>Date: Sun, 23 Dec 2007 06:04:02 -0800 (PST)
>From: Nash Nipples <trashy_bumper@yahoo.com>
>To: freebsd-security@freebsd.org
>Subject: Re: IPFW: Blocking me out. How to debug?
>
>Dear W.D.
>
>oh come on. i have the same problem.
Which problem are we talking about?
cut and paste problem.
>cut and paste logic:
>
>#!/bin/sh
>#1. count packets
>#2. allow everything on lo0 (loopback)
>#3. slow down and deny packets to buffer overflow enabled daemons
>#3.5 to list all the buffer overflow enabled daemons use this sockstat
-46ul>#4. allow everything in and out on the Ethernet interface fxp0.
>Remember - wires are long things!
What does this mean?
this means that instead of speaking of policies its rather more important to
keep your wires safe
>#5. switch sshd to a different port like 55 and use keys to
authenticate >#6. do ipfw show every morning
Why?
you will be surprised but moving sshd to a non-standard port will make your logs
cleaner instantly. it is really exciting to read the passwords files in your
/var/log/auth.log but this again a traffic and load issue. some people just
think its fun to abuse the sshd daemon.
so you better keep a hand on the heartbeat and maintain good backups. that's
probably a thing to practice prior to ipfw facility
>#7. do ipfw zero every evening or as often as your boss wants that
How about a cron job that sends out a report then zero's ipfw?
ofcourse you can read reports. but you will become cron dependant. and that
makes you look like a paper monkey.
plus someone will think you don't really hang on the box too often.
>#8. learn how to modify this script quickly just to plumb all the
>other things that leak
What other things?
there are always some things that u just cant predict at this very moment so you
need to make decisions and which is more important take some actions. for
example blocking out some script kiddie who's sending you a list of ftp
passwords.
>#9. you cant block yourself out if you run this script with a trailing
>'&' e.g. sh /etc/ipfw.rules &
Hmmm. I'll have to try that. Would something like this
work to reload the rules?
ipfw disable firewall; sh /etc/ipfw.rules &
just sh /etc/ipfw.rules & thats enough to survive the ipfw -f flush and
reload afterwards
>#TODO: write a program that sends bills to customers
>#BUGS: it cant smile
>
>cmd="/sbin/ipfw"
>ext1="fxp0"
>gentleports="21,25,514"
Why are these ports "gentle"?
all open ports are gentle and potentially insecure. if you are not using them
for a reason don't leave them hanging open
those 3 ports are most likely to be left open. try sockstat -46ul to list em
>
>#accounting
>#i need these figures to see how bad things are going
>$cmd 100 count ip from any to any in via lo0
>$cmd 110 count ip from any to any out via lo0
>$cmd 120 count ip from any to any in via $ext1
>
>
>
>$cmd 130 count ip from any to any out via $ext1
>
>#if counters below grow too high u are screwed
How so?
there is such thing as icmp tunnels. i don't really know how they work but i
don't want someone to dig one through my box cuz im gona have to pay for the
traffic. keeping an eye on these counters will give you a hint when something
wrong is happening.
daily report you get by cron is a security funerals
> #this counter should not vary much comparing to the next one
>$cmd 210 count icmp from any to any out via $ext1
> #if there is an obvious difference someone's digging holes in the
yard
What does this mean?
that means icmp tunnels and sanity check. you shouldn't have more pings than
tcp frames.
Im only giving you basic ideas emphasizing importance of personal experience.
the way you go from here is your own paranoid activity
> $cmd 220 count icmp from any to any in via $ext1
> #too much of dns.
>$cmd 230 count ip from any to any 53 out via $ext1
>$cmd 240 count ip from any to any 53 in via $ext1
Why too much?
because you want to remember how much of dns you had at this time yesterday and
how much of dns you see now.
you might still have a chance to bump a worm or a trojan isnt it cool? ofcourse
you can go the other way. and just say to your boss "oh i think we had a
little too much of dns last month". its okay that most of dns requests one
day were pointless
>
>#if counters below grow too high you have screwed someone else
Who? Why?
sendmail freaked out. it couldn't have resolved something and kept trying.
all night untill u get the cron report. no one's fault. traffic wasted. what
if someone was sending out spam? anywho for whatever reason.
>#oh yes. someone's got mail.
