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Sophos Firewall: Understanding New decoupled NAT and firewall changes in v18

PMParth

Disclaimer: This information is provided as-is for the benefit of the Community. Please contact Sophos Professional Services if you require assistance with your specific environment.

Hi,

Based on the discussion and queries we have observed on various threads, here is the things to know about new decoupled NAT and firewall changes in v18.

Update - This in-depth video has been produced to help explain the new NAT changes in SFOS v18: https://player.vimeo.com/video/376241042 

1) What is changed related to NAT in Sophos firewall v18? What is Decoupled NAT? Why we changed?

with v18, Sophos Firewall has moved towards more standardized NAT design in which network translation configuration is now decoupled from firewalling configuration for better manageability in the larger sized deployments.

Starting Sophos firewall v18, NAT is now a separate rule table that will be traversed from top to bottom prioritized rule set for network translation decisions. The configuration offers better flexibility, manageability with less number of NAT & firewall rules. With v18, Sophos Firewall’s enterprise NAT capability is now at par with other competitive players.

The new design offers ease of configuration and management for all NAT capabilities:

  • Admin can configure Source translation, Destination translation or Full NAT translation in one NAT rule.
  • Admin can now create loopback (hair pinning) and reflexive NAT rule with One-Click UI options; created loopback and reflexive rule will be now visible on NAT table UI
  • Many to Many, One to Many, Many to one like load balance scenario and redundant network translations are now easy to configure in the same NAT rule with load balancing and health check methods.
  • admin can now configure NAT rule matching based on In and Out Interface as an added granular matching criteria.

Based on what we have been hearing from our customers, v18 now removes confusing business application firewall rule type existing in v17.x and earlier. destination NAT capability of the biz apps rule has been folded into the same NAT rule. Single firewall rule type can now achieve WAF (as a part of action) and other security configurations.

For customers who don't want to manage a separate NAT rule table, Sophos firewall v18 offers a differentiating LinkedNAT functionality - refer LinkedNAT specific FAQs for details.

 

2) I am running v17.x; will there be any impact/ behavior change on my existing deployment (specific to NAT) if I upgrade to v18?

No. We have implemented the migration in such a way that it will automatically migrate v17.x NAT configuration (integrated into firewall rule) to v18 NAT configurations. You need not to take any manual steps.

When you migrate from v17.x to v18, you would see many LinkedNAT rules already created – many of them could be with similar source NAT translation, for example – many rules with MASQ as source translation. We cannot consolidate/ optimize the same automatically during migration as there could be deployments with firewall rules on v17.x without any NAT configured. You can decide to manually optimize the NAT table by creating single source translation NAT rule that takes care of translating source for multiple firewall rules, for example - single MASQ rule at the bottom of the NAT table. And you can delete multiple LinkedNAT rule created during migration.

 

3) After upgrading to v18, I see many LinkedNAT rule created on the NAT rule table. Is this normal? Can you not optimize this further in the migration?

We have implemented the migration in such a way that it will automatically migrate v17.x NAT configuration (integrated into firewall rule) to v18 NAT configurations. You need not to take any manual steps.

When you migrate from v17.x to v18, you would see many LinkedNAT rules already created – many of them could be with similar source NAT translation, for example – many rules with MASQ as source translation. We cannot consolidate/ optimize the same automatically during migration as there could be deployments with firewall rules on v17.x without any NAT configured. You can decide to manually optimize the NAT table by creating single source translation NAT rule that takes care of translating source for multiple firewall rules, for example - single MASQ rule at the bottom of the NAT table. And you can delete multiple LinkedNAT rule created during migration.

 

4) After upgrading to v18, I see a non-editable checkbox on migrated firewall rules that says "Do not apply this migrated rule to system-destined traffic". Why it is there?

This is to retain the rule matching behavior of v17.x even though we have removed Business application rule type.

In SFOS 17.x and earlier, although business application rules and user-network rules were listed in a single rule table, Sophos Firewall evaluated these rule types independently to find matching criteria. For system-destined traffic (example: accessing Sophos Firewall services) and incoming traffic (example: to internal servers) that matches a destination NAT business application rule, it ignored user-network rules and matched the traffic with business application rules.

