Re: Discarding inbound ICMP REDIRECT by default

> I propose that we start dropping inbound ICMP REDIRECTs by default, by
> setting the net.inet.icmp.drop_redirect sysctl to 1 by default (and
> changing the associated rc.conf machinery). I've opened a Phabricator
> review at https://reviews.freebsd.org/D45102.

I propse that we NOT do this.  If you need this to protect your end
node your probably doing something really unsafe network wise.  The
place that ICMP REDIRECTS should be dropped, and is most places, is
at access routers and firewalls.

Any one that needs this change to protect there network has larger
issues than an ICMP REDIECT causing some issues.

ICMP redirectr are very usefull for not having to run routing
protocols on all your end nodes and allowing your edge/access
routers tell your internal hosts via redirects how to get to
places more efficiently.

> 
> ICMP REDIRECTs served a useful purpose in earlier networks, but on
They still serve this very usefull purpose.

> balance are more likely to represent a security issue today than to
> provide a routing benefit. With the change in review it is of course
> still possible to enable them if desired for a given installation.
> This change would appear in FreeBSD 15.0 and would not be MFC'd.
> 
> One question raised in the review is about switching the default to
> YES but keeping the special handling for "auto" (dropping ICMP
> REDIRECT if a routing daemon is in use, honouring them if not). I
> don't think this is particularly valuable given that auto was
> introduced to override the default NO when necessary; there's no need
> for it with the default being YES. That functionality could be
> maintained if there is a compelling use case, though.

The policy that is there now is exactly how things should be configured
for a host in a network protected by a proper router w/firewall.
The existing "auto" does exactly the right thing.

> 
> If you have any questions or feedback please follow up here or in the review.
> 
> 

-- 
Rod Grimes                                                 rgrimes@freebsd.org