"\xff" is the Telnet IAC (Interpret As Command) character. If you want to send an actual "\xff" character as data, you need to double it; "\xff\xff" Since it seems you want two "\xff" bytes in a row as data, you need to send 4 "\xff" bytes. See RFC854 pages 13-14.

In reply to Re: sending hexadecimal data via telnet by thundergnat
in thread sending hexadecimal data via telnet by Looserette

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