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Asked: 2026-06-12T14:13:27+00:00

I am connecting to an old device using TcpClient. Initially I am ignoring every

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I am connecting to an old device using TcpClient. Initially I am ignoring every IAC sent by the server. What happens then? Does the server (i.e. the device) assumes its options are accepted or falls to some default settings?

One thing I have noticed is that; there is a byte at the end of almost every message having value 3. Is that normal? To what standart does that fit? (Is it related to Go-Ahead?)

However there is only one exception to what I wrote above (i.e. 3-byte at end of messages) is that one specific type of response always lacks that 3-byte at its end, and I have noticed that when I try to get more bytes I can’t get anything. However if I send a line break (i.e. \n\r) the server sends the rest of the response with a 3-byte at the end. Is that also normal?

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1 Answer

  1. Editorial Team

    The server should proceed with whatever options it said it WILL/WONT do and generally expect that the other side will act as a complete dumb terminal, regardless of requests sent, until such time as it receives a WILL/WONT in reply.

    FF FB 03 would mean IAC WILL SUPRESS-GO-AHEAD, or just continue to send whenever it feels like without waiting for any kind of handshake. It probably does an IAC DO SUPRESS-GO-AHEAD as well.

    If that’s not what you’re asking, a full hex-dump of the communication will be needed.

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