DoS of LAN via D-Link switches

["Frank Bures" <lisfrank () chem toronto edu>]

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D-Link switch Model: DSS-16+

When user connects the same patch cable to two ports of the switch, the
switch will ultimately bring down hierarchically higher branches of the 
LAN.

We have this D-link local switch connected to a 3COM 3300 family switch. A
user connected a patch cable to two ports of the D-Link switch effectively
shorting them together.  The switch started to send out large packets that
would periodically overwhelm the 3COM 3300 switch and propagate father
through the network.

The first symptom of this phenomena were log entries from Linux machines
running ntpd complaining about "too many recvbufs allocated".  Those
machines were on the LAN way beyond the shorted D-Link switch.  The 
problem kept spreading through the LAN and it finally took down three SGI 
Octane machines running IRIX 6.5, effectively DoSing them from the network.  
There were problems with NFS and other services, again way beyond the 
initial D-Link and its connected 3COM switch.  The 3COM 3300 switch 
connected directly to the "shorted" D-Link switch became unusable together 
with the part of the LAN it serves.

In my opinion, a switch should be immune to this admittedly insane
manipulation.  Otherwise, one can DoS the entire network just by shorting
two RJ-45 network outlets in one's office together.

Ours is a rather large LAN.  One part of it is served by Extreme Networks 
switches.  None of the SGI machines behind these switches were affected by 
the short.  In fact no adverse effects were observed in that part of the 
LAN.

I contacted the D-Link with the description of the DoS.  They have no record 
of a similar report on file.  They offered no solution.


Frank Bures, Dept. of Chemistry, University of Toronto, M5S 3H6
fbures () chem toronto edu
http://www.chem.utoronto.ca
PGP public key: http://pgp.mit.edu:11371/pks/lookup?op=index&search=Frank+Bures
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