Ideal MTU for BT Max ADSL

Hi


Does anyone know what this should be?
Is it necessary to set it explicitly on the PC's as well as the router?


My router default MTU is 1500.
This worked fine on one (XP) PC, but another PC on the network could not access certain sites, such
as hotmail. Some applications such as a secure shell client could not connect.


On advice I changed the MTU on the router to 1458, and the MTU on the PC's to 1438.

Both PC's can now access all sites, and SSH works.
But the download speed seems to have dropped.


Any advice or pointers gratefully received...


TIA - Adam

Download tcpoptimizer. Works out the ideal MTU and optimizes your broadband
connection.

Adam Lipscombe wrote:
> Hi
>
>
> Does anyone know what this should be?
> Is it necessary to set it explicitly on the PC's as well as the router?
>
>
> My router default MTU is 1500.
> This worked fine on one (XP) PC, but another PC on the network could
> not access certain sites, such as hotmail. Some applications such as a
> secure shell client could not connect.
>
>
> On advice I changed the MTU on the router to 1458, and the MTU on the
> PC's to 1438.
>
> Both PC's can now access all sites, and SSH works.
> But the download speed seems to have dropped.
>
>
> Any advice or pointers gratefully received...
>
>
> TIA - Adam

Some handy info here:-
http://www.kitz.co.uk/adsl/tweak2.htm

Kind Rgds,

--
|Bob Pullen Broadband Solutions for
|Support Home & Business @
|PlusNet plc. www.plus.net
+------ PlusNet - The smarter way to Internet! ------

On Mon, 26 Mar 2007 11:39:47 +0100, Adam Lipscombe
<(E-Mail Removed)> wrote:

>Hi
>
>
>Does anyone know what this should be?
>Is it necessary to set it explicitly on the PC's as well as the router?
>
>
>My router default MTU is 1500.
>This worked fine on one (XP) PC, but another PC on the network could not access certain sites, such
>as hotmail. Some applications such as a secure shell client could not connect.
>
>
>On advice I changed the MTU on the router to 1458, and the MTU on the PC's to 1438.
>
>Both PC's can now access all sites, and SSH works.
>But the download speed seems to have dropped.
>
>
>Any advice or pointers gratefully received...
>
>
>TIA - Adam

I would have thought that the best MTU for BT was 1500, unless you're
using a Draytek and then it's 1492 or you can't access some sites.

You may also need to increase RWIN.

Useful information here http://www.kitz.co.uk/adsl/MTU2.htm

"Adam Lipscombe" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> Hi
>
>
> Does anyone know what this should be?
> Is it necessary to set it explicitly on the PC's as well as the router?
>
>
> My router default MTU is 1500.
> This worked fine on one (XP) PC, but another PC on the network could not access certain sites, such
> as hotmail. Some applications such as a secure shell client could not connect.
>
>
> On advice I changed the MTU on the router to 1458, and the MTU on the PC's to 1438.
>
> Both PC's can now access all sites, and SSH works.
> But the download speed seems to have dropped.
>
>
> Any advice or pointers gratefully received...
>

Providing that your router is set to use PPPoA VC-Mux,
an MTU of 1478 has the lowest overheads and an MTU
of 1430 is virtually as good.

Either value should give you very slightly better speeds even than an
MTU of 1500.

The reason for this is that packets are broken up and sent
in fixed length ATM cells with padding bytes added to fill
any unused space in the last cell.