MTU/MSS Clamping and speedtests

[L2020]

New to IDNet with FTTP 1000/115. 

Noticed that MTU was showing as not optimised when visiting https://www.speedguide.net/analyzer.php and is at 1460, previous ISP's I've been at it was always 1492 and with a quick tweak to use baby jumbo packets (MTU 1508) to get MTU up to 1500, so fully optimised.  I've Googled and see this has been a common observation with IDNet all the way back to 2008. 

I've done a packet capture and what is happening is somewhere on IDNet network they are modifying the TCP setup and changing the sources advertised MSS @ 1460 to 1420.  There is no issue with packets at up to 1500 on IDNet as it is possible to ping with packets at that size without fragmentation.  Seems a bit odd in 2020 to be MSS clamping in this way on a FTTP/FTTC internet connection.  Just wondering what the rational was for this if anyone knows.

Speedtests (all over wired Ethernet): so at my last ISP on FTTP @ 330 I would get a pretty consistent ~ 280Mbps on the Thinkbroadband single thread test then > 290Mbps on the multi-thread test.  With IDNet the single speed test is often much lower, never more than around 300 and often drops down as low as 150.  The multi-thread test I'm lucky to see 450.  If I use a few select servers at Speedtest.net then I can see ~700 on a single thread test and ~900 on a multi-thread test so much better, although mostly servers there struggle to get above 400 but that could be a limit of the other end, I have no way of knowing.  Given though that IDNet link to the Thinkbroadband speedtester from my dashboard I was surprised it does so poorly.  I've seen many people post speeds of >900 at Thinkbroadband with other ISPs so their tester is capable of maxing out a connection, so I think I'm up against a bottleneck or congestion somewhere, and considerably so if speeds are dropping as low as 150Meg for a 1Gig FTTP service.  I've repeated the tests at Thinkbroadband with a direct PPPoE connection to the ONT and same results.

Granted outside of speedtests there are going to be few occasions (certainly at this point in time) where we max out these 1Gig FTTP connections, but it would be good to know the capacity is there for the odd time we connect somewhere that can utilise a lot more of the bandwidth.   On the plus side the upload speed is consistently around 115Mbps which is great for work.

[Simon]

I'm afraid that's all a bit too technical for me, but welcome to the forum.

It's might be worth raising those issues with IDNet directly, as they could probably give you first hand insight.  They don't bite.  🙂

support@idnet.net

[john7]

I noticed this ands checked my MTU, it was all setup, pC, Router and Modem at 1500 and worked at that under my foremer ISP. Its now 1460 as well. I also will try support but it does rather look rather than the claimes of no caps there are some in place.

[L2020]

I noticed this ands checked my MTU, it was all setup, pC, Router and Modem at 1500 and worked at that under my foremer ISP. Its now 1460 as well. I also will try support but it does rather look rather than the claimes of no caps there are some in place.

Seems that this issue has been resolved and clamping has now been removed, so currently MTU is available up to the more optimised 1500, at least showing that way for me on tests and at speedguide.net TCP analyser.  Thanks to whoever picked this up or worked with support on it.