Date: Sat, 4 Jan 2003 14:41:38 +0200 (WET) From: Evren Yurtesen <eyurtese@turkuamk.fi> To: =?iso-8859-1?Q?Sten_Daniel_S=F8rsdal?= <sten.daniel.sorsdal@wan.no> Cc: "Wright, Michaelx L" <michaelx.l.wright@intel.com>, fkittred@gwi.net, 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: <Pine.A41.4.10.10301041436440.19242-100000@bessel.tekniikka.turkuamk.fi> In-Reply-To: <0AF1BBDF1218F14E9B4CCE414744E70F07DE29@exchange.wanglobal.net>
next in thread | previous in thread | raw e-mail | index | archive | help
Yes, actually this is why I asked first about MTU settings in wi. I use
PPPoE and it has 8bytes overhead. It could be nice to set MTU to 1508 so
1500 byte ethernet frames can be encapsualted in PPPoE without
fragmentation.
I just dont understand why FreeBSD people have to make this wi driver so
tight in standarts even though there are wireless cards which support
non-standard(and sometimes nice) things which can be useful. I definetely
disagree that something should be in standard so you will allow setting of
it!
For example in /etc/defaults/rc.conf it says
-----------------------------------------------
tcp_drop_synfin="NO" # Set to YES to drop TCP packets with SYN+FIN
# NOTE: this violates the TCP specification
-----------------------------------------------
So why do you let this to violate TCP specifications but you cant let user
to violate ethernet specifications?
Evren
On Sat, 4 Jan 2003, Sten Daniel Sørsdal wrote:
>
> 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
> 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
>
> -----------
> Med vennlig hilsen / Best regards
>
> Sten Daniel Sørsdal
> Wireless Manager
> WAN Norway AS
> -----------
>
>
> -----Original Message-----
> From: Wright, Michaelx L [mailto:michaelx.l.wright@intel.com]
> 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]
> 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
> >
> > Setting a "wireless interface" to a MTU of higher than 1500 octets is
> > ill-advised unless you are in very specific, unusual conditions.
> >
> > The subject header talks about "wi0", which implies IEEE Ethernet
> > 802.11b standard interface.
> >
> > The IEEE maintains the Ethernet standards. Start with:
> >
> > http://www.ieee.org
> >
> > or
> >
> > http://www.ieee802.org
> >
> > >From a quick glance at the standard:
> >
> > "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"
> >
> > it is not clear to me that MTU > 1500 octets are legal with 802.11b.
> >
> > If your system is connected to the Internet, setting the MTU on your
> > 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
> > understand the reasons why, you would be best advised not to mess with
> > the MTU at all.
> >
> > Stick with the default until you gain more experience. You might want
> > to read up on "packet fragmentation" and "MTU discovery" for
> > explanations why this is a good idea.
> >
> > good luck,
> > fletcher
> >
> >
>
>
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-stable" in the body of the message
>
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-stable" in the body of the message
>
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.A41.4.10.10301041436440.19242-100000>