Presented by
Greg Lindsay
Technical Writer
Windows Server Information Experience
Presented at:
Seattle Windows Networking User Group April 7, 2010
Windows 7 DNS client
DNS devolution
Security-awareness: DNSSEC
What is it?
“A behavior in Active Directory environments that allows client computers that
are members of a child namespace to access resources in the parent namespace without the need to explicitly provide the fully qualified domain name (FQDN) of the resource.”
What is different?
Windows 7 introduces the concept of a devolution level.
The devolution level can be configured. If not set, then the devolution level is
determined automatically according to a set of rules based on the number of labels in the forest root domain (FRD) and the primary DNS suffix.
By default, devolution now proceeds down to the FRD name and no further. Previously, the effective devolution level was always 2.
Why the change?
To prevent inadvertently treating systems outside of the organizational boundary as though they were internal.
This update is also available for previous operating systems. See Microsoft Security Advisory 971888: Update for DNS Devolution.
Example
FRD:
corp.contoso.com
Primary DNS suffix:
east.corp.contoso.com
Devolution level as determined by rule: 3
An application attempting to query the
hostname
srv7
will attempt to resolve
srv7.east.corp.contoso.com
and
srv7.corp.contoso.com
.
Previously, an attempt was also made to
resolve
srv7.contoso.com
.
Devolution is not enabled if:
A global suffix search list is configured.
Append parent suffixes of the primary DNS suffix
is not selected in advanced TCP/IP settings.
The Windows 7 DNS client is a “Non-validating security-aware
stub resolver.”
Non-validating: The client will not validate on its own that DNS responses
have not been modified in transit.
The non-validating DNS client relies on a DNS server to perform DNS
security extensions (DNSSEC) signature validation.
Security-aware: The client is capable of establishing a secured channel to a
security-aware name server.
The security-aware client will expect the DNS server to indicate results of the
DNSSEC validation when returning the response. This is done by setting the
Authenticated Data (AD) bit in the response. If the DNS server fails to
validate successfully (as indicated by the AD bit not being set in the
response), the DNS client can reject the response.
Stub resolver: The client does not perform recursion itself but rather relies on
the DNS server to perform recursion as defined in RFC1034, section 5.3.1.
Authoritative DNS Local Recursive DNS Cache
Attacker
Query
Authentic
Response
Recursive
query
Authentic
Response
Spoofed
Responses
Spoofed
Responses
DNS does not
inherently
provide security
DNSSEC validation Authoritative DNS Local Recursive DNS Cache DNS query Validation requested
Authentic
Response
Recursive DNS query Authentic, validatedResponse anchorTrust
A Windows Server 2008 R2 DNS server deployed as a forwarder or a recursive DNS
server retrieves DNSKEY resource records required to perform DNSSEC validation if it receives a query for information in a zone for which it has a configured trust anchor.
Spoofed responses to queries for DNSSEC protected zones will fail validation because
they cannot provide the correct DNSKEY RRs.
The Windows 7 DNS client can be configured to fail queries that are not successfully
validated using a new feature in Windows Server 2008 R2 called the Name Resolution Policy Table (NRPT).
For more information, see Understanding DNSSEC in Windows
(http://technet.microsoft.com/en-us/library/ee649277(WS.10).aspx).
DNSKEY
DirectAccess is a new feature in Windows 7 and Windows Server 2008 R2 that enables
users to access corporate resources anytime they have an internet connection, without the need to establish a VPN connection.
DirectAccess uses a new feature in Windows Server 2008 R2 called the Name Resolution
Policy Table (NRPT)to define DNS policy settings so that you can separate Internet traffic from intranet traffic.
NRPT rules define DNS client behavior for specific namespaces. You can specify policy
settings for a certain DNS suffix, prefix, FQDN, or IPv4 and IPv6 subnet.
Internet
intranet
DirectAccess server
Computer Configuration \Policies\Windows Settings\Name Resolution Policy
Workgroup clients can obtain settings from Local Group Policy.
**Do not use Local Group Policy Editor as this is currently bugged.
Group Policy:
HKLM\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient\DnsPolicyConfig
Local Group Policy:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Dnscache\Parameters\DnsPolicyConfig
View policy settings
Netsh namespace show policy
Netsh namespace show effectivepolicy Netsh dns show state
Namespace (required)
Suffix, prefix, FQDN, subnet
Certification authority
(optional)
Used with IPsec
Enable DNSSEC or
Enable DirectAccess
(required)
Require validation
(optional)
Use IPsec (optional)
Encryption type: none, low, medium, high
DNS servers (optional)
Conditional forwarding
Web proxy(optional)
For HTTP traffic
Use IPsec (optional)
Encryption type: none, low, medium, high
Advanced global policy settings are
not applied to DNSSEC rules
Network Location Dependency
Always and never use DA settings in the NRPT are mostly for debugging purposes
Query Failure
When you fail a query on a public network and fall back, there is a risk of being redirected.
