MTU and RWIN

It seems that the MTU is a function of the router, but that RWIN is a
function of the connected computer. Is that correct?

If so, does that mean you have to set up the RWIN on each computer that
is plugged into the router?
--
Chris

In message <aIHQuVAV2YtDFwdJ@[127.0.0.1]>, Chris <nospam@[127.0.0.1]>
wrote
>It seems that the MTU is a function of the router, but that RWIN is a
>function of the connected computer. Is that correct?
>
>If so, does that mean you have to set up the RWIN on each computer that
>is plugged into the router?


<http://www.dslreports.com/faq/tweaks?text=1>

--
Alan
news2005 {at} amac {dot} f2s {dot} com

Chris wrote:
> It seems that the MTU is a function of the router,

I would leave the router alone (though you could do it on the router)
and change each PC - 1478 is best for normal UK dsl.

but that RWIN is a
> function of the connected computer. Is that correct?
>
> If so, does that mean you have to set up the RWIN on each computer that
> is plugged into the router?

Yes.

Andy.

Andy Furniss wrote:

> I would leave the router alone (though you could do it on the router)

Thinking more I would say just doing it on the router will be at best
only partially effective (mtu on wan facing will only affect upstream),
at worse will break some sites (mtu on lan facing if < on PC will fail
if the site ignores icmp frag needed - and many do).

What I think at 2am is often wrong though :-)

Andy.

On Sat, 31 Dec 2005 01:41:41 +0000, Andy Furniss
<(E-Mail Removed)> wrote:

>I would leave the router alone (though you could do it on the router)
>and change each PC - 1478 is best for normal UK dsl.

I would leave everything at the standard 1500, personally.

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.

On Sat, 31 Dec 2005 01:41:41 +0000, Andy Furniss
<(E-Mail Removed)> wrote:

>I would leave the router alone (though you could do it on the router)
>and change each PC - 1478 is best for normal UK dsl.

I get packet fragmentation at anything above 1458.

--
Cheers,

Guy

** Stress - the condition brought about by having to
** resist the temptation to beat the living daylights
** out of someone who richly deserves it.

On Sun, 01 Jan 2006 16:38:47 +0000, Dr Teeth
<(E-Mail Removed)> wrote:

>
>I get packet fragmentation at anything above 1458.

ISP or kit specific ?

C:\Documents and Settings\Phil.XP2100>ping www.bbc.co.uk -l 2000

Pinging www.bbc.net.uk [212.58.224.88] with 2000 bytes of data:

Reply from 212.58.224.88: bytes=2000 time=96ms TTL=248
Reply from 212.58.224.88: bytes=2000 time=94ms TTL=248
Reply from 212.58.224.88: bytes=2000 time=95ms TTL=248
Reply from 212.58.224.88: bytes=2000 time=99ms TTL=248

Ping statistics for 212.58.224.88:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 94ms, Maximum = 99ms, Average = 96ms

on Demon

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.

Phil Thompson wrote:
> On Sun, 01 Jan 2006 16:38:47 +0000, Dr Teeth
> <(E-Mail Removed)> wrote:
>
>
>>I get packet fragmentation at anything above 1458.
>
>
> ISP or kit specific ?
>
> C:\Documents and Settings\Phil.XP2100>ping www.bbc.co.uk -l 2000
>
> Pinging www.bbc.net.uk [212.58.224.88] with 2000 bytes of data:
>
> Reply from 212.58.224.88: bytes=2000 time=96ms TTL=248
> Reply from 212.58.224.88: bytes=2000 time=94ms TTL=248
> Reply from 212.58.224.88: bytes=2000 time=95ms TTL=248
> Reply from 212.58.224.88: bytes=2000 time=99ms TTL=248
>
> Ping statistics for 212.58.224.88:
> Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
> Approximate round trip times in milli-seconds:
> Minimum = 94ms, Maximum = 99ms, Average = 96ms
>
> on Demon
>
> Phil
Aren't you missing the -f flag? (eg. ping www.bbc.co.uk -f -l 2000)

On Mon, 02 Jan 2006 10:12:40 +0000, David <(E-Mail Removed)> wrote:

>Aren't you missing the -f flag? (eg. ping www.bbc.co.uk -f -l 2000)

no, I was being obscure - does that work for you without the -f ?
tried it on other websites ?

www.demon.net won't ping with 2000 packets, www.demon.co.uk will.

it shouldn't be necessary to adjust a PC down to the MTU that doesn't
fragment, as that is what PMTUD is supposed to do.

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.

Phil Thompson wrote:
>
> no, I was being obscure - does that work for you without the -f ?
> tried it on other websites ?

yes, it works on www.bbc.co.uk and works on some others but not all

>
> www.demon.net won't ping with 2000 packets, www.demon.co.uk will.
>

agreed

> it shouldn't be necessary to adjust a PC down to the MTU that doesn't
> fragment, as that is what PMTUD is supposed to do.
>
> Phil

perhaps I've misunderstood but if you're trying to discover the maximum
MTU to use don't you need to use the -f flag to highlight when
fragmentation is occuring? In your example of www.bbc.co.uk, it echo's
the ping but you don't know that it's fragmenting without the -f.