Windows DNS How To Block Queries Or domains
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Log in to Windows Server 2016 with an account that has DNS administrator permissions and open a PowerShell prompt. The policy below will create a filter that blocks resolution of the malware.com domain. Note the use of IGNORE for the -Action parameter, and EQ is a logical operator that means equals.
In all cases, the DNS queries which are defined to move through the tunnel, go to any DNS servers which are defined by ASA. If there are no DNS servers defined by the ASA, then the DNS settings are blank for the tunnel. If you do not have split DNS defined, then all of the DNS queries are sent to the DNS servers which are defined by the ASA. However, the behaviors that are described in this document can be different, depending upon the Operating System (OS).
Refer to Cisco bug ID CSCtn14578, currently resolved on Microsoft Windows only, as of Version 3.0(4235). The solution implements true split DNS, it strictly queries the configured domain names that matches and are allowed to the VPN DNS servers. All other queries are only allowed to other DNS servers, such as those configured on the physical adapter(s).
This issue is due to the native DNS client that attempts to send DNS queries via the physical adapter, which AnyConnect blocks (given the tunnel-all configuration). This leads to a name resolution delay that can be significant, especially if a large number of DNS suffixes are pushed by the headend. The DNS client must walk through all of the queries and available DNS servers until it receives a positive response.
On Microsoft Windows systems, DNS settings are per-interface. If split tunneling is used, DNS queries can fall back to the physical adaptor DNS servers after they fail on the VPN tunnel adaptor. If split tunneling without split DNS is defined, then both internal and external DNS resolution works because it falls back to the external DNS servers.
DNS requests, which matches with the split-dns domains are allowed to tunnel DNS servers, but are not allowed to other DNS servers. To prevent such internal DNS queries from leaking out the tunnel, the AnyConnect driver responds with "no such name" if the query is sent to other DNS servers. Therefore, the split-dns domains can only be resolved via tunnel DNS servers.
On Macintosh systems, the DNS settings are global. If split tunneling is used, but split DNS is not used, it is not possible for the DNS queries to reach DNS servers outside of the tunnel. You can only resolve internally, not externally.
AnyConnect does not interfere with the native DNS resolver. The tunnel DNS servers are configured as preferred resolvers, which takes precedence over public DNS servers, thus it ensures that the initial DNS request for a name resolution is sent over the tunnel. Since DNS settings are global on Mac OS X, it is not possible for DNS queries to use public DNS servers outside the tunnel as documented in CSCtf20226 . To start with AnyConnect 4.2, host routes for the Tunnel DNS server(s) are automatically added as split-include networks (secure routes) by the AnyConnect client, and therefore the split-include access-list no longer requires explicit addition of the tunnel DNS server subnet.
AnyConnect does not interfere with the native DNS resolver. The tunnel DNS servers are configured as preferred resolvers, taking precedence over public DNS servers, thus it ensures that the initial DNS request for a name resolution is sent over the tunnel. Since DNS settings are global on Mac OS X, it is not possible for DNS queries to use public DNS servers outside the tunnel as documented in CSCtf20226 . To start with AnyConnect 4.2, host routes for the Tunnel DNS server(s) are automatically added as split-include networks (secure routes) by the AnyConnect client, and therefore the split-include access-list no longer requires explicit addition of the tunnel DNS server subnet.
The iPhone is the complete opposite of the Macintosh system and is not similar to Microsoft Windows. If split tunneling is