Nameserver

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Nameserver configuration on the UTM

Last adaptation to the version: 12.6.1

New:

• Layout adjustment and port note for the mDNS-Repeater
• Updated to Redesign of the webinterface

notempty

This article refers to a Resellerpreview

v12.2.2 v11.6

Access: UTM-IP:Port or UTM-URL:Port
Port as configured at Network / Appliance Settings / Webserver
Default-Port: 11115
i.e.: https://utm.ttt-point.de:11115
Default: https://192.168.175.1:11115 Application Nameserver

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Introduction

The nameserver of the UTM offers:

• Forward zones: Name resolution (FQDN) in IP addresses
• Reverse zones: IP addresses into FQDN)
• Relay zones: Forwarding of queries belonging to a specific domain
• DNS Forwarding: Forwarding of all DNS queries

Um den Nameserver der UTM nutzen zu können, muss im Paketfilter eine Regel mit dem jeweiligen Netz als Quelle und dem Ziel  xy-Interface existieren.
Als Dienst muss mindestens  dns erlaubt werden (Port 53 für TCP und UDP).
Es empfiehlt sich in der Regel jedoch die Dienstgruppe  proxy zu verwenden. Dies gibt weitere Ports für Dienste wie z.B. den transparenten Proxy, webcache oder einen Ping frei.

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Prerequisites

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Set Firewall as Namesever

Server settings UTMuser@firewall.name.fqdnNetwork Nameserver IP The first step is to define the UTM itself as the nameserver of the firewall.

1. Configuration under Network Server settings  Area Server settings section
   DNS Server
2. Field Primary nameserver set the IP to 127.0.0.1 (localhost) as IP.
3. Save with

If no nameserver is stored, DNS queries are resolved via the root DNS servers and the DNS servers stored there for the top-level domains

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Forward-Zone

A forward zone is used to convert domain names into IP addresses.
This implementation is possible in both IPv4 (A) and IPv6 (AAAA). The following setup example shows the creation of an A-RR for a public domain.
If the DNS of the firewall is used for resolution, a private IP from the internal network should be returned.

This setting is required, among other things, if a domain whose public IP is that of the firewall is accessed from the internal network.
Without this entry, a complicated port forwarding would be required, but this way the request can be sent directly to the server without any detours.
Setup under Applications Nameserver  Area Zones Button Add forward zone.

notempty

If a NAT router is available, a forward zone must be set up.

Create A-RR

Add Forward-Zone UTMuser@firewall.name.fqdnApplicationNameserver

Step 1

Zone name: webserver.anyideas.de
Domain that is managed by an internal DNS server

Add Forward-Zone UTMuser@firewall.name.fqdnApplicationNameserver

Step 2

Nameserver Hostname: localhost
The UTM itself serves as the nameserver

Add Forward-Zone UTMuser@firewall.name.fqdnApplicationNameserver

Step 3

IP address:    

The IP address is only required if the nameserver is located in the zone that is currently being created and is not the localhost, i.e. the UTM itself

