Re: Route cache performance under stress

Re: Route cache performance under stress

[Scott A Crosby]

Please CC me on any replies:


The suggested code here is problematic.

   RND1 = random_generated_at_start_time() ;
   RND2 = random_generated_at_start_time() ;
   /* RND2 may be 0 or equal to RND1, all cases seem OK */
   x = (RND1 - saddr) ^ (RND1 - daddr) ^ (RND2 + saddr + daddr);
   reduce(x)

For instance, if the table is assumed to have size N, bucket
collisions can be generated by:

   saddr=daddr= k*N  for all k.

Or, a different attack, if I assume that reduce(x) determines the
bucket by masking off, say, the lowest 12 bits, then:

   saddr=0xXXXXXAAA
   daddr=0xYYYYYBBB

Where, XXX, YYY are anything, AAA, BBB are arbitrarily chosen.

Now, lets look at the various terms:
 (RND1 - saddr)         = 0xUUUUUCCC
 (RND1 - daddr)         = 0xUUUUUDDD
 (RND2 + saddr + daddr) = 0xUUUUUEEE

The U's are all unknown, but the CCC, DDD, and EEE---the only thing
that we care about---are constant. Thus, the lowest 12 bits of x will
be constant. If those are the only bits that are used, then the
attacker has complete freedom to forge the highest 20 bits of saddr
and daddr.

With that function, you'd probably be better off masking off the high
order bits. At least there's a chance of a carry from the UUUU's
propagating into the bits you mask off.

I'm rusty with statistical analysis of cryptographic algorithms, but I
suspect demons may be lurking from that avenue too.


What might work better is to have a good universal hash function, h,
then do:

   h_k(saddr) - h_k(daddr)

Perhaps the simplest is:

  h_k(x) = x * k (mod P)

where P is a prime, and $ 0<= k < P$ is a random variable determined
at bootup.

Scott

Re: Unsupported VGA card

[John Bradford]

> I am a newbie to Linux. I have a problem. I had Win 2K Pro installed on my
> PC. When I got Red Hat Linux 8.0 installed on it, the it showed "Unsupported
> VGA card", but the rest of the installation went fine. Now, I can log in to
> Linux, and only the command line is seen. When I enter the "startx" command,
> it gives some big error.

This question is more appropriate for a RedHat mailing list.

John.

Unsupported VGA card

[Pratyush Joshi]

Hi everybody,

I am a newbie to Linux. I have a problem. I had Win 2K Pro installed on my
PC. When I got Red Hat Linux 8.0 installed on it, the it showed "Unsupported
VGA card", but the rest of the installation went fine. Now, I can log in to
Linux, and only the command line is seen. When I enter the "startx" command,
it gives some big error.

I have an ASUS P4SDR-VM motherboard with onboard VGA. Probably it is not
supported by Red Hat. What do I do to get KDE/GNOME desktops working ? What
exactly should I look for - is it the display drivers or RPMs ? Can I get
anything from www.kernel.org ? Somebody told me that nVidia's nForce or
gForce drivers should work for ASUS motherboard. Is that true ? In ASUS's
website, I can see display drivers for download, for Red Hat Linux 7.3. Will
those also work for 8.0 ? Are the display drivers specific to the
motherboard make, or the Linux distro and version ?

I am quite confused and would really appreciate a detailed reply.

Thanking you all in anticipation.

With kind regards,
Pratyush Joshi

Re: Unsupported VGA card

[Sahara Workshop]

On Tue, 2003-04-08 at 10:06, John Bradford wrote:
> > I am a newbie to Linux. I have a problem. I had Win 2K Pro installed on my
> > PC. When I got Red Hat Linux 8.0 installed on it, the it showed "Unsupported
> > VGA card", but the rest of the installation went fine. Now, I can log in to
> > Linux, and only the command line is seen. When I enter the "startx" command,
> > it gives some big error.
> 
> This question is more appropriate for a RedHat mailing list.
> 

You might try here:

  http://www.winischhofer.net/sis/

But note that I do not use Redhat, so if questions, direct it to
their mailing lists ...


-- 
Sahara Workshop <workshop@cpt.saharapc.co.za>



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