[K12OSN] hub vs. switch at eth0

["Terrell Prudé, Jr."]

David Trask wrote:

>"Support list for opensource software in schools." <k12osn at redhat.com> on
>Monday, August 29, 2005 at 4:47 PM +0000 wrote:
>  
>
>>Why don't you just pull out the Realtek card and that will force the
>>server to use the onboard NIC as eth0?  Sounds like it is an old NIC card
>>that doesn't play well with the Amer switch.  I have seen before where
>>certain NIC's were not compatible with an Amer switch.  So much for
>>standards.  The Amer stuff is pretty low end networking gear and
>>sometimes doesn't work very well.  Is the RealTec NIC a 10/100 or just a
>>10 Mbs NIC?   Sounds like the Amer isn't doing a good job of autosensing.
>>    
>>
>
>Don'ty blame the Amer Switch....I have a whole building full of them 50+
>ranging from little 5 ports to 24 port and gig switches....I also have
>MANY C110W Amer NIC's.  I have a schoolwide LTSP network (600 users) and
>not one issue.  Sounds like the network card may be partly to blame.  Take
>out the NIC and replace with another...try the switch again and then
>see.....you can also try another Amer switch....it's possible you have a
>lemon, but not to worry as it has a lifetime warranty.
>
>  
>

I have, at last, successfully repro'd a variant of this with the SGR24, 
using K12LTSP 4.2.1EL, which I just installed the night before last. 

I got curious and tried a NFS install of K12LTSP 4.2.1EL on my laptop (a 
recent-model Dell Latitude, built-in 10/100).  For some reason, doing 
NFS to my server through the SGR24 resulted in what looked like lots of 
drops and pauses, long enough for there to be some "NFS failure, still 
trying" messages on the client on VTY 4.  Replacing the SGR24 with 
either an eight-port el-cheapo Netgear mini-switch, or the SR48G2i, 
solved the problem.

I then tried a FTP install of SuSE Linux 9.3 with the SGR24, from the 
same server as above (it's running both the NFS server and vsftpd).  The 
results were very different.  It hauled total hiney.  Then, I tried it 
again with another laptop (a newer Dell Latitude with built-in 
10/100/1000), and it, too, worked perfectly.

The only thing I can think of is that NFS is UDP-based by default (it 
still is on my server), and FTP is TCP-based and thus can re-transmit 
dropped packets quickly.  It's kinda reaching, I know, but it's all that 
comes to mind at this point.

But what about booting LTSP terminals?  That's the interesting part of 
all of this...the LTSP terminals that I use, old, generic, beige-box 
Pentium-233's with 3Com 3C905 NICs of various vintages, boot with no 
problem--and quickly!

This looks to me like a subtle timing issue with respect to certain 
implementations of certain 10/100 cards.  Obviously, more testing is 
needed.  More to come!

--TP
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