Complete the wizard with the Done button

Caption	Value	Description	Nameserver UTMuser@firewall.name.fqdnApplication Zones overview
Edit		The zone can be edited by clicking on the wrench
Settings
Type:	Normal	Setting for Forward-Zones	Edit zone UTMuser@firewall.name.fqdnApplicationNameserver Edit zone
Update:	10000 Seconds	Frequency with which the entry is updated
Retry:	1800 Seconds	Repeat update in case of failure
Expires:	3600000 Seconds	Ablauffrist des Eintrags (beginnt nach erfolgreicher Aktualisierung erneut
Minimum:	3600 Seconds
Entries
Type NS	localhost.	There is already an NS entry (with a period at the end!)
Edit		Opens the record entry for editing
Delete		Deletes the record entry
Add entry		Add another record entry
Name:	webserver.anyideas.de.	Desired domain name A dot "." is appended to the domain (=Top-Level)	Add entry UTMuser@firewall.name.fqdnApplicationNameserver Add entry
Type:	A	Select A-Record entry
Type Description NS An NS record (or NS-RR: Name Server Resource Record) is a data record of a DNS server and can fulfill two different functions: It defines which name servers are officially responsible for this zone It links zones to form a zone tree (delegation). Each zone file must contain at least one NS-RR that specifies which name server is authoritative for this zone. If, for example, the firewall itself is responsible, "localhost" must be selected/entered here. A An A-RR (A Resource Record) is used to assign an IPv4 address to a DNS name. AAAA An AAAA resource record ("quad-A") is used to assign an IPv6 address to a DNS name. This is the IPv6 equivalent of the A resource record. TXT A TXT resource record can be used to store a freely definable text in a DNS zone. TXT records can be used for tunnelling via DNS, among other things. PTR PTR resource records assign one or more host names to a given IP address in the Domain Name System. In a way, they are the counterpart to the classic assignment of one or more IP address(es) to a given host name via A or AAAA resource record. PTR Resource Records are a central element of the Reverse DNS. They are usually used exclusively in the in-addr.arpa zone (for the reverse lookup of IPv4 addresses), in the ip6.arpa zone (for the reverse lookup of IPv6 addresses)[1] and in other zones for hostnames to which a CNAME resource record from one of the aforementioned zones points. MX The MX Resource Record (MX-RR) of a domain is an entry in the Domain Name System that relates exclusively to the e-mail (SMTP) service. An MX record specifies the Fully Qualified Domain Name (FQDN) under which the mail server for a domain or subdomain can be reached. It is common to define several MX records with different priorities for a domain, so that if one mail server fails, another can receive the emails. This increases the probability that a mail can still be delivered to the recipient domain. CNAME A CNAME Resource Record (CNAME RR) is used in the Domain Name System to assign an additional name to a domain. The abbreviation "CNAME" stands for canonical name (canonical = recognized, meaning the primary, quasi real name). In the simplest case, the name of a CNAME resource record refers to the name of an A resource record and/or an AAAA resource record. The names of these resource records refer to an IP address. When changing an IP address, only a single resource record needs to be changed for several names. An NS Resource Record, MX Resource Record or PTR Resource Record must not refer to a CNAME Resource Record. Conversely, a PTR resource record may only be accessible via a CNAME resource record. The name of a CNAME resource record may not be used as the name of other resource records, as it is representative of all resource records of the target.
Value:	192.168.222.2	IP of the server to which the domain should point
		Closes the dialog for the DNS record
		Closes the dialog for editing the zone
Test A-RR
Test the created A-RR under: Network Network Tools  Area Host Settings			Network tools UTMuser@firewall.name.fqdnNetwork
Query type	A	Query type of the created DNS record
Hostname:	webserver.anyideas.de	Web server address as entered in the record entry under Name (with or without the final dot)
Nameserver:	127.0.0.1	Localhost address of the UTM
Response
If everything has been set up correctly, the domain is resolved to the correct IP address in the lower window. Alternative testing using a nslookup webserver.anyideas.de from a computer in the UTM network
Reverse-Zone Reverse DNS lookup (rDNS) refers to a DNS query in which the name is to be determined for an IP address Only PTR resource records are permitted as RR types A PTR-RR has an IP address as the request basis and a name as the result - in contrast to the A Resource Record, where a name represents the request and an IP address the result. An rDNS lookup is often used in connection with spam filters. Many spam mails are sent from fake domains. The recipient can use a reverse resolution of the IP to determine whether the domain really belongs to the incoming IP; if this is not the case, the mail is rejected. Create PTR-RR The next step is to create the PTR-RR. Here is a brief description to help you understand: As it would be extremely time-consuming to search the entire domain tree for the desired IPv4 address for an inverse request, a separate domain was created for inverse accesses, the in-addr.arpa domain. There are only three subdomain levels below this domain, so that a maximum of three steps are required to resolve an IPv4 address. The immediate subdomains of in-addr.arpa have a number between 0 and 255 as a label and represent the first component of an IPv4 address. (Example: 64.in-addr.arpa or 192.in-addr.arpa). The next level in the tree represents the second component of an IPv4 address (example: 27.64.in-addr.arpa. contains the IPv4 addresses 64.27.x.y) and the lowest level finally the third component (example: 125.27.64.in-addr.arpa contains all known IPv4 addresses of the network 64.27.125.0/24 - e.g. 64.27.125.60). As can be seen from the examples, a reverse name contains the IP address components in reverse order. This structure makes it possible to refine the reverse address space in several steps. In our following setup example, we will work with the last address space (/24). Go to Applications in the navigation bar and click on Nameserver in the drop-down menu. Click on the Add reverse zone button in the dialog that appears. In step 1, enter the desired subnet in which the IP address for the desired domain is located. Enter "localhost" under Nameserver in Step 2 and click on Done. The zone name is created automatically as described in the example above. Edit the created zone by clicking on the wrench. Click on the Add entry button in the dialog that appears. In the "Name" field, enter the last number of the host IP that belongs to the desired domain (in our example, "60"). Select "PTR" as the type. In the Value field, enter the domain to which the IP address should point. A dot "." is appended to the domain! Click on Add. Click on Save. Application Nameserver  Area Zones Button Add reverse zone
