TCP Connection Timeouts for Connections To OS/390

Support knowledgebase (jreuter_s390_ecn)
Applies to

SuSE Linux S/390: Version SLES7

Symptom:

When trying to connect from a suSE Linux Enterprise Server for S/390 and zSeries (both, 31bit-mode and 64bit-mode) to an OS/390 installation an error message "connection timeout" occurs.

Cause:

  1. The service to connect to is not started.
  2. The remote server is not reachable.

Solution:

The connection timeout should only occur in the second case, but due to OS/390 not handling the TCP option ECN (Explicit Congestion Notification) correctly, it also occurs for the first case. Turn off ECN with the following command to get the correct message "connection refused":

echo 0 >/proc/sys/net/ipv4/tcp_ecn

See also:
o Internet Connection: Some Web Sites Cannot Be Viewed

Keywords: ECN, S390, S390X, ZSERIES, S/390, SLES, SLES7, CONNECTION, TIMEOUT

Categories: S/390

SDB-jreuter_s390_ecn, Copyright SuSE Linux AG, Nürnberg, Germany - Version: 10. Jun 2002
SuSE Linux AG - Last generated: 10. Jun 2002 by jreuter (sdb_gen 1.40.0)