>$cmd 300 count ip from any to any 25 out via $ext1
>#which way did it go
>$cmd 310 count ip from any to any 25 via lo0
>
>#policy
>$cmd 1000 allow all from any to any via lo0
>/sbin/ipfw add 1110 pipe 1 ip from any to me $gentleports in via $ext1
>/sbin/ipfw pipe 1 config bw 1Kbit/s queue 1Kbytes
>
>$cmd 1120 deny ip from any to me $gentleports in via $ext1
>$cmd 1130 allow all from any to any via ext1
>#you will wonder but the next rule still has a match
>$cmd 1140 deny log all from any to any
What is it?
maybe i have made a few syntax mistakes but i like the idea here. allow
everything on lo0.
set up a pipe (traffic shaper routine) to the ports u are trying to protect on
$ext1. and reject on a slow link
what if there is some idiot who will just keep trying to access your syslog
daemon all night on a gigabit link?
>
>I'm sorry but i cant draw pretty pictures to make it any more obvious
thats a statement>
>Nash
>
>
>----- Original Message ----
>From: W. D. <WD@US-Webmasters.com>
>To: FreeBSD-Security@FreeBSD.org
>Cc: Ian Smith <info@plot.uz>
>Sent: Friday, December 21, 2007 9:30:11 AM
>Subject: Re: IPFW: Blocking me out. How to debug?
>
>
>At 05:45 12/20/2007, Ian Smith, wrote:
>
>Thanks for your reply Ian. This is the kind of
>information I am looking for.
>
>
>>Firstly, this really belongs over on freebsd-net@ if not
>>freebsd-questions@, but anyway ..
>
>I'll be glad to move it there if you would like. I
>figured that since IPFW/Firewalls are security
>related, that FreeBSD-Security would be the most
>appropriate place.
>
>
>>On Thu, 20 Dec 2007, W. D. wrote:
>>
>> > At 03:49 12/17/2007, Tuomo Latto wrote:
>> > >W. D. wrote:
>> > >> How do I tell which rule is blocking me out? SSH *is*
working,
>> > >> but others are not.
>> > >
>> > >It all depends on what you mean by "blocking you
out" and
> "others".
>>
>>True; it's not really clear what you're trying to do, whether
this is
> a
>>single server with a single net interface with no NAT or what, but
> based
>>on your present rules I'll have to make that assumption.
>
>OK, sorry. I guess I just assumed that it would be obvious
>that this is a Web server. ("Never assume anything, my good
>fellow" - Sherlock Holmes).
>
>By the way, it is/will be running Plesk server management
>software, if it matters:
>http://www.swsoft.com/en/products/plesk/reqs/
>
>Also, this server is on an internal LAN before I subject
>it to the wild, untamed, InterWeb, with its dangerous
>internets darting back and forth inside all of the tubes.
>
>
>> > >> # Loopback:
>> > >> # Allow anything on the local loopback:
>> > >> add allow all from any to any via lo0
>> > >> add deny ip from any to 127.0.0.0/8
>> > >> add deny ip from 127.0.0.0/8 to any
>>
>>Meaning, these rules are ok and not the problem. Ignore Mr. Nipples.
>
>With a name like that, it's hard to take him seriously. ;^)
>
>
>>
>> > >> # Allow established connections:
>> > >> add allow tcp from any to any established
>>
>>That's ok. It may help you in debugging what's happening to
use:
>>
>> allow [log] tcp from any to any in established
>> allow [log] tcp from any to any out established
>
>I assume here that "[log]" means to insert "log" for
>debugging like this:
>
> allow log tcp from any to any in established
> allow log tcp from any to any out established
>
>rather than including the square brackets, "[" &
"]",
>correct?
>
>I have done that and have included my latest ruleset
>below.
>
>
>
>>and really, using 'any to any' without specifying on which
interfaces
> or
>>whether 'any' is your box or the outside world is a bit too
general,
> but
>>moving on ..
>
>OK. What should I do? I only plan on having one
>Ethernet interface. What would be more secure?
>
>
>
>> > >> # Deny fragmented packets:
>> > >> add deny ip from any to any frag
>
>> > >> # Show pings:
>> > >> add count icmp from any to any icmptypes 8 in
>> > >
>>
>>That's inbound ping requests. Don't forget that
'inbound' means
> coming
>>into the firewall, not necessarily from the outside world. Your own
>>ping requests _from_ this box also have to both come in, and go out.