Add reverse zone UTMuser@firewall.name.fqdnApplicationNameserver Step 1 The desired subnet in which the IP address for the desired domain is located Add reverse zone UTMuser@firewall.name.fqdnApplicationNameserver Step 2 Nameserver is the localhost, i.e. the UTM itself Complete the wizard with the Done button
The newly created entry Edit and Add entry
Caption	Value	Description	Add entry UTMuser@firewall.name.fqdnApplicationNameserver Add PTR-RR entry
Name:	60	The last number block of the host IP that belongs to the desired domain (in the example 60)
Type:	PTR	PTR (Pointer)-Record
Type Description NS An NS record (or NS-RR: Name Server Resource Record) is a data record of a DNS server and can fulfill two different functions: It defines which name servers are officially responsible for this zone It links zones to form a zone tree (delegation). Each zone file must contain at least one NS-RR that specifies which name server is authoritative for this zone. If, for example, the firewall itself is responsible, "localhost" must be selected/entered here. A An A-RR (A Resource Record) is used to assign an IPv4 address to a DNS name. AAAA An AAAA resource record ("quad-A") is used to assign an IPv6 address to a DNS name. This is the IPv6 equivalent of the A resource record. TXT A TXT resource record can be used to store a freely definable text in a DNS zone. TXT records can be used for tunnelling via DNS, among other things. PTR PTR resource records assign one or more host names to a given IP address in the Domain Name System. In a way, they are the counterpart to the classic assignment of one or more IP address(es) to a given host name via A or AAAA resource record. PTR Resource Records are a central element of the Reverse DNS. They are usually used exclusively in the in-addr.arpa zone (for the reverse lookup of IPv4 addresses), in the ip6.arpa zone (for the reverse lookup of IPv6 addresses)[1] and in other zones for hostnames to which a CNAME resource record from one of the aforementioned zones points. MX The MX Resource Record (MX-RR) of a domain is an entry in the Domain Name System that relates exclusively to the e-mail (SMTP) service. An MX record specifies the Fully Qualified Domain Name (FQDN) under which the mail server for a domain or subdomain can be reached. It is common to define several MX records with different priorities for a domain, so that if one mail server fails, another can receive the emails. This increases the probability that a mail can still be delivered to the recipient domain. CNAME A CNAME Resource Record (CNAME RR) is used in the Domain Name System to assign an additional name to a domain. The abbreviation "CNAME" stands for canonical name (canonical = recognized, meaning the primary, quasi real name). In the simplest case, the name of a CNAME resource record refers to the name of an A resource record and/or an AAAA resource record. The names of these resource records refer to an IP address. When changing an IP address, only a single resource record needs to be changed for several names. An NS Resource Record, MX Resource Record or PTR Resource Record must not refer to a CNAME Resource Record. Conversely, a PTR resource record may only be accessible via a CNAME resource record. The name of a CNAME resource record may not be used as the name of other resource records, as it is representative of all resource records of the target.
Value:	mail.anyideas.de.	The domain to which the IP address should point A dot "." is appended to the domain (=Top-Level)
		Closes the dialog for the DNS record
		Closes the dialog for editing the zone
The creation of the PTR-RR is now complete and the firewall will change the IP to the desired domain on request!
Test PTR-RR
Test the created PTR-RR under: Network Network Tools  Area Host Settings			Network tools UTMuser@firewall.name.fqdnNetwork
Query type	PTR	Query type of the created DNS record
Hostname:	192.168.222.60	IP address of the desired server
Nameserver:	127.0.0.1	Localhost address of the UTM
Response
In the lower window, if everything has been set up correctly, the IP address is resolved to the correct domain. Alternatively by a nslookup 192.168.222.60 from a computer in the UTM network
Relay-Zone A relay zone is responsible for forwarding requests that belong to a specific domain. Application example: The firewall is used as a nameserver by all clients in the internal network In addition, a nameserver is integrated in the internal network which is responsible for the internal domain administration (anyideas.local) If a client now wants to resolve an internal name (e.g.: uma.anyideas.local), this DNS request is sent to the firewall By forwarding all queries to anyideas.local to the internal nameserver, they can be resolved by the latter without any problems Requests that do not belong to the internal domain are still resolved by the firewall itself Create Relay
Application Nameserver  Area Zones Button Add Relay-Zone
Caption	Value	Description	Add Relay-Zone UTMuser@firewall.name.fqdnApplicationNameserver
Zone name:	anyideas.local	Domain that is managed by an internal DNS server
Type	Relay	Zone type is Relay
Server Add server
IP address:	192.168.222.5	IP address (IPv4 or IPv6) of the internal DNS server	Add server UTMuser@firewall.name.fqdnApplicationNameserver
Port:	53	Default: 53 for DNS queries
		Saves the information and closes the dialog
			Nameserver UTMuser@firewall.name.fqdnApplication Nameserver with relay zones for IPv4 and IPv6