From v18, Sophos Firewall has removed the distinction between business application and user-network rules. It now offers both as firewall rules. To ensure that the consolidation does not affect the rule-matching behavior of earlier versions, it will continue to ignore migrated user-network rules positioned above migrated business application rules for system-destined traffic and incoming traffic.

This is a read-only checkbox in the firewall rule that tells system to retain rule matching behavior of v17.x even after migrating onto v18.

 

5) I am creating a firewall rule for DNAT (destination translation) rule. Why should I configure Dst Zone match in firewall rule as (mostly) local zone (LAN/ DMZ). And, why should I configure Dst network match in firewall rule as original Dst IP (WAN IP on Sophos Firewall)?

When you create firewall rule for NAT rule in which destination is translated, you would match Dst zone as the ultimate zone in which the traffic would terminate (that is local zone – DMZ or LAN). However, you would (want to) match against the original destination IP (WAN IP on Sophos Firewall), here’s why:

  1. Usually one public IP would translate to different internal server IPs based on services. Admins can have one firewall access rule matching public IP; And NAT can take care of translating to different servers.
  2. Also, when admins add new servers in network, they need not to again modify firewall rule. With how this is implemented now – we can just edit NAT rule and we are good to go. This is true decoupled NAT/ Enterprise NAT power.
  3. Existing behavior makes it easier to configure in 1-to-Many DNAT scenario in which 1 public IP is translated against multiple local IPs. Match on the public IP adds flexibility.
  4. v18 implements more standard and industry common NAT design. With v18, Sophos Firewall’s enterprise NAT capability and configuration flow is now at par with other competitive players.

 

6) What is LinkedNAT?

With v18, Sophos firewall has moved towards more standardized NAT design in which network translation configuration is now decoupled from firewalling configuration for better manageability in the larger sized deployments.

However, For customers who don't want to manage a separate NAT rule table, Sophos firewall v18 offers a differentiating LinkedNAT feature to grandfather existing customers over to the new design in the long run. The linkedNAT feature is fundamentally designed to provide inline source NAT rule creation from firewall rule. Matching criteria for the LinkedNAT rule is linked with the respective firewall rule, admin only needs to configure or edit the Src translation decision in the LinkedNAT rule.

This means LinkedNAT rule will only be applied to the traffic matching that specific firewall rule. However, if standard NAT rules are placed before the linkedNAT rule that match the traffic, the matching NAT rule would apply. That means, LinkedNAT does NOT guarantee that it will be matched for respective firewall rule traffic (if admin creates standard NAT rule before LinkedNAT). NAT rule table will always be matched from top to bottom priority order. There is no special or reserved priority in execution for LinkedNAT rule.

LinkedNAT rule is only possible for SNAT (source translation) configuration, not for Destination translation (DNAT).

 

7) Is it mandatory to use LinkedNAT? Where should I use LinkedNAT?

It is not mandatory to use LinkedNAT. With v18, Sophos firewall has moved towards more standardized NAT design in which network translation configuration is now decoupled from firewalling configuration for better manageability.

If you have a small scale deployment (small set of firewall rules) and you don't want to manage a separate NAT rule table, you can create LinkedNAT directly from the firewall rule and ONLY configure Src translation decision while matching criteria are automatically linked with the respective firewall rule.

If you have to differentiate SNAT configuration based on Users or Schedules criteria, LinkedNAT rule becomes mandatory there. However, such configuration need is very rare, we have NOT observed such configuration in practical deployments. Also, LinkedNAT rule is only possible for SNAT (source translation) configuration, not for Destination translation (DNAT).

 

8) What is the new disabled “Drop ALL” rule at the bottom of the firewall rule table?

The default drop rule provides visual indication to user / admin that if none of the firewall rule gets match, traffic will be dropped.

You reported about two specific challenges that admin faces in v17.x.