>
>Hmmm. OK. Outbound Ping will be rarely used, but should
>be allowed. Isn't that included in the next rule?
>
>
>> > >> # Allow pings, ping replies, and host unreach:
>> > >> add allow icmp from any to any icmptypes 0,8,3
>> > >
>>
>>Add icmptype 11 as well if you want traceroutes to work ..
>>
>> > >> # Allow UDP traceroutes:
>> > >> add allow udp from any to any 33434-34458 in
>> > >> add allow udp from any 33434-34458 to any out
>> > >
>>
>>Ok, though udp rules are often better done statefully. See below.
>>
>> > >> # Allow DNS with name server
>> > >> add allow udp from any to any domain out
>> > >> add allow udp from any domain to any in
>> > >Nope.
>>
>>You want to watch out here. This allows udp packets from any address
>>with source port 53 to connect with any open udp port on your system,
>>and allows the responses as well. It's a simple matter using such
as
>>netcat to source packets from port 53.
>
>Should I restrict it by specifically stating the service?
>How can I be safe? What would the rule look like?
>
>
>>I gather from this that you're not running a DNS server yourself,
but
>>using upstream server/s? In that case a stateful rule is safer:
>
>Again, I apologize for not being clear. I will be running
>DNS on this box for the domains being hosted. So, it will
>be polled whenever a request for a hosted domain is needed.
>
>
>
>> allow udp from me to any 53 keep-state
>>
>>which allows after the return packets but denies connections not
>>initiated from your box.
>>
>> > >> # SSH
>> > >> # Note that /etc/hosts.allow has restrictions
>> > >> # on which IP addresses are allowed.
>> > >> #
>> > >> # Allow SSH:
>> > >> add allow tcp from any to any ssh in setup
>> > >
>>
>>By 'ssh working', I guess you mean ssh connections to this box
from
>>elsewhere, rather than ssh connections from this box? Not clear.
>
>Sorry! I am using SSH into this box, since it is easier to
>cut and paste for editing and configuration.
>
>I can't really see a situation where I would normally need to SSH
>outbound, can you? I use the Windoze boxes for that.
>
>
>> > >> # HTTP & HTTPS:
>> > >> add allow tcp from any to any https in setup
>> > >> add allow tcp from any to any http in setup
>> > >
>>
>>So, you have a webserver running on this box, listening on ports 80
> and
>>443? You've verified with 'netstat -finet -a' that this is
the case?
>
>Yes:
>
># netstat -finet -a
>Active Internet connections (including servers)
>Proto Recv-Q Send-Q Local Address Foreign Address
> (state)
>tcp4 0 0 192.168.1.109.ssh 192.168.1.107.3502
> ESTABLISHED
>tcp4 0 52 192.168.1.109.ssh 192.168.1.107.2266
> ESTABLISHED
>tcp4 0 0 *.poppassd *.*
> LISTEN
>tcp4 0 0 *.ftp *.*
> LISTEN
>tcp4 0 0 *.smtps *.*
> LISTEN
>tcp4 0 0 *.smtp *.*
> LISTEN
>tcp4 0 0 localhost.locald.3000 *.*
> LISTEN
>tcp4 0 0 *.pop3s *.*
> LISTEN
>tcp4 0 0 *.pop3 *.*
> LISTEN
>tcp4 0 0 *.imaps *.*
> LISTEN
>tcp4 0 0 *.imap *.*
> LISTEN
>tcp4 0 0 *.8443 *.*
> LISTEN
>tcp4 0 0 *.8880 *.*
> LISTEN
>tcp4 0 0 *.3306 *.*
> LISTEN
>tcp4 0 0 localhost.locald.8005 *.*
> LISTEN
>tcp4 0 0 *.9008 *.*
> LISTEN
>tcp4 0 0 *.8009 *.*
> LISTEN
>tcp46 0 0 *.https *.*
> LISTEN
>tcp46 0 0 *.http *.*
> LISTEN
>tcp4 0 0 *.9080 *.*
> LISTEN
>tcp4 0 0 *.8180 *.*
> LISTEN
>tcp4 0 0 localhost.locald.postg *.*
> LISTEN
>tcp4 0 0 localhost.locald.rndc *.*
> LISTEN
>tcp4 0 0 localhost.locald.domai *.*
> LISTEN
>tcp4 0 0 192.168.1.109.domain *.*
> LISTEN
>tcp4 0 0 *.ssh *.*
> LISTEN
>udp4 0 0 192.168.1.109.24889 ns1.ournameserver.net.53
>udp4 0 0 *.51750 *.*
>udp4 0 0 localhost.locald.domai *.*
>udp4 0 0 192.168.1.109.domain *.*
>udp4 0 0 *.syslog *.*
>
>
>
>
>>
>> > >> # Mail: SMTP & IMAP:
>> > >> add allow tcp from any to any smtp in setup
>> > >> add allow tcp from any to any imap in setup
>> > >
>>
>>You're running SMTP and IMAP servers, verified as above?
