DNS Zones

DNS Zones

• DNS records kept in zones• DNS server is authoritative for a domain if it

hosts the zone for that domain• Sub-domains can be kept in same zone as long

as they are contiguous– Example: west.Company.com can be kept in

the same zone as Company.com.

DNS Zones Continued

• Zones are either “Forward Lookup” or “Reverse Lookup” – “Forward