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ChristopherPovey
Aspiring Expert
2,524 Views
Message 1 of 9

Broadband Connection More Stable Since Changing MTU...

Since day one of having BT Broadband I have used my own router which is a Vigor 2800.  Though my router is on 24/7 I was seeing that the PPP connection uptime would never be more than 20-24 hours.

 

Recently I changed my MTU value from the routers default to 1500 (to solve an online media server issue).  Just checked my figures today and I see the following:

 

Router Uptime: 173:52:00

WAN Status Uptime: 173:49:54

 

The Uncorrected Block value is a lot smaller now too at 6480 for 138,967,478 RX Blocks (which is a tiny percentage).

 

I am not sure though why the MTU value in the router would affect how stable the connection was, unless the router (or BT Servers) were seeing a lot of fragmented packets and dropping the connection.  Any ideas?


Chris.
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gouledw
Recognised Expert
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Message 2 of 9

Re: Broadband Connection More Stable Since Changing MTU...

The MTU is required because if it is to low, then not enough packets of data will be sent through the logical link, which I would think was causing your Point to Point sessions to drop regularly.  The MTU at the lowest for a stable connection on BT should be around 1472, but the standard is 1500, and most people have no problems with it :).

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ChristopherPovey
Aspiring Expert
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Message 3 of 9

Re: Broadband Connection More Stable Since Changing MTU...


@gouledw wrote:

The MTU is required because if it is to low, then not enough packets of data will be sent through the logical link, which I would think was causing your Point to Point sessions to drop regularly.  The MTU at the lowest for a stable connection on BT should be around 1472, but the standard is 1500, and most people have no problems with it :).


I can't remember what the default value is for the Vigor 2800.  I know I had to change it via Telnet'ing into it.  I think though it might have been less than 1472, which might explain a few things.  Only wish I had changed it months ago! 😞

Chris.
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chris6273
Recognised Expert
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Message 4 of 9

Re: Broadband Connection More Stable Since Changing MTU...

Hmm, I run mine on 1430 and I achieve around 11KB/s faster throughput than I used to on 1458 (On 20CN, I get 859KB/s). Any idea if the 1472 setting is recommended for 20CN or 21CN?

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Distinguished Sage
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Message 5 of 9

Re: Broadband Connection More Stable Since Changing MTU...

1472 was the setting RogerB used to recommend for 20CN - that was a while ago



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ChristopherPovey
Aspiring Expert
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Message 6 of 9

Re: Broadband Connection More Stable Since Changing MTU...

Just checked it again and it has rest PPPoA :(:

 

Router Up Time: 237:40:40

PPPoA Up Time: 23:29:00

 

It is more state than it was though.  I'll see if it manages another 200 odd hours...

Chris.
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Distinguished Sage
Distinguished Sage
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Message 7 of 9

Re: Broadband Connection More Stable Since Changing MTU...

I get that as well but my connection speed on adsl2+ keeps coming back with same speed figures - did yours?



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ChristopherPovey
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Message 8 of 9

Re: Broadband Connection More Stable Since Changing MTU...


@imjolly wrote:

I get that as well but my connection speed on adsl2+ keeps coming back with same speed figures - did yours?


No.  There are two types of connection.  The connection between my router and the exchange equipment has been stable.  My router does not register ADSL drop-outs, but the upload speed has been constant for months.

 

The connection that dropped out roughly every 20-24 hours was the PPPoA connection to BT's servers.  This seems more stable now I have changed the MTU to 1500.

 

I did consider switching the router to the BT HH v2 that I got when I joined BT to see if it improved things.  However, having done research it's configuration for security and QoS is rubbish compared to what I am using now!

Chris.
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mreco99
Newbie
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Message 9 of 9

Re: Broadband Connection More Stable Since Changing MTU...

Hi

 

I have a similar situation, upgrade with BT from 20 to 21CN network, and using a Draytec 2800.

 

Boy did this cause us a drop in service, in terms of speed, connection drops, intermittant speed problems etc.

Anyway, Draytec were helpful, with many firmware tests, now using firmware 2.8.2.1 B1120 and stable

 

But still have slow issues (speedtest.net can show pings between 500 and 12000 sometimes 30 times a day , but often on 47ms)

 

Anyway my MTU was on 1442 until i just changed it to 1500 so will see what happens.

 

Also if you dont have Outbound TCP ACK Prioritize ticked on the draytec you will suffer bad connections.

The BT router doesnt have this option, and is a big problem. I know because ive had a year of complaining and talks with BT including them sending out network experts to independantly test our line (not the usual BT engineer who (no disrespect) often didnt have a clue apart from the one thing he could do with a little test machine (which always gave perfect results!)

 

UPDATE:

 

Uploading a file still causes the PING on speedtest.net to go to 500ms which on the old network never happened.

 

 

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