Telco's write best practices for packet switching networks

My comment was originally prompted by the meeting minutes which
reported on the survey data showing that 100% of carriers are implementing
firewalls in their gateways. The 100% is what caught my eye. As the
topic comes up in various places, large ISPs repeatedly say they are
unable to implement filters or packet screening on their high-speed
links such as at peering points. So the self-reported 100% implementation
of screening and filtering firewalls at gateways didn't seem to jive
with my understanding of the limitations faced by large ISPs.


Firewalls can be a useful tool in the security engineer's toolbox. But
they get misused a lot. I don't believe security engineers are better
programmers. If there was a class of programmers in the world that didn't
make mistakes, I would hire them to write the applications. When the
firewall is more complex than the application server it is "protecting"
which is likely to have more mistakes?

Yes and no. I don't think that security programmers are any better
than application programmers. But they might be trained differently.
For example, I suspect that most application programmers have never
heard of format string vulnerabilities. I would hope that most
security professionals have.

But you're absolutely right about the complexity of many of today's
firewalls -- I've been complaining about that for years.

    --Steve Bellovin, error
    Full text of "Firewalls" book now at