Wan Mtu Vs Lan Mtu

Kirby Smith · Post by **Kirby Smith** » Sun Feb 03, 2002 4:36 pm

My Nexland ISB SOHO router reports that the WAN speed is 1472 (on a PPPoE connection to Verizon) and that the LAN connection to my PC is 1500. These are either default or negotiated, I'm not sure. Speedguide.net TCP/IP Analyzer detects 1472, as expected, but suggests 1500. I assume it cannot detect that PPPoE is in use.

My question is: Should the PC (Win2k) be adjusted to 1472 also, as well as forcing the SOHO to operate at 1472 to the PC?? Although my download speeds seem to be equal to the 680k Verizon allows, I imagine that if the two MTUs are unequal, the SOHO has to do a lot of repackaging.

Thanks in advance

kirby

P.S. The forum's vBulletin search engine rejects three letter search words, so I couldn't search any of the elements of my title

Lobo · Post by **Lobo** » Sun Feb 03, 2002 4:40 pm

Download SG Optimizer to your desktop, select connection type at top, select optimal settings at bottom, click on apply changes at very bottom and REBOOT
If you wish to enter custom TCP recieve window select custom settings at bottom, enter what you wish, click on apply changes at bottom and REBOOT.
If using Cablenuts adjuster too, you must first bring up adjuster, click on clear all boxes at bottom and reboot, then download and install optimizer.
If you want faster loading of web pages select custom settings at bottom, other settings at top, LAN Speedup=yes, apply changes at very bottom. REBOOT
Select adapter you are using
Optimizer in signature

Kirby Smith · Post by **Kirby Smith** » Sun Feb 03, 2002 4:55 pm

Does this optimizer know what is happening upstream of the PC? And in any case, even if the PC settings are changed, the router might need tweaking. I realize your generic answer is needed for the no-doubt-endless times some variation of my question is asked on this site, but I would like to know the answer to my specific question before I start hacking my registry and router.

kirby

Lobo · Post by **Lobo** » Sun Feb 03, 2002 5:02 pm

First make sure you have newest firmware for your router, router web site, and if you select DSL (PPPoE) on Optimizer it will enter correct MTU which is not 1472

Kirby Smith · Post by **Kirby Smith** » Sun Feb 03, 2002 5:15 pm

I have examined the optimizer. If I follow your directions, I expect to end up with an MTU=1492 LAN connection and an MTU=1472 WAN connection. I don't know if Verizon servers will entertain 1492, although I suppose I could experiment. I will have to recheck the Nexland manual to see if the 1472 is negotiated or default for some reason. That is the real issue. If 1472 is negotiated, then I assume that my PC should be set to the same value, not 1492. -???-

kirby

Lobo · Post by **Lobo** » Sun Feb 03, 2002 5:17 pm

Just do it, it's fine

Kirby Smith · Post by **Kirby Smith** » Mon Feb 04, 2002 12:14 am

The following question and answer was found in the Nexland technical forum.
***************
Q. MTU size is only 1472? I just got the Pro400 and for PPPoE your MTU size is only 1472. Are you looking into changing this to 1492?

Answer from Active Support;

The Pro400 has MTU Discovery and takes the MTU from the ISP when using PPPoE. The PPPoE
negotiation is 8 bytes, the PPP header is 20 bytes. From the Ethernet maximum MTU 1500,
minus these 28 bytes, the remainder is 1472. That is why this number can not be altered.
****************

This differs from everything I have read on this site. Arrgggghhhhh!

kirby

Lobo · Post by **Lobo** » Mon Feb 04, 2002 9:36 am

Just so happens we are right, have had no complaints, do what you wish, if you use or product and don't like it, uninstall it

Bob Carrick · Post by **Bob Carrick** » Mon Feb 04, 2002 9:46 am

1) Launch your browser
2) In the "Address" bar in your browser type"192.168.0.1" -> Hit "Enter"
3) Click on "Expert Level"
4) Edit the "MTU Wan Port", default is 1472 do not go any higher then 1492.

You can set an MTU of 1492 with a Nexland router, PPPoE MTU in most cases should be 1492.

Kirby Smith · Post by **Kirby Smith** » Mon Feb 04, 2002 3:17 pm

Any idea what these 20 bytes are that Nexland is asserting are needed, which I interpret to mean they are packing on top of the data and its header?

Lobo:
I am not attacking the Optimizer or you. The Optimizer looks extremely useful and well laid out. I'm sure it does what it shows. I am trying to understand what is going on. Bob's response suggests that it would not be sufficient to just change the PC MTU, or even the router's LAN MTU, without also adjusting the WAN MTU to be consistent. With Nexland claiming they need to add 20 bytes of PPP header, presumably (but perhaps not) in addition to the MTU-MSS 40-byte header, then a 1492 MTU would obviously overrun the 1500 byte limit. Setting everything to 1492 may well work, and I will certainly experiment with it when I have time, but surely you see a discrepancy here. Perhaps Nexland are prepending data that other routers do not. I bought my Nexland ISB SOHO solely on the basis of the rave review at this site. I would _hope_ that Nexland's technical support and Speedguide.net's gurus could agree on what the PPPoE MTU size has to be. If this Nexland issue has been addressed in some other forum topic that you mistakenly assume I am deliberately ignoring, please give me a pointer to it.

kirby

Bob Carrick · Post by **Bob Carrick** » Mon Feb 04, 2002 3:25 pm

It seems all companies use a different MTU for PPPoE, I think it is how you read the RFC for PPPoE. IE: EnterNet uses 1454, the RF states 1492, but Windows XP uses 1480, and Nexland goes with 1472. I wish I could explain, I can get further details from Nexland since I'm in close contact with them.