>>
>>You see, this also allows you (as 'any') to connect to any
outside
> SMTP
>>server too. It really helps to differentiate connections into your
> box
>>from those you're making to outside boxes, which these don't do.
>>
>>Have a close look at the 'simple' section in rc.firewall.
>
>I have scanned various versions of "rc.firewall". I kinda
understand
>what is going on, but there are so many places that seem
anti-intuitive>to me.
>
>Also, what are the differences between running a script and loading
>these rules on bootup?
>
>
>
>>There are
>>advantages to running a script such as that rather than rules in a
> file,
>>like variable substitution, at least while getting it all working
> right.
>
>I have mixed feelings about variables. I guess they make
>it easier if you change a network card or IP addresses--you
>only have to do it in one place.
>
>However, a search and replace command doesn't take much
>time at all. Also, they add a level of complexity to
>a situation that (to me) is complex enough already.
>And, I wonder if by not using variables, I can save a
>few microseconds when processing traffic. ;^)
>
>
>
>> > >> # FTP:
>> > >> add allow tcp from any to any ftp in setup
>> > >> add allow tcp from any to any ftp\-data in setup
>> > >> add allow tcp from any ftp\-data to any setup out
>> > >
>>
>>Mmm, I prefer using and enforcing FTP passive mode, but YMMV.
>
>How would I do that? This guy doesn't think it's even
>possible:
>http://tinyurl.com/2z6ynr
>
>
>> > >> # Allow NTP in and out
>> > >> add allow udp from any ntp to 128.252.19.1 ntp
out
>> > >> add allow udp from 128.252.19.1 ntp to any ntp in
>> > >
>>
>>Unless running a time service for other boxes, something like:
>>
>> allow udp from me to any ntp keep-state # or to a specific server
>
>Well, I think that since NTP is such a minimal user
>of resources, that I would like to rely on this
>box for the correct time. That way, I don't have
>to bug the stratum 1 boxes. Shall I use my original?
>
>
>>
>> > >> # Deny and log everything else:
>> > >> add deny log all from any to any
>> > >Bingo!
>>
>>Ok, so you got rid of interface 'all', great.
>
>Is this better?
>
> add deny log ip from any to any
>
>If so, I just don't understand this. Here is what the
>"Fine Manual" says:
>
> =============================================================>
protocol: [not] protocol-name | protocol-number
> An IP protocol specified by number or name (for a complete list
> see /etc/protocols), or one of the following keywords:
>
> ip4 | ipv4
> Matches IPv4 packets.
>
> ip6 | ipv6
> Matches IPv6 packets.
>
> ip | all
> Matches any packet.
> =============================================================>
>According to this, "ip" and "all" are synonymous.
Criminy!
>What am I missing here?
>
>
>
>> > >"ipfw -a list" may also help (packet counts).
>>
>>It's only a short ruleset, it may help us if you show the output of
> say
>>'ipfw -t show' (or ipfw -at list, same thing), if you're
still having
>>problems, but see below re 'inness' and 'outness'.
>>
>> > I've been banging my head against this for the past few
>> > days. I don't get it.
>> >
>> > My understanding of the way this is supposed to work is
>> > that:
>> >
>> > # HTTP & HTTPS:
>> > add allow tcp from any to any https in setup
>> > add allow tcp from any to any http in setup
>> >
>> > should let initial HTTP & HTTPS requests through,
>> > and that:
>> >
>> > # Allow established connections:
>> > add allow tcp from any to any established
>>
>>Not quite. Looks like you're allowing http/https setup packets in
> (ie,
>>into the firewall) but not letting them out (of the firewall, to the
>>webserver). For example in the 'simple' ruleset mentioned, we
have:
>>
>> # Allow access to our WWW
>> ${fwcmd} add pass tcp from any to ${oip} 80 setup
>>
>> # Reject&Log all setup of incoming connections from the
> outside
>> ${fwcmd} add deny log tcp from any to any in via ${oif} setup
>>
>> # Allow setup of any other TCP connection
>> ${fwcmd} add pass tcp from any to any setup
>
>I really don't get the above rule. Isn't it saying that
>*any* kind of TCP connection can come in or go out initially?
