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Author Topic: BT MTU  (Read 15781 times)

hake

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Re: BT MTU
« Reply #15 on: September 10, 2006, 01:29:55 PM »


I only receive IP traffic from connections initiated by my own hosts.  MTU should consequently be what my hosts have negotiated with the hosts that my hosts are connected to.  The MTU should not therefore exceed the size negotiated.  All traffic from hosts I have not sent SYN packets to is rejected so the MTU of unsolicited packets is irrelevant.

That is my understanding of the MTU situation.

If I am wrong (and I often am), I always welcome advice correcting any errors in my understanding since I would rather stand corrected than delude myself that I am right.  TCP/IP is an intensely complicated subject so misunderstandings are inevitable and I rely on others to advise me when they believe that I am in error.

 :-[
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roseway

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Re: BT MTU
« Reply #16 on: September 10, 2006, 04:29:14 PM »

If I am wrong (and I often am), I always welcome advice correcting any errors in my understanding since I would rather stand corrected than delude myself that I am right.
Yes indeed. It can be uncomfortable to have ones own cherished beliefs shot down in flames, but it's certainly better to find out the truth.
I've been known to be wrong too. :'(

Eric
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  Eric

mr_chris

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Re: BT MTU
« Reply #17 on: September 10, 2006, 07:12:25 PM »

As have I, many times!

Quote
I only receive IP traffic from connections initiated by my own hosts.  MTU should consequently be what my hosts have negotiated with the hosts that my hosts are connected to.  The MTU should not therefore exceed the size negotiated.  All traffic from hosts I have not sent SYN packets to is rejected so the MTU of unsolicited packets is irrelevant.

That's right... it will never exceed (a) what you have set on your PC, and (b) what the other end negotiates with you during startup handshake. However there could still be a router somewhere along the line with a lower MTU value which is also blocking ICMP, causing Path MTU to fail. This would then cause packet fragmentation, or worse still, no traversal at all (which is what seems to happen with ebay and microsoft). Lowering the MTU helps overcome this.

You seem to have a pretty sound understanding of TCP/IP and how it works. As you say, it's an insanely complex subject and there's far more to it than meets the eye!
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Chris

hake

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Re: BT MTU
« Reply #18 on: September 10, 2006, 11:48:41 PM »

I like this forum.  I expect to be lowering the tone of it for some time to come.

I like to know how things work.  TCP/IP is a very interesting subject because it is very likely to be the basis of future worldwide communications and because it is very intellectually demanding, especially because it is so dynamic a system.  I will be giving RFC1323 a serious bashing this week.  I might even understand some of it!!!

I won't be making my RWIN more than 65228 (=1418*46) because I have found that the 5+MB bandwidth that adsl max has just given me seems to be more than the capacity of most servers to fill, except for Microsoft's: I downloaded WinXP SP2 (266MB) for fun and the MS server belted it out at 4.5MB.  Most servers seem to be limited to 2MB or less (often considerably less) so I am happy with RWIN appropriate to 2MB.  The fast connection enables my wife and me to surf without slowing each other's traffic.

I have already found the contributions made by forum members to be very valuable to my efforts to further my knowledge and I hope to put something back.

Kitz's RWIN tips really added pzazzz to my adsl connection.  I like it when things work just perfectly and I have a lovely Internet connection now.

I'll shut up now since my posts are becoming irrelevant to this thread.

 :doh:
« Last Edit: September 10, 2006, 11:53:34 PM by hake »
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kitz

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Re: BT MTU
« Reply #19 on: September 11, 2006, 09:14:22 AM »

>> I like this forum.  I expect to be lowering the tone of it for some time to come

and welcome..  we're quite a friendly bunch when you get to know us.


psssst just watch out for those mods roseway and astral in the chat section.. 
I just leave em to it sometimes and go... huh??  :-X
 

>>> I won't be making my RWIN more than 65228
You could go on for ever with tweaking trying different settings..  Im now at the point when.. ok this seems to work well for me.. and I leave it at that.

>>I'll shut up now since my posts are becoming irrelevant to this thread.
hmmmm  you should fit in quite well on this forum then.. 
- see above comment- we're already quite good at doing that :lol:



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roseway

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Re: BT MTU
« Reply #20 on: September 11, 2006, 10:14:59 AM »

Quote
psssst just watch out for those mods roseway and astral in the chat section..
I just leave em to it sometimes and go... huh??

I have no idea what you mean. 8)

Eric
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  Eric

kitz

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Re: BT MTU
« Reply #21 on: September 11, 2006, 10:23:06 AM »

huh??


 :-X
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roseway

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Re: BT MTU
« Reply #22 on: September 11, 2006, 12:55:58 PM »

I was only joking, Kitz. :) :) :) :) :) :) :)
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