Kirby Smith · Post by **Kirby Smith** » Mon Feb 04, 2002 6:46 pm

If we don't know what Nexland's definition is, then we don't know what Nexland "MTU" value will get us to _our_ definition of 1492 + 8 = 1500. Or, to put it another way, I don't know what Optimizer MTU value will set the PC packets to conform to a given Nexland MTU value. All this, of course, begs the question of what Verizon's DSL multiplexer is expecting when it negotiates with the router.

Thanks for whatever clarification you can eke out of Nexland.

kirby

Bob Carrick · Post by **Bob Carrick** » Mon Feb 04, 2002 6:50 pm

I've dropped my buddy there an e-mail, luckily it is the president of the company. I can expect a responce of some sort within the next 24 hours.
I asked why 1472, and what the router does when a packet from the LAN comes in at 1500.

Kirby Smith · Post by **Kirby Smith** » Tue Feb 05, 2002 5:51 pm

...kirby

Bob Carrick · Post by **Bob Carrick** » Tue Feb 05, 2002 5:53 pm

I just sent a follow up e-mail to find out why I have not gotten a response (It's only been 24 hours, so I guess I should be more patient).

cave · Post by **cave** » Tue Feb 05, 2002 7:03 pm

hi Bob Carrick

do you know why if i set my linksys router to 1500 for mtu i drop conntion

Bob Carrick · Post by **Bob Carrick** » Tue Feb 05, 2002 7:19 pm

I'm going to assume you are on a PPPoE based connection or you wouldn't be asking me. 1492 is the maximum on a PPPoE based connection (8 bytes are needed for PPP header), hence you need 1492, and 1500 won't work.

Post by **Philip** » Tue Feb 05, 2002 7:25 pm

Originally posted by Bob Carrick
I just sent a follow up e-mail to find out why I have not gotten a response (It's only been 24 hours, so I guess I should be more patient).

Tell Greg hello from me as well, I'd like to know too.

Bob Carrick · Post by **Bob Carrick** » Tue Feb 05, 2002 8:05 pm

Will do

Bob Carrick · Post by **Bob Carrick** » Wed Feb 06, 2002 11:22 am

I've had two calls from Nexland this morning, the detailed discription as to why a Max MTU of 1472 is on it's way to me, when i get it I will post it.

Kirby Smith · Post by **Kirby Smith** » Wed Feb 06, 2002 12:15 pm

Thanks. Looking forward to the information, from which I hope we can determine what MTU should be on the LAN side.

kirby

Bob Carrick · Post by **Bob Carrick** » Wed Feb 06, 2002 1:25 pm

Oh that they have already told me. Your LAN MTU SHould match your WAM MTU, if not all SOHO routers (Anything under $1800 they said) would fragment the packets.

Post by **Philip** » Wed Feb 06, 2002 2:06 pm

How about the default 1472 value ?

Bob Carrick · Post by **Bob Carrick** » Wed Feb 06, 2002 2:07 pm

That is what I'm waiting on from the technical e-mail I'm told I will be getting. Because I have been arguing with them as to why, so they are sitting down with their engineers to find out exactly why the engineers chose 1472.

Kirby Smith · Post by **Kirby Smith** » Wed Feb 06, 2002 5:50 pm

If the optimal WAN/LAN value is 14XY, the order in which I change parameters should be what? Let me guess the following:

a) I shut down my ADSL modem and change the Nexland WAN value to 14XY, unless XY is 1472 where it is now.

b) I change the Nexland LAN value to 14XY. When I hit the "change" button (I think it is called) I expect I may loose communication with the router at this point. In any case, I think I have to reboot the router and turn on the ADSL modem.

c) I then run optimizer on my Win2k PC after setting it to 14XY and some appropriate Rwin value.

d) I reboot the PC and see if I can communicate with anything.

Please advise if you see an inherent flaw or a better order of correction.

Thanks

kirby

Bob Carrick · Post by **Bob Carrick** » Wed Feb 06, 2002 6:00 pm

You can test your connect without setting the MTU on the PC, it will just fragment packets, but should still work. Then set the MTU on your PC to match your router and an RWIN to correspond, so ya you seem to have it all down.

Kirby Smith · Post by **Kirby Smith** » Thu Feb 07, 2002 12:24 pm

Originally posted by Bob Carrick
Oh that they have already told me. Your LAN MTU SHould match your WAM MTU, if not all SOHO routers (Anything under $1800 they said) would fragment the packets.

