrpilot), you did better than Telecom :)

PS: What was going on there? Telecom actually says to use 1492 so...? TL;DR of what was wrong? Thanks again.



cbrpilot
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  #789225 29-Mar-2013 13:14
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rhysjenz: Wow okay so I changed the MTU in the router settings to 1500, and lo and behold, web browsing now works!
I ran a couple speedtests, and am getting ~30ping/~10down/~1up, seems to be working fine.
Thanks for the help guys (especially cbrpilot), you did better than Telecom :)

PS: What was going on there? Telecom actually says to use 1492 so...? TL;DR of what was wrong? Thanks again.


You're very welcome.  Have to give some credit to l43a2 who first suggested it may be an MTU issue - and your symptoms did very much fit with that sort of issue.

I cannot be sure of what was occurring, but it is very possible that something funky was going on with the PPP LCP negotation where the MTU/MRU is exchanged/agreed between the BNG and modem.  I.e. the modem said one thing, and did another?
Either that or it does not support MSS-clamping.  Probably the later.  

The way this works is that your PC (and other devices) talking out an Ethernet or Wifi interface assume that everything on the other side of the interface supports a full 1500 byte frame.  When the internet link is only set to 1492 rather than 1500, this presents an issue.  Some sites will work as they allow their packets to be fragmented, others don't.  Most modems support MSS-Clamping which is where the modem intercepts the TCP session setup and forces both ends to negotiate a smaller packet size.  It may be that your doesn't?

I'm not sure why the Telecom site recommends 1492.  1492 is the correct size for an older PPPoE implementation.  Chorus doesn't use PPPoE on their customer facing interfaces - they're all PPPoA (with a couple of exceptions).   I'd say the information on that page was produced a very long time ago, and no-one has ever questioned that piece of information (probably, to be honest, because very few people understand it).

I'll have a chat to some people on Tuesday and see if I can get that page updated.

I have been known to work for Telecom, but I'm not here as an official representative or anything.




My views are my own, and may not necessarily represent those of my employer.


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