  1. New admins are confused about the default behavior on firewall rule table – that is the behavior when no rule matches. The new disabled Drop ALL non-editable rule is a step to resolve this.
  2. Logviewer should show traffic being dropped by the default-drop behavior of firewall rule table – this is planned to be released post v18.

Currently, the logs that you see with firewall rule id ‘0’ are NOT for the traffic dropped by Drop ALL rule. In later EAP releases, we would replace them with “N/A” as those are for the traffic dropped before the firewall rule matches – for example – invalid traffic. And actual logs for traffic dropped by Drop ALL default behavior will be available in the release post v18. Meanwhile – as a workaround, one can add a drop rule at the bottom to log the dropped traffic not matched by any other firewall rule.

 

9) Do I have any demo/ training on how to configure various NAT in the new design?

To help you evaluate Sophos firewall v18 better in this early access program, here is the interactive training/ work through course - video along with the PDF handout and speaker notes. Here is the interactive course to work through Sophos Firewall v18.0:

https://community.sophos.com/products/xg-firewall/sfos-eap/sfos-v18-early-access-program/f/recommended-reads/115874/interactive-training-course-on-xg-firewall-v18-0

 

Sincerely,

Your Sophos Sophos Firewall Product Team



Updated Title
[edited by: Erick Jan at 2:01 AM (GMT -7) on 4 May 2023]
  • 0

    Thanks for the article. So more or less nat and firewall layouts will remain the same in v18 GA?

  • +1 in reply to lferrara

    Let me try to put some experience I had during these days. The goal was migrating 27 DNAT rules from another Firewall to XG v18. Since it is a DR site and no disasters were "planned" for the testing time, I dediced to share with 5 guys the project of migrating the DNAT configuration from the current product to XG v18. I did not tell them how to create the DNAT. Since Sophos is "security made simple" I told them: lets migrate the rules you have on XXX to v18 but without using online help, documentation, only with your experience and Sophos XG v18 interface.

    • All the DNAT were documented on an Excel files (source zone, listener interface/ips, destination zone, destination internal server).
    • XG installed by using 3 NICs: internal, wan1 and wan2. All IPs used were different from the current XXX ip addresses scheme
    • Creation of internal server. Since here no issue for the 5 guys. They have 3 years of experience on XXX and Cisco CCNA certified
    • Creation firewall rule. None of the 27 firewall rules were correct. None.
    • NAT? How does the NAT works here on XG v18?
    • What is linked NAT?
    • How can NAT source service to multipe WAN IPs?

    Then, I decided to show them v17 interface from a customer site. Apart some questions regarding NAT, the Wizard helped them to understand how to create the rule and they did it correctly on v17 environment (it was a test on a production installation, so the rule was disabled and deleted afterwards)

    Back to v18, they tried again: still wrong. Then I showed them the Sophos v18 training course.pdf and they said "no way, really?" At the end, in the firewall rul:

    • Destination zone: they putted LAN
    • Destination network: here the problem comes. Here they putted the list of servers or the single server where the internal service run
    • Service: some of them putted the internal service and some the external service (in the cases where the external service port was different from the internal)

    On the NAT, what the guys have done:

    • Source: Any
    • Original destination: confused. Some putte WAN port, some the WAN ip addresses, some the internal server ip
    • Original service: all agreed with the external service
    • Translated source: and now what we put here? Confused! Maybe here WAN Ip address goes here
    • Translated destination: all agreed with the internal server ip
    • Translated service: all agreed with interna service
    • Inbound interface: WAN and WAN1 (where required)
    • Outbound Interface: LAN

    This is the test I conducted with the help of 5 guys. Thanks to them. So my considerations are:

    Firewall section:

