Former Cisco Systems CEO John Chambers learned all about technology’s volatile highs and lows as a veteran of the internet’s early boom days during the late 1990s and the ensuing meltdown that followed the mania.

And now he is seeing potential signs of the cycle repeating with another transformative technology as a whirlwind of investments and excitement about artificial intelligence has propelled the stock market to new highs.

Chambers took a similarly meteoric ride in his early days running Cisco, which had a market value of about $15 billion in 1995, when networking equipment suddenly became must-have components for the buildup of the internet. The feverish demand briefly turned the firm into the world’s most valuable company — worth $550 billion in March 2000 — before the investment bubble burst. The crash caused Cisco’s stock price to plunge more than 80% during a period that Chambers still recalls as the worst of his career.

Cisco bounced back to deliver consistent financial growth to help establish Chambers as one of Silicon Valley’s most respected leaders before he stepped down as CEO in 2015, but company’s stock price has never approached the peak it reached a quarter century ago.