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SubjectLarge numbers of TCP resets
Date
Recently, the web-app at the company I work for started having problems load 
balancing. This was traced back to a large number of tcp-resets being sent
from the web servers to the clients.

Here's netstat output for one of the boxen:
437761 active connections openings
0 passive connection openings
21 failed connection attempts
0 connection resets received
101 connections established
140497907 segments received
149967684 segments send out
116610 segments retransmited
111 bad segments received.
1003306 resets sent

This box is running an apache/tomcat/jboss setup serving both HTTP and RMI
requests. The reset packets disrupt the load balancing method, as the load
balancers think the reset means the connection can now be round-robined to the
next machine. This can be masked by using cookie-based balancing, but I am
worried that we would be masking a problem.

Documentation concerning tuning buffers for network purposes say that 2.4 is
good at auto-tuning, and that only /proc/sys/net/ipv4/tcp_wmem|tcp_rmem might
need tweaking.

The kernel is 2.4.9-31smp from RedHat 7.2. The cards are Intel 82557's. There
are two interfaces, with 1 for client access and 1 used for communication with
the backend database. (The ->client is the one we are worried about).

Any ideas on why the interfaces would be doing this? The boxes served 1.6
hits/sec average over last month for a total of about 10Gb. Is there some
tuning that needs to take place?

Thanks in advance.

Cory 'G'
Watson


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