    • Consider to bring back Wizard as used in v17. In your pdf and training course, , WAF is not even documented. Now WAF is an action like allow, deny, block. Since the history of first firewalls, actions are considered 3 and not more. 
    • Wizard option was really appreciated from Sophos Community and Sophos Partners. Thanks to Community, I have contact with some Sophos Gold Partner and they do not like the absence of Wizard. They are scared to reply as the reply will be deleted or their answer will have some reflection on their business.
    • Wizard was a nice idea since the ISA Server age. I used and appreciated a lot Wizard on Microsoft and then on XG. Well done for the Wizard, nice feature.
    • Creating DNAT is a pain now. The problem are the destination network and nomenclatures. You need to put the pre-nat section in one line and post-nat section in another line. My suggestion for source are:
      • Source zone
      • Source network
      • Source service
      • Listener: here you put the ports or the WAN ip addresses.
    • For destination and services:
      • Destination zone: LAN or DMZ or whatever
      • and destination service: here the pre-nat service
    • For NAT tab:
      • Put in one line: Original Source, listeners or pre-nat ip, original service
      • Put in a second line: Translated source, destination ip, translated service

    Names you used are just confusing. Listeners are much better that what you use at the moment. Decoupling NAT and Firewall rules is a nice feature and idea, but better names and wizard can reduce confusion and ticketing to Sophos.

    Other improvements:

    • Remove the linked NAT. One the user has putted source, destination, services and so foth, before the Web protection section, a NAT button that says something like:
      • This rule matches the NAT rule id. If you leave the mouse on it, the button gives you details of the NAT rules in the next tab. From here, users can be allowed to edit the NAT and a message should say, if you edit this NAT, other firewall rules are impacted or these firewall rules are impacted. Do you want to continue.
      • NAT icon for DNAT. Once all source and destination filtered are filled, the NAT icon will tell you how the firewall rule will be translated too.
    • Bring back the Firewall icons. Use different icons for WAF, DNAT, Firewall rules and Users firewall rules.
    • If the firewall rule has no linked NAT, the NAT icon is greyed out, so it seems no NAT is matching. This should occur only if no NAT rules are matching the firewall rule. Like in this case:

    The firewall rule works as the last nat catches the traffic. NAT icon should be coloured.

    I will take a sceenshot of my reply. Just in case the reply is deleted.

  • 0

    PMParth said:

    For customers who don't want to manage a separate NAT rule table, XG firewall v18 offers a differentiating LinkedNAT functionality - refer LinkedNAT specific FAQs for details.

    I forgot...for customers: which customers? I did not find anyone on community that is happy with the new NAT table and Firewall rule. Decoupling is ok but what we are complaining is how you put menu, options together.

  • 0 in reply to lferrara

    That is elaborated beyond a professional level ... Clean.  Straightforward.

    Paul Jr

  • 0 in reply to lferrara

    Hello Luk,

    I have to take off my hat before you, I wouldn't have so much patience to prepare such a test. However, I think the result of your test is indicative of the "quality" of implementing NAT rules in v18 EAP1. At the first moment (when I saw the DNAT rule after migration from v17.5 MR8) I did not believe what I saw. If you have practical experience in configuring firewall and NAT rules, then you are not able to understand it and the only result is a pleasing back pain from the endless shaking of your head ...

    However, PMParth tries to tell us that in this way all comparable firewall manufacturers implement NAT rules.

    I can assure him that, as the DNAT is implemented in v18 EAP1, it certainly does not implement it by comparable firewall manufacturers. Just look for "How to setup in Fort*gate DNAT rule" and what a surprise, the implementation of DNAT rules is exactly the same as in UTM v9. Yes, they use something called virtual IP address for this purpose, but again the function of this object is very logical at first sight. And then they use this object in a classic DNAT rule. Who is interested can check it here

    https: //docs.fort*net.com/document/fort*gate/6.0.0/cookbook/186598/port-forwarding

    I could also shake my head after reading the following sentence: "The configuration offers better flexibility, manageability with fewer NAT and firewall rules."
    I probably live in another space-time, because so many NAT rules I have never needed in v17.5 as I need now. While in v17.5 I needed a few DNAT rules and I solved most of the Internet traffic using several MASQ rules, now I count the NAT rules to tens! And I have replaced some linked rules with MASQ rules.

    Why is Sophos still trying to convince me of something that's not true?!

