Depending of the cisco device .. you could configure a password or aaa access for the first vty lines .i.e line vty 0 2 ( will give you 3 simultaneous telnet sessions ) and then leave the other vty lines with no password ot aaa access line vty 3 15 . Unfortunatley you can do this on a PIX which be default support up to 5 telnet sessions.
As Fernando points out, limiting telnet access involves controlling the vty ports. His suggestion of configuring authentication for some ports and not for others is one approach. I believe that there is a more simple and direct approach. After you decide how many vty lines should be activated, configure this on the vty lines that you do not want to be active:
This will prevent those vty ports from starting an exec session which inherently prevents telnet access to them.
Thanks for the info, right now if I have line vty 0 1 (which should give me 2 telnet connections). However, new VTY lines are being created as needed. I was looking at the line vty session-limit but for some reason that command is not available on any of my equipment (2950's, 3550's, 3560's).
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...