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DNS-Server

. | Menu Network Server Settings  Area Server Settings section

DNS-Server

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DNS Forwarding

A DNS forwarding is used to forward all DNS requests made to the firewall's name server to another IP.

Add DNS Forwarding

Menu Applications Nameserver  Area DNS Forwarding Button + Add DNS Forwarding

Caption	Value	Description	Add DNS Forwarding UTMuser@firewall.name.fqdnApplicationNameserver Creating a DNS Forwarding
IP address:	192.168.175.2	Click on Add server and in the IP address field the address of the remote name server is entered Edit the entry trash Delete the entry
		Saves the entry

Domain forwarding through a VPN tunnel

Sometimes it is necessary to forward internal domain requests to a remote name server located in a VPN.

It should be noted here that, by default, all direct requests addressed to external name servers are sent from the firewall with the external IP. However, a public IP is not routed into a VPN tunnel.

Set the name server of the firewall

Caption	Value	Description	Server settings UTMuser@firewall.name.fqdnNetwork Name server IP
Check name server before local cache:	Yes	Should be enabled
Primary name server:	127.0.0.1	The IP of the UTM itself (localhost=127.0.0.1)
Secondary name server:		Can remain empty or designate another DNS in the VPN
		Saves the entry

Create relay

notempty

For this example, an IPSec connection was used. For SSL-VPN, the setup is done in the same way.

Menü Menu Applications Name server  Area Zones Button + Add Relay-Zone.

Caption	Value	Description	Add relay zone UTMuser@firewall.name.fqdnApplicationNameserver Creating the relay zone
Zone name:	relay.test.local	Zone name of the desired domain
Type:	Relay	Select this type
IP address:	192.168.8.5	Click on Add server and in the IP address field the address of the remote name server is entered Edit the entry trash Delete the entry
		Saves the entry

Create network object

Menu Firewall Network Objects  Button + Add Object. A network object must be created for the IPSec network.

Caption	Value	Description	Add Network Objects UTMuser@firewall.name.fqdnFirewallNetwork object Network object
Name:	IPSec-Network	Choose unique name
Type:	VPN network	Select this type
Address:	192.168.8.0/24	The IP address corresponds to that of the IPSec network
Zone:	vpn-ipsec	Suitable zone must be selected
		Saves the entry

Add Rule

In the last step, a firewall rule with a Hide NAT must be created. This causes the DNS forwarding to also go into the tunnel, and not directly into the Internet.
Menu Firewall Packetfilter  Button + Add Rule.

Caption	Value	Add Rule UTMuser@firewall.name.fqdnFirewallPacketfilter
Aktive:	On
Source:	external-interface
Destination:	IPSec-Netzwerk
Service:	domain-udp
[-] NAT
Type:	HIDENAT
Network object:	internal-interface
	Saves the rule and closes the dialogue. The rules must then be updated.

Safe Search with external DHCP server

If an external DHCP server is used, the active web filter Safe Search often does not work for search engines, especially Google, when searching for images.
In order for this web filter to take effect there as well, the following forward zones must be set up for all ccTLDs (see https://www.google.com/supported_domains : www.google.de, www.google.ch, ...).
Menu Applications Nameserver  Button + Add Forward Zone.

