Please occasionally check the Changelog at the bottom of this post to see if there have been corrections/additions since you last were here.
Over the years, I've accumulated suggestions from dozens of folks here. I made notes in my personal Tips-n-Tricks list, but it was only in February of this year that I started making a list of the "Rules" we all had established here. I intend to continue to maintain this list, so if you see one that's inaccurate or imprecise, please post in this thread or send me a PM.
The Zeroeth Rule:
Start with a hostname that is a unique (not used for anything else) FQDN resolvable in public DNS to your public IP. If you didn't do that, use slickone27's trick to get CAs, certificates, hostname entries, etc. all aligned; it will save you hours and frustration.Rule #1:
Always check the logs! For example, when you disabled Intrusion Prevention, you only disabled Snort - you did not disable the items on the other tabs! (Many people are tripped up by UDP Flood Protection which is logged in the Intrusion Prevention log file. This is often the cause of bad voice-quality with VoIP and unreliable IPsec connections that don't terminate on the UTM.)
Whenever something seems strange, always check the Intrusion Prevention, Application Control and Firewall logs. If 'Advanced Threat Protection' on the Dashboard is not zero, check that log also. Hint: If this didn't help, you likely have a routing problem. In that case, check #3 through #5.Rule #2:
Do you wonder why traffic is allowed through even when you have an explicit firewall rule blocking it? In general, a packet arriving at an interface is handled only by one of the below, in order (see images at the bottom):
What happens with outbound traffic?
Before the packet leaves, ATP will block it if the destination is on a list of malicious IPs.
Never create a Host/Network definition bound to a specific interface. Always leave all definitions with 'Interface: <<Any>>'.
There are two known exceptions
Rule #3.1: Other solutions to routing problems (not seeing any blocks, but not getting responses) include:
When creating DNATs for traffic arriving from the internet, in "Going to:" always use the "(Address)" object created by WebAdmin when the interface or the Additional Address was defined. For any Traffic Selector to apply to packets with a destination of an IP on the UTM, the corresponding "(Address)" object must be used. Under the covers, it's iptables that does the work. Using "Any" or a normal Network/Host definition causes the Traffic Selector to apply to packets in the FORWARD chain. The "(Address)" objects are bound to the interface on which they're defined, so that causes the Selector to apply to the INPUT chain.
In NAT rules, it is a good habit to leave a field blank when not making a change. In the case of a service with a single destination port, this makes no difference. In the case of a service with multiple ports, or a Group, repeating the service makes the NAT rule ineffective.
There are only six reasons to sync users from AD to the ASG/UTM:
There's no other reason to sync users to WebAdmin - certainly not for AD-SSO.
If you have slow throughput and/or ifconfig shows errors, collisions, etc., try these steps, in sequence, until your problem goes away:
Before changing the hardware the UTM runs on, go to 'Interfaces & Routing >> Interfaces' and, on the 'Hardware' tab, edit each NIC to have a 'Virtual MAC Address' that copies the existing MAC. This will cause your new NICs to be recognized immediately after the configuration is restored. The alternative is to make certain that each router/switch connected to the various NICs has cleared its ARP table:
When a Web Filtering Filter Action changes based on Policies with Time Events, established connections like YouTube will continue to function and will not be blocked. Use Sheldon's Trick: create a firewall Block rule for a one-minute Time Event after your policy allowing traffic is deactivated by a Time Event and one blocking traffic then handles the requests.
Cheers - Bob
Changelog: 2021-02-16 Expanded #2.1 based on a question posed by usec-dz; 2020-11-12 Based on a comment by Shaun Raven , I clarified the warning about SMTP Transparent in #2. 2019-04-17 Added the information about ATP to #2.1 after stu asked a question about it; 2019-01-02 Added exception for Uplink Balancing to #3 as suggested by Toni LuCar; 2018-12-30 Deleted reference to encryption/signing from Toni LuCar; #6 based on a comment from2018-12-28 Added #2.1 based on a question from member Davis Admin; 2018-01-03 Added a line to #3 based on a post by shaun threetwotwosix; 2017-12-27 apijnappels posted this suggestion for the * on #2.5; 2017-12-09 In #2, inserted #3 about ICMP; 2017-06-09 Replaced the flow diagram mentioned in #2 with a newer version and then put the old one back along with an older iptables version, too; 2017-05-30 In #2, - moved DNATs from #3 to #4 (after Intrusion Prevention) - I think that's right; 2017-05-20 Added the question at the top of #2 based on a suggestion from Louis-M; 2017-04-02 Reformatted #2 based on an idea from Louis-M; 2017-02-16 Changed #1 because people were ignoring notes and parenthetical remarks. Two people today ignored my notes and -omments, turned off IPS and thought they were following the rule!; 2017-01-25 added Intrusion Prevention to #2; 2017-01-16 added parenthetical remark in #3.1 based on a comment by new member Brendan Corcoran; 2016-12-08 added #9; 2016-12-03 added by a new member; iptables information to #4 because of a question asked by new member Len Goddard; 2016-10-22 added comments to the end of NOTE on #1 and updated #3 with the exception noted by vilic in March; 2016-10-18 added NOTE to #1; 2016-05-06 added the parenthetical remark about the Transparent-mode SMTP Proxy -to #2 thanks to a report by fellow member Matthew; 2015-10-05 added hint to #1; 2015-09-25 typo; 2015-08-13 Changed #7 to numbering instead of bullet points; 2015-07-10 Bart van Kampen's tests proved that AppCtrl comes after firewall rules, so -#2 was modified; 2015-06-19 Thanks to new member jleigh5, added second line to #6 about User Portal; 2015-06-14 "unique..." added to 0-eth rule; 2015-06-11 added details on Intel NICs based on a comment from William; 2015-06-07 changed the link in #0 to work with Macs; 2015-05-25 added the first reason in #6 about WebAdmin; 2015-04-10 added link to feature request in #6; 2015-03-15 clearer wording in Zeroeth; 2015-02-03 #8 thanks to BarryG and AppCtrl in #2 thanks to FrankBarmentlo; 2014-12-24 added Country Blocking in #2; 2014-09-10 added conntrack in #2; 2014-09-09 added Advanced Threat in #1; 2013-06-10 added BarryG's masq idea in 3.1; 2013-06-08 added fourth reason to #6
Excellent rules Grandis Professorem of the Sophos UTM! Thank you Bob. With over 15,000 posts, there is no doubt that you are the man!
Simon, if someone doesn't follow the Zeroeth rule, it complicates configuration for most VPNs and email, necessitating work-arounds that make it difficult for someone else to help or follow as a new admin.
Cheers - Bob