>
>
>
>>Note there's no 'in' or 'out' on the port 80 rule,
so this allows the
>>packets on both the in and out pass of the firewall. Also, the IP is
>>specified as our IP - 'me' will do fine if it's just this
box.
>
>In my set, should I include some "out" rules like this:
>
> add allow tcp from any to any https out setup
> add allow tcp from any to any http out setup
>
>
>>
>> > should allow connections that are "setup" to
>> > continue. Do I need a "check-state" or
"keep-state"
>> > statement somewhere?
>>
>>No, though you can use stateful TCP rules if you want to, in which
> case
>>you'll want to DENY established connections. Personally I find
> relying
>>on the TCP state established by using 'setup' and
'established' fine
> for
>>TCP, but tend to use keep-state for UDP and some ICMP rules.
>
>That sounds reasonable.
>
>
>> > I don't understand what is wrong with the last rule:
>> >
>> > # Deny and log everything else:
>> > add deny log all from any to any
>> >
>> > My understanding is that anything that doesn't match
>> > the previous rules will match this one and hence
>> > be logged and denied. Is this not correct?
>>
>>That's correct. Aren't you seeing any? Try show rather than
tell.
>
>Showing:
>
># ipfw -a -S -N -t list
>00100 688 173384 Thu Dec 20 15:32:17 2007 set 0 allow log logamount
> 10 ip from any to any via lo0
>00200 0 0 set 0 deny log logamount 10
> ip from any to 127.0.0.0/8
>00300 0 0 set 0 deny log logamount 10
> ip from 127.0.0.0/8 to any
>00400 4344 1712050 Fri Dec 21 00:23:37 2007 set 0 allow log logamount
> 10 tcp from any to any established
>00500 0 0 set 0 deny log logamount 10
> ip from any to any frag
>00600 4 240 Wed Dec 19 23:05:31 2007 set 0 count icmp from any
> to any icmptypes 8 in
>00700 8 480 Wed Dec 19 23:05:31 2007 set 0 allow log logamount
> 10 icmp from any to any icmptypes 0,3,8
>00800 0 0 set 0 allow log logamount
10> udp from any to any dst-port 33434-34458 in
>00900 0 0 set 0 allow log logamount
10> udp from any 33434-34458 to any out
>01000 366 24038 Fri Dec 21 00:02:00 2007 set 0 allow log logamount
> 10 udp from any to any dst-port domain out
>01100 364 59582 Fri Dec 21 00:02:00 2007 set 0 allow log logamount
> 10 udp from any domain to any in
>01200 1 48 Thu Dec 20 16:49:47 2007 set 0 allow log logamount
> 10 tcp from any to any dst-port ssh in setup
>01300 0 0 set 0 allow log logamount
10> tcp from any to any dst-port https in setup
>01400 6 288 Thu Dec 20 14:43:38 2007 set 0 allow log logamount
> 10 tcp from any to any dst-port http in setup
>01500 98 6272 Fri Dec 21 00:02:00 2007 set 0 allow log logamount
> 10 tcp from any to any dst-port http
>01600 1 64 Thu Dec 20 15:25:01 2007 set 0 allow log logamount
> 10 tcp from any to any dst-port https
>01700 0 0 set 0 allow log logamount
10> tcp from any to any dst-port smtp in setup
>01800 0 0 set 0 allow log logamount
10> tcp from any to any dst-port imap in setup
>01900 43 2064 Wed Dec 19 23:16:18 2007 set 0 allow log logamount
> 10 tcp from any to any dst-port ftp in setup
>02000 0 0 set 0 allow log logamount
10> tcp from any to any dst-port ftp-data in setup
>02100 0 0 set 0 allow log logamount
10> tcp from any ftp-data to any setup out
>02200 100 7600 Thu Dec 20 23:47:00 2007 set 0 allow log logamount
> 10 udp from any ntp to navobs1.wustl.edu dst-port ntp out
>02300 100 7600 Thu Dec 20 23:47:00 2007 set 0 allow log logamount
> 10 udp from navobs1.wustl.edu ntp to any dst-port ntp in
>02400 2058 226123 Fri Dec 21 00:17:20 2007 set 0 deny log logamount
10> ip from any to any
>65535 7 909 Wed Dec 19 22:58:29 2007 set 31 deny ip from any to
> any
>
>Lot of stuff being denied. I think some of that
>is my HTTP and HTTPS initial requests. What to do?
