Re: Why not have firewall rules by default?
William Twomey wrote:
It's my understanding (and experience) that a Debian system by default
is vulnerable to SYN flooding (at least when running services) and
other such mischeif. I was curious as to why tcp_syncookies (and
similar things) are not enabled by default.
Sorry forgot that.
Submitted by admin <http://www.linuxinsight.com/user/1> on Thu,
2006-06-29 23:12.
Send out syncookies when the syn backlog queue of a socket overflows.
This is to prevent against the common "syn flood attack". Disabled (0)
by default.
Note, that syncookies is fallback facility. It must not be used to help
highly loaded servers to stand against legal connection rate. If you see
synflood warnings in your logs, but investigation shows that they occur
because of overload with legal connections, you should tune another
parameters until this warning disappear. See: tcp_max_syn_backlog
<http://www.linuxinsight.com/proc_sys_net_ipv4_tcp_max_syn_backlog.html>,
tcp_synack_retries
<http://www.linuxinsight.com/proc_sys_net_ipv4_tcp_synack_retries.html>,
tcp_abort_on_overflow
<http://www.linuxinsight.com/proc_sys_net_ipv4_tcp_abort_on_overflow.html>.
syncookies seriously violate TCP protocol, do not allow to use TCP
extensions, can result in serious degradation of some services (for
example SMTP relaying), visible not by you, but your clients and relays,
contacting you. While you see synflood warnings in logs not being really
flooded, your server is seriously misconfigured.
Regards, Riku
Many distros (RPM-based mostly from my experience) ask you during the
install if you'd like to enable firewall protection. I was curious if
debian was every going to have this as an option?
One solution could be to have a folder called /etc/security/iptables
that contains files that get passed to iptables at startup (in the
same way /etc/rc2.d gets read in numeric order). So you could have
files like 22ssh, 23ftp, etc. with iptable rules in each file. You
could also have an 'ENABLED' variable like some files in /etc/default
have (so that ports wouldn't be opened by default; the user would have
to manually enable them for the port to be opened).
Then they'd just run /etc/init.d/iptables restart and the port would
be opened (flush the rules, reapply).
Even a central iptables-save format file that gets passed to iptables
at startup would be nice. It's easy enough to do manually, but would
be nice to see integrated with debian itself (packages managing their
own rules, etc.).
Is debian every going to introduce a better way of having iptables
rules be run at startup and easily saved/managed, or will this always
be a manual process?
Thanks!
-Will
Reply to: