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Cisco Bug: CSCsz47656 - telnetd shall age out the zombie "half-open" session

Last Modified

May 16, 2018

Products (1)

  • Cisco Carrier Routing System

Known Affected Releases


Description (partial)


Telnet access not working anymore and telnetd processes blocked on tcp :

sh proc block

   Jid       Pid Tid                 Name State  Blocked-on
65723  16093371   1              telnetd Reply  221354  tcp
65729  16093377   1              telnetd Reply  221354  tcp
65763  16081123   1              telnetd Reply  221354  tcp
65764  16101604   1              telnetd Reply  221354  tcp


When a tcp connexion is open to port 23 but the remote client doesn't do telnet option
negotiation, telnetd will keep waiting for telnet option (like terminal type) as far as the tcp
connexion is not closed by the remote end. This comes before the user authentication phase so
doesn't consume a VTY line but will limit the number of concurrent telnet connexions.
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