I'm working in an area with industrial cellular IP modems such as ones from the company Four Faith. A manual is available from the URL

On page 27/40 it describes a setting called "Transfer meaning". When it's enabled it will apply a transformation to hex 0xfd and 0xfe. It will change the respectively characters to 0xfd 0xed and 0xfd 0xee.

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This option is quite in various products. I'd like to understand why this option is used? For example, is it because there are routers with protocol identifiers which require this setting?

I'm interested in understanding the potential risks with disabling this feature?

  • I'm aware that Telnet uses 0xfd and 0xfe for DO and DONT respectively. Is there any other usage? – sdbol Oct 29 '20 at 3:05

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