Caption	Value	Zone bearbeiten UTMuser@firewall.name.fqdnApplicationNameserver The forward zone set up for www.google.com
Zone name:	www.google.com
Name server hostname:	localhost
Name server IP address:
In the Name server window, click in the www.google.de zone. In the Edit Zone window click Add entry.
Name:	www.google.com
Type:	A
Value:	216.239.38.120
Save and click again on Add entry.
Name:	www.google.com
Type:	AAAA
Value:	2001:4860:4802:32::78
	Saves the entry

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DNA rebinding attack and prevention

This type of attack attempts to gain access to internal resources using falsified DNS responses.

The attacker needs nothing more than a domain with malicious code and a name server that answers all DNS queries for the attacker site.

The attack is carried out in several steps:
1. the victim is lured to a prepared website whose IP address is only marked as valid for a few seconds.
2. Malicious code is loaded on the website, which starts a new call after the IP address has expired,
3. but which now uses a modified, proprietary DNS server to display an address from the victim's local network as the destination
4. The attacker now has access to the host with the internal IP through his malicious code (e.g. Java script)

  

DNS rebinding prevention prevents internal IP addresses from the local network from being issued in response to a DNS query.

Configuration

DNS Rebinding Prevention is configured under Applications Nameserver  Area DNS Rebinding Prevention.

Caption	Value	Description	Nameserver UTMuser@firewall.name.fqdnApplications DNS Rebinding Prevention tab
DNS Rebinding Prevention:	On default	Activates DNS rebinding prevention
Mode:	Automatic	In the factory settings, all private IP addresses (class A, B and C) are blocked. The corresponding private IPv6 addresses and the unique local unicast address are also protected in automatic mode.
	Custom	The addresses can be set manually.
Protected addresses:		All addresses that are protected by the prevention are displayed here.
		Saves the settings
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mDNS-Repeater

Applications Nameserver  Area mDns-Repeater
The multicast DNS repeater forwards mDNS queries between interfaces and networks without the need to configure an extra DNS server.
Multicast-capable devices, such as printers, can be made visible across different networks.

The mDNS repeater only uses port 5353 as source and destination port!

Caption	Value	Description	Nameserver UTMuser@firewall.name.fqdnApplications mDNS repeater configuration
Activate mDNS repeater:	Yes	Activates the multicast DNS repeater
		The mDNS repeater is active
		The mDNS repeater is deactivated
Interface:	×LAN1 ×LAN2	Selection of the interfaces between which mDNS requests are to be forwarded. At least two interfaces must be entered.
Default behavior for networks:	default	All networks connected to the interfaces use the mDNS repeater
Blocked network exceptions:		Networks from which mDNS requests are not forwarded
Allowed network exceptions: Only if Default behavior for all networks is deactivated		Explicit specification of the networks from which mDNS requests are forwarded

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General Settings
General settings are made under Applications Nameserver  Area General.
Caption	Value	Description	Nameserver UTMuser@firewall.name.fqdnAnwendungen Tab General
DNSSEC validation in resolver:	Off	notempty Caution! If DNSSEC Validation is enabled alongside Forward-Zones, it must be ensured that the domains corresponding to the forward zones can be validated within the global DNS. Replies corresponding to not globally registered domains are refused and lead to SERVFAIL replies for the domain in question. When this function is activated, all DNS entries are resolved with DNSSEC without exception. This would also attempt a validation in the DNS hierarchy for only local addresses. However, due to the lack of uniqueness of the local address, it cannot be registered with higher-level DNS servers. An error message appears, the address is not resolved and the zone is therefore not accessible (using DNS). This applies, for example, to .local domains! Further information on the implementation of DNSSEC can be found here.
Allow DNS queries only from routed and VPN networks:	On Default	By default, only DNS queries from the following sources are answered: localhost local networks Networks that are routed via another gateway but do not contain a default route (or shared default route) VPN transfer networks or Roadwarrior address pools
	Off	If DNS queries are to be answered from other external networks as well, this option must be disabled
Disable EDNS for the following servers:		EDNS can be disabled for servers that do not comply with RFC 6891. Old or misconfigured name servers sometimes do not use or do not correctly use Extended DNS and as a result do not accept DNS queries that use these protocol extensions. EDNS is mandatory for DNSSEC The DO flag (DNSSEC OK) can no longer be placed in the standard header.
notempty New as of v12.6.0 Use DNS server specified by the provider:	Off	When activated, the DNS server of the Internet provider is used.

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