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Date:      Sat, 4 Jan 2003 02:13:56 +0100
From:      =?iso-8859-1?Q?Sten_Daniel_S=F8rsdal?= <sten.daniel.sorsdal@wan.no>
To:        "Wright, Michaelx L" <michaelx.l.wright@intel.com>, "Evren Yurtesen" <eyurtese@turkuamk.fi>, <fkittred@gwi.net>
Cc:        "Michael Sierchio" <kudzu@tenebras.com>, <dmagda@ee.ryerson.ca>, <freebsd-stable@FreeBSD.ORG>, <wpaul@ctr.columbia.edu>
Subject:   RE: wi0 and mtu setting [bad idea]
Message-ID:  <0AF1BBDF1218F14E9B4CCE414744E70F07DE29@exchange.wanglobal.net>

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  How about a configuration of two Ad-hoc cards pointing towards =
eachother between two buildings
  and an IPSec tunnel is applied. Wouldn't it be great if (unencrypted) =
packets destined to go through=20
  that IPSec tunnel could go through in full ethernet size, without =
fragmentation, pr host tcp stack
  adjustments or resending because of DF flag?

  What about transporting VLANs over wireless?

  There is a lot of equipment out there, especially wireless but also =
wired (ATM?) that allows larger
  MTUs for special circumstances.

  It's like buying a car with all the extra features - but only a =
handful of the features work.

  Just my 2 nkr=20

-----------
Med vennlig hilsen / Best regards=20

Sten Daniel S=F8rsdal=20
Wireless Manager
WAN Norway AS=20
-----------


-----Original Message-----
From: Wright, Michaelx L [mailto:michaelx.l.wright@intel.com]=20
Sent: 3. januar 2003 19:28
To: Evren Yurtesen; fkittred@gwi.net
Cc: Michael Sierchio; dmagda@ee.ryerson.ca; freebsd-stable@FreeBSD.ORG; =
wpaul@ctr.columbia.edu
Subject: RE: wi0 and mtu setting [bad idea]


Good Afternoon All,

I am curious to know if you are taking into account MTU limitations =
imposed by link-partners i.e. switches, hubs, routers and the like. Some =
if not most ( for Unix) require end-nodes to be approximately 22 bytes =
less than the link-partner device's maximum supported MTU. I am not sure =
if, but would somewhat expect, a wireless access point to have some =
impact on the sizing and/transfer at above the 1500 MTU setting.




Cheers

M. L. Wright
Intel UNIX-NQL
503.264.8300

-----Original Message-----
From: Evren Yurtesen [mailto:eyurtese@turkuamk.fi]=20
Sent: Friday, January 03, 2003 10:07 AM
To: fkittred@gwi.net
Cc: Michael Sierchio; dmagda@ee.ryerson.ca; freebsd-stable@FreeBSD.ORG; =
wpaul@ctr.columbia.edu
Subject: Re: wi0 and mtu setting [bad idea]

You are definetely right, setting the MTU might be really bad thing, but =
why dont you let the person setting it decide it for himself? Thus =
FreeBSD wi driver can support setting this value higher than 1500 in =
your own risk. Its a functionality request only. I dont suggest that you =
set the default mtu for wi driver something higher than 1500!

Evren

On Fri, 3 Jan 2003 fkittred@gwi.net wrote:

> On Fri, 3 Jan 2003 02:22:34 +0200 (WET)  Evren Yurtesen wrote:
> > I definetely agree and obviously since mikrotikos supports this then
linux
> > should do since mikrotikos is built on linux. Why shouldnt FreeBSD
support
> > setting mtu of wireless interfaces higher than 1500
>=20
> Setting a "wireless interface" to a MTU of higher than 1500 octets is=20
> ill-advised unless you are in very specific, unusual conditions.
>=20
> The subject header talks about "wi0", which implies IEEE Ethernet=20
> 802.11b standard interface.
>=20
> The IEEE maintains the Ethernet standards.  Start with:
>=20
> http://www.ieee.org
>=20
> or
>=20
> http://www.ieee802.org
>=20
> >From a quick glance at the standard:
>=20
>   "IEEE Std 802.11b-1999 (Supplement to ANSI/IEEE Std 802.11, 1999
Edition)
>      Supplement to IEEE Standard for Information technology
>      Telecommunications and information exchange between systems Local
>      and metropolitan area networks Specific requirements Part 11:
>      Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
>      specifications: Higher-Speed Physical Layer Extension in the 2.4
GHz
>      Band"
>=20
> it is not clear to me that  MTU > 1500 octets are legal with 802.11b.
>=20
> If your system is connected to the Internet, setting the MTU on your=20
> FreeBSD system, which is probably not a core router, to anything above =

> 1500 is a stupid idea.  If you don't already know this, and don't=20
> understand the reasons why, you would be best advised not to mess with =

> the MTU at all.
>=20
> Stick with the default until you gain more experience.  You might want =

> to read up on "packet fragmentation" and "MTU discovery" for=20
> explanations why this is a good idea.
>=20
> good luck,
> fletcher
>=20
>=20


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