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Tip of the Month

September 2000

More Classic Network Analysis Tips

Expert systems in protocol analyzers often require expert users! Always get a second opinion usually from yourself. Make sure you understand the underlying reasoning for the suspected "problem" and verify it by careful scrutiny of the packet details and transactions. We have encountered more than one situation where expert systems have misdiagnosed problems, leading the user astray from the correct solution.

When checking a 10BaseT or 100BaseT collision domain (a grouping of hub repeater ports) for CRC errors with an analyzer or cable tester, be sure to check the segment from a port on every hub module (in a chassis or stack). We have seen CRC errors that don't propagate across the entire collision domain; i.e. they only emulate from a certain hub module, so a quick check from an arbitrary hub port, may not show any CRC errors!

When your analyzer asks for a numerical input, such as the data offset for a filter, be mindful of whether you need to input a decimal or a hexadecimal value. Sometimes an analyzer will decode an offset in hex, but require you to enter the value in decimal, or vice-versa. If you have access to Windows, take advantage of the built-in calculator (in scientific mode) or invest in an inexpensive calculator capable of binary/hex/decimal conversion to carry with you along with your analyzer.