    Regards

    alda

  • 0 in reply to alda

    Alda,

    I know even that product since 2005. Sophos UTM9 has some unique features and UI designed that no one on the market can compete...The Firewall creation wizard introducted on XG is a nice and well accepted feature and reflect the "security made simple" concept. As I wrote, remember we ISA Server 2000. Publishing OWA, FTP, HTTP/S was very simple and straight-forward. No one is using that old method to publish servers anymore (expect for XG v17 and XG v16). II even used the "Client Certificate authentication" mechanism...

    Anyway, let's keep focused on XG and the thread clean. We are here to give feedbacks to Sophos. I had the time to spent 4 hours with a customer where I have strong relationship. This was a personal test to understand if I am too old for understand new technology or maybe something needs to be revisited from Sophos side.

    Keep posting, Alda. If you can provide real feedback as I did, this will help to improve the product and community.

    Thanks

  • 0

    Landed here after finishing my derivatives calculation with the help of derivative tool. Thanks for this information. It is useful

    derivative tool

  • 0 in reply to alda

    I'm with Alda here Luk.  Hats off to you for 1. coming back and 2. taking the time to even do this.  

    I spent a little bit of time with v18 testing and just reverted as I was so thoroughly disappointed...I just had to shut it down.  I feel like all this time waiting has been for nothing when we could have been moving to other solutions (we have been waiting since 2017 for this...really).  How this Firewall/NAT UI even passed an internal UAT is beyond me.  Reading the justifications now just seems like a lost cause.

    At least with v15 they quickly realized that the icons in place of an actual name was silly and changed it.  I just hope that Sophos comes to their senses and admits that this design just isn't "simple" and beyond intuitive and modifies it in time for a v18 GA.

  • 0 in reply to axsom1

    axsom1 said:
    How this Firewall/NAT UI even passed an internal UAT is beyond me.  Reading the justifications now just seems like a lost cause.

    I  am with you. If people like us or with years of experience in the field, would never accept a layout like this.

    It is still a beta and I really hope that someone will reply with a :”thanks for your input, we will review the nat and firewall layouts before ga “

    If it is not the case, we will take our decisions. V18 was promised as the revolution but here we are complaining about bases things like ABC. I do not want even mentioning reports and logging as we need to keep clean this topic. To Sophos: I am interested into participating  into the SDLC,  UAT and collaborate somehow with Sophos. Feel free to reach me via email or phone.

    Regards

  • 0 in reply to lferrara

    Hello Sophos,

    I agree with Luk. I think many interesting features are implemented in v18 EAP1, such as DPI engine, SSL / TLS rules, Kerberos, DKIM, etc. However, each administrator configures these features in a second sequence only after configuring basic security features such as firewall rules and NAT. And here you can (must) always get the most points. This is the daily work of the administrator. Here the administrator cannot fumble and think "what did the developer mean when he implemented it that way?" Then a very poor implementation of these basic security features will not save even the first post of this thread. If the implementation is very well done, no such post is needed at all. Everyone will subconsciously say "of course, otherwise than in this way it is not even configurable". I think you have largely succeeded in implementing the firewall rules in v17.5, but at least as far as the links between the firewall rule and the NAT rule are concerned.
    Please be inspired by what you have at home. Please overcome the pride in yourself that you know best how it should be implemented. Because simplicity is beauty. Astaro had the implementation of NAT rules so simply implemented that at first glance, everyone understood. Please take this implementation of NAT rules, change it to XG GUI, add interface matching criteria and you will be surprised by the result. Use the drop-down list in the NAT rule section of the firewall rule to create NAT rules as needed or select from existing NAT rules. I think there is no need to think of anything else, new and avangard.
    Certainly others will add their possibly different view of how the NAT rules should be reworked. But surely everyone agrees that implementing NAT rules is unusable. At least I did not record a single positive statement on the current implementation of NAT rules.

    Yes, there is still a problem with logging and log management, but I am not so naive and I understand that it is still a long run. So hopefully we will see it in the version v18.5.

    Regards

    alda

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