SUMMARY: UDP and Solaris Problems

From: William Hiscox (
Date: Sat Jan 07 1995 - 02:31:23 CST

Original Problem:

> I cannot read UDP packets as reliably under Solaris 2.3 (or 2.4) as I
> could under Sunos 4.1.3.
> Info:
> 1. I have side by side sparc 10 model 41s, one running 4.1.3, the other
> 2.4 all on the same subnet. An application designed to read UDP packets
> (from a 3rd machine) runs on both machines. Each UDP packet has an
> embedded sequence number. The 4.1.3 machine does not miss a packet.
> The 2.4 machine misses packets regularily.

Thanks to:

Solution (sort of):

The UDP packets are the result of realtime data collection from 100
sensors located thoughout the United States. These packets funnel
through a PC for distribution. When I switched to a backup PC, the
problem went away (after 2 weeks looking for the problem elsewhere).

I still cannot explain why a solaris machine lost UDP packets, while an
identical 4.1.3 machine had no problems. And I cannot explain the
differences in PCs as they use identical hardware and software. The
problem may lie at a lower level (hardware/firmware and rev levels)
than I am willing to explore.

Suggestions received helped me understand Solaris better:

1. Use of ndd to configure /dev/tcp /dev/udp
2. Differences in 4.1.3 and solaris (udp checksums for example)
3. Use of snoop.
4. The new world of applying and testing patches.

Lesson learned:

1. Connectionless protocols like UDP are important to us. However,
applications that use UDP must be able to detect dropped packets.
Without sequence numbers embedded in each packet, I would never
have known there was a problem.

2. Critical apps need to be tested against any new patches before being
released! My test programs changed behavior after applying patches.

Bill Hiscox


Bill Hiscox Geomet Data Services The National Lightning Detection Network
                        2705 E. Medina Rd #111
                        Tucson, AZ 85706
                        (602) 573-0090 voice
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