After quite a bit of hunting for a tool that would syslog equipment and also capture config changes securely, we decided on Kiwi Enterprises Syslog Daemon and CatTools
Having tested the trial versions some time ago, I was impressed with the pricing and the level of functionality available and even after a bug in the syslogger was identified which was making a bit of a mess of formatting Cisco Pix logs this was fixed by Kiwi while we were still evaluating the trial versions. Very impressive service.
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http://www.nirenet.net/