>
>>
>> > Again, I am having a great deal of difficulty
>> > understanding why these rules don't work as expected.
>> > I've scoured the 'Net and printed out just about
>> > every coherent ruleset out there.
>> >
>> > Besides adding the "log" keyword on all of the rules,
>> > these are the debugging tools I have been using:
>> >
>> > ipfw disable firewall
>> > ipfw -f flush
>> > ipfw enable firewall
>> > /etc/rc.d/ipfw start
>> > ipfw -a -S -N -t list
>> > ipfw list
>> > tail -f /var/log/ipfw/ipfw.log
>> > tcpdump -i nve0 'proto \tcp && port http'
> netstat -finet -a
>> >
>> > Could anyone please throw this tired dog a bone?
>>
>>Getting the two-pass nature of ipfw understood seems to be your main
>>difficulty.
>
>I would definitely agree with you. I am completely lost.
>
>By "two-pass" do you mean "in" to the firewall, and then
>"in" to the webserver, and another "two-pass":
"out" from the
>webserver, and "out" from the firewall?
>
>
>>I know it was for me back then. Have a look at the section
>>in ipfw(8) regarding packet flows, and although it sounds trite, RTFM
>>about 10 times :)
>>
>>Cheers, Ian
>
>Love the "Fine Manual" --not! Just not enough examples for
>me to understand everything. Too much abstraction--AAArrrrgh!
>
>Am using this link, since "man ipfw" doesn't work on 6.2. (I
dare
>someone to explain to me how to get it to work):
>http://www.freebsd.org/cgi/man.cgi?query=ipfw&sektion=8
>
>Thanks for your help, Ian. Would appreciate it if you would
>kick my butt in the proper direction again.
>
>Any other takers/kickers?
>
>
>Latest grope in the dark:
>==============================================================>#
ipfw.rules
># ipfw firewall ruleset
># 2007 Dec 20
>
># By default, everything is denied access. You
># need to specifically allow something for it
># to work.
>
># Loopback:
># Allow anything on the local loopback:
>add allow log all from any to any via lo0
>
># Disallow spoofed access to local:
>add deny log ip from any to 127.0.0.0/8
>add deny log ip from 127.0.0.0/8 to any
>
># Allow established connections:
>add allow log tcp from any to any established
>
># Deny fragmented packets:
>add deny log ip from any to any frag
>
># Show pings:
>add count icmp from any to any icmptypes 8 in
>
># Allow pings, ping replies, and host unreach:
>add allow log icmp from any to any icmptypes 0,8,3
>
># Allow UDP traceroutes:
>add allow log udp from any to any 33434-34458 in
>add allow log udp from any 33434-34458 to any out
>
># Allow DNS with name server
>add allow log udp from any to any domain out
>add allow log udp from any domain to any in
>
># SSH
># Note that /etc/hosts.allow has restrictions
># on which IP addresses are allowed.
>#
># Allow SSH:
>add allow log tcp from any to any ssh in setup
>
># HTTP & HTTPS:
>add allow log tcp from any to any https in setup
>add allow log tcp from any to any http in setup
>
>add allow log tcp from any to any dst-port 80
>add allow log tcp from any to any dst-port 443
>
># Mail: SMTP & IMAP:
>add allow log tcp from any to any smtp in setup
>add allow log tcp from any to any imap in setup
>
># FTP:
>add allow log tcp from any to any ftp in setup
>add allow log tcp from any to any ftp\-data in setup
>add allow log tcp from any ftp\-data to any setup out
>
># Allow NTP in and out
>add allow log udp from any ntp to 128.252.19.1 ntp out
>add allow log udp from 128.252.19.1 ntp to any ntp in
>
>
># Deny and log everything else:
># add deny log all from any to any
>add deny log ip from any to any
>==============================================================>
>
>
>
>
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