A quick test this morning using the Optimizer confirms this. The highest unfragmented packet size was 1472. This was with the router unchanged from its state at the beginning of this thread (WAN = 1472; LAN = 1500).

kirby

BlackSword · Post by **BlackSword** » Fri Feb 08, 2002 12:01 pm

^Bump,, any answer from Nexland Bob?

Bob Carrick · Post by **Bob Carrick** » Fri Feb 08, 2002 12:06 pm

Not the official answer I'm waiting for no, I've got a couple issues in with them now, all basically concerning the same MTU issue, so they are working on them all at once, one could be found as a problem with MTU padding in Nexland routers, so I assume they are testing it. I left a voice mail today to remind them...

BlackSword · Post by **BlackSword** » Fri Feb 08, 2002 3:07 pm

Thanks for the update,,, still waiting eagerly

Kirby Smith · Post by **Kirby Smith** » Sun Feb 10, 2002 11:32 am

I ran the Optimizer at 1472 after setting the router to 1472 on the LAN side. All seems well. I haven't tested exact performance, but as I didn't have a speed problem before, I probably won't notice a vast improvement.

Philip:
On pushing the "Apply Changes" radio button, I got a message window that said "Please waiting ...to boot" or something like that. I think your message must have been changed but only part of the change took.

kirby

Post by **Philip** » Sun Feb 10, 2002 12:38 pm

Originally posted by Kirby Smith
I ran the Optimizer at 1472 after setting the router to 1472 on the LAN side. All seems well. I haven't tested exact performance, but as I didn't have a speed problem before, I probably won't notice a vast improvement.

Philip:
On pushing the "Apply Changes" radio button, I got a message window that said "Please waiting ...to boot" or something like that. I think your message must have been changed but only part of the change took.

kirby

The programmer that's helping me with the Optimizer doesnt speak much English... So much for his grammar, lol. Will be fixed.

Kirby Smith · Post by **Kirby Smith** » Tue Feb 12, 2002 7:53 pm

and Bob hasn't reported Nexland's answer on why they use MTU = 1472. I conjecture one of the following is true:

a) No one there remembers why it was 1472
b) They internally disagree over the proper MTU size
c) They are trying to find out if all PPPoE ISPs conform to the RFC before answering
c) They agree it should be 1492 but are embarassed to admit it, or
d) They are too busy with bigger problems to send Bob their considered opinion.

Anyone for bets?

kirby

Bob Carrick · Post by **Bob Carrick** » Tue Feb 12, 2002 7:57 pm

They answered all my questions but this one, actually they did answer why 1472, but I disagreed with them, as I've read the RFC, and that lead to a reply of I will had to read the RFC and figure this out. I will find out why they have not answered me.

Post by **Philip** » Tue Feb 12, 2002 8:24 pm

Many earlier routers had the MaxMTU reduced... It was somehow related to "corrupted downloads", where the client would receive the files but some would fail CRC check.

I'm not sure if this is the case, just thought it might be related.

BTW, the new generation Nexland routers I've seen do have the option to specify MTU size explicitly (from the web configuration screens), I'm behind a ISB-SOHO right now with an MTU of 1500.

Bob Carrick · Post by **Bob Carrick** » Tue Feb 12, 2002 9:55 pm

The new routers have the option, but on PPPoE will not let you got higher then 1472, though you can lower it. The explination Was 8 bytes for PPPoE and 20 bytes for PPP, but the RFC clearly states 8 bytes, we are determining where they got this additional 20 figure. Such as Windows XP's 1480 MTU (For 20 bytes for header), EnterNet's 1454, everyone differs though the RFC clearly states 8 bytes.

Bob Carrick · Post by **Bob Carrick** » Wed Feb 13, 2002 12:48 pm

I've gotten the unoffical responce and was asked not to pubilsh it until I get the official responce, so at least we are getting somewhere.

BlackSword · Post by **BlackSword** » Wed Feb 13, 2002 1:07 pm

Originally posted by Bob Carrick
I've gotten the unoffical responce and was asked not to pubilsh it until I get the official responce, so at least we are getting somewhere.

good work Bob,, I appreciate you following up on this issue! Thanks!

Kirby Smith · Post by **Kirby Smith** » Wed Feb 13, 2002 6:40 pm

Yes, thanks for the persistence. And I guess thanks to Nexland for responding to it.

kirby

Kirby Smith · Post by **Kirby Smith** » Sun Feb 17, 2002 10:56 am

Did Nexland provide an estimate of when the official reply would be made?

kirby

SG Broadband Community

Wan Mtu Vs Lan Mtu

Wan Mtu Vs Lan Mtu

Thanks Lobo

Further thanks!

And from Nexland....

Thanks Bob

I would greatly appreciate that, Bob

I wait with bated breath.....

help

Kudos to you, kind sir!

So, the order of modification should be....?

As expected...

All your base are belong to us?

Re: All your base are belong to us?

Well, its been 8 days since Nexland was first pinged....

Bob?