odd behavior of telnet server

[Martin T <m4rtntns () gmail com>]

Hello,
I have a radio device which supports management over telnet. However,
it supports only one telnet session at a time. If I do "hping -S -p 23
-i 5 -I fxp0 10.10.10.1"(send TCP SYN packet to port 23 of 10.10.10.1
after every 5 seconds over interface fxp0) I get following tcpdump
output:

17:08:19.121008 IP 10.10.10.2.2606 > 10.10.10.1.23: Flags [S], seq
1136245793, win 512, length 0
17:08:19.133181 IP 10.10.10.1.23 > 10.10.10.2.2606: Flags [S.], seq
1563478181, ack 1136245794, win 16, options [mss 1460], length 0
17:08:22.133596 IP 10.10.10.1.23 > 10.10.10.2.2606: Flags [S.], seq
1563478181, ack 1136245794, win 16, options [mss 1460], length 0
17:08:24.132074 IP 10.10.10.2.2607 > 10.10.10.1.23: Flags [S], seq
1100619793, win 512, length 0
17:08:24.140696 IP 10.10.10.1.23 > 10.10.10.2.2606: Flags [R], seq
1563478182, win 16, length 0

Any ideas why my 10.10.10.2 machine doesn't reply to SYN+ACK packet
from 10.10.10.1? Instead 17:08:24.132074 it sends another TCP SYN
packet and then I get reset from radio device(10.10.10.2). I don't see
such behavior with any other telnet server.. Any ideas?


regards,
martin
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