In message <[email protected]>, "Ronald F. Guilmette" writes: > > In message <[email protected]>, > Ian Smith <[email protected]> wrote: > > >As assorted experts have suggested, you need a stateful rule. It's > >really not that hard; if you _only_ needed to protect ntp on udp: > > > > kldload ipfw && add 65000 allow ip from any to any # load null fw > > ipfw add allow udp from me to any ntp out xmit $outsideif keep-state > > ipfw add deny udp from any to me ntp in recv $outsideif > > > >Done. Perfectly configured for this one purpose, statefully no less .. > > Sounds great to me! However I've never really used any of the stateful > ipfw stuff, so I'm venturing out into what, for me, are unfamiliar waters. > So I hope you'll be kind and entertain a question or two, to help me > understand exactly what I'm supposed to do. > > I've just skimmed over the page here: > > https://www.freebsd.org/doc/handbook/firewalls-ipfw.html > > and my questions are based on the tutorial information I've found there. > > First question: In addition to what you have written above, may I safely > assume that I also need an additional rule, somewhere early in my entire > (numbered) list of rules, that just simply says "check-state"? > > Second question: In the example text given just about half-way down on > the web page cited above, within part of a big block of example rules I > see this: > > # Allow outbound NTP > $cmd 00260 allow tcp from any to any 37 out via $pif setup keep-state > > This is more than a little befuddling to me, for one simple reason... I had > no idea until now that NTP could even make use of TCP, rather than, or in > addition to UDP. But I did look in my /etc/services file and saw this: > > ntp 123/tcp #Network Time Protocol > ntp 123/udp #Network Time Protocol > > so obviously, yes, both UDP and TCP can be used for the NTP protocol, > rather like DNS, I gather. No. IANA (Jon) just assigned/reserved both UDP and TCP for all protocols at the time. HTTP is also listed as UDP and TCP but it is only TCP with UDP reserved. > But the example, noted above, as given > within the FreeBSD Handbook appears to make the assumption that NTP is > using TCP. That still leaves me a bit befuddled, because I had assumed... > until now... that tcpd would be doing all of its communicating strictly > via UDP. (I mean ntpd's use of UDP, rather than TCP, is _the_ essential > thing that has given rise to all of these NTP reflection attacks, no? > The IP address spoofing of the intended vctim becomes one helluva lot > harder if it has to be done within the context of TCP, rather than UDP, > yes?) > > So, um, when, if ever, does ntpd use TCP, rather than UDP, and how would > a sysadmin running ntpd tell it to use either UDP or TCP? NTP uses UDP. Period. > (My apologies if this is stuff that everybody else already knows. I sure > don't.) > > Last question: Assuming that my local ntpd is strictly and only using > UDP for all communication, would something like the following be a proper > set of additions to my current ipfw rules? > > add 00101 check-state > add 00500 pass udp from <localip> 123 to any 123 out via $pif keep-stat > e > > If not, what should I use instead? > > Thanks in advance for all help & understanding. > > > Regards, > rfg > _______________________________________________ > [email protected] mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-security > To unsubscribe, send any mail to "[email protected]" -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: [email protected] _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-security To unsubscribe, send any mail to "[email protected]"