OT: ISPs: Linux's role nowadays

[Marcel Rieux]

I was under the impression that, at most small ISPs, Linux had
replaced Unix and played a central role in making things work. But
today, I spoke to an ISP employee who told me that Linux was only used
for Web servers and that, for routing and firewalling, nobody escaped
companies Cisco and Juniper which provide "solutions" where part of
the software has been integrated into hardware for efficiency
purposes.

Is this correct? Are there more explanations you can provide to make
the picture clearer?

Thanks!