full-disclosure - Re: (ICMP attacks against TCP) (was Re: HPSBUX01137 SSRT5954

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Message-ID: <Pine.LNX.4.58.0507212024220.27430@screamer.tcp-ip.info>
Date: Fri Jul 22 11:12:43 2005
From: dhudes at hudes.org (Dana Hudes)
Subject: Re: (ICMP attacks against TCP) (was Re:
	HPSBUX01137 SSRT5954

you will find a range of MTU sizes in radio links of various sorts which 
is not just 802.11 but also cellular including GPRS CDMA and WCDMA.
Now, in many instances there is a proxy between the mobile station and the 
public network. In fact I wrote a powerpoint presentation summarizing such 
a paper on transparent TCP proxy in WCDMA and its on my site 
http://www.networkengineer.biz  (I took a course in wireless 
architecture).


On Thu, 21 Jul 2005, Darren Reed wrote:

> In some mail from Fernando Gont, sie said:
> > 
> > At 07:25 p.m. 20/07/2005, Darren Reed wrote:
> > 
> > >In some mail from Fernando Gont, sie said:
> > > > The IPv4 minimum MTU is 68, and not 576. If you blindly send packets 
> > > larger
> > > > than 68 with the DF bit set, in the case there's an intermmediate with an
> > > > MTU lower that 576, the connection will stall.
> > >
> > >And I think you can safely say that if you see any packets trying to
> > >indicate that the MTU of a link is "68" then you should ignore it.
> > 
> > Yes. But what about 296?
> > 
> ...
> > >I think it is reasonable to say anyone trying to advertise an MTU less
> > >than 576 has nefarious purposes in mind.
> > 
> > There are still some radio links with MTUs of 296 bytes.
> 
> Go search with google....people still actively use smaller MTUs.
> 
> What do you do?  Where do you draw the line in the sand?
> 
> Darren
>