LinkSys LNE100TX overruns

Charles Calkins
Sun Apr 9 14:12:42 2000



  I've recently set up a machine from spare parts to act as a firewall 
(named "firewall") in front of a single machine (named "ako").  firewall
contains a LinkSys EtherFast 10/100 LAN Card which is connected via a category 
5 crossover cable to ako's on-motherboard Intel EtherExpress 10/100.
The 100Mb light and the full duplex light are activated on the EtherFast, yet
performance doesn't seem as good as it should be - I am seeing a high 
receive overrun count on firewall after FTPing test files to it from ako.  Are
overruns an indication that firewall is too slow to process ako's packets,
or is something else amiss?


  ako has 256MB of RAM, is a dual Pentium II-450, and dual boots between 
Windows NT 4.0 SP6 and Linux 2.2.14 (SMP).  firewall has 32MB of RAM (64MB
of swap space), is a dual Pentium-90, and runs Linux 2.2.14 (SMP, compiled 
with most firewalling and masquerading options set).  firewall doesn't run any
system services above and beyond the minimum (load average is 0.00 normally and
doesn't even have X installed) and cat /proc/meminfo indicates the machine has
barely touched swap.
  The driver for the LinkSys card in firewall is tulip.c, v0.90f, and was 
obtained from the LinkSys web site - neither tulip.c as part of RedHat 6.1 or 
the version in 2.2.14 recognized the card due to a different ID (11ad c115).  
(Firewall actually contains two of these cards, but at the present time the 
second is not connected to a network so it has no traffic.)
  When FTPing from ako running NT to firewall I see data rates of about
360KB/s, and from ako running Linux data rates just over 400KB/s.  These 
numbers aren't too bad, but considering its in full-duplex 100Mb mode, I
would expect them to be higher.
  At the moment, ifconfig from firewall shows:

eth0      Link encap:Ethernet  HWaddr 00:A0:CC:36:BD:13
          inet addr:  Bcast:  Mask:
          RX packets:37461 errors:2966 dropped:0 overruns:2966 frame:0
          TX packets:28622 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          Interrupt:9 Base address:0xe800

  so the overruns appear to be an issue with received packets only.  I have 
also tried to reduce the window size of the route from the default to 4096 as 
suggested by a web page - in case ako was providing packets much too quickly 
for firewall - but it had no noticable effect and the overruns still occurred.
  I've performed a few searches of the list archives, but I didn't find any
previously discussed problems relating to overruns.  
  Is a dual Pentium 90 just too slow to work successfully with these cards?  
Does the driver itself benefit from the second processor under 2.2.x kernels?
Is there a newer tulip driver, updated with this chip ID, that would improve

  Thanks for your time - if you could CC responses to me I'd appreciate it
as I'm not currently on the list, though I will monitor the archives.


Charles Calkins
Vice President
Applied Intelligence, Inc.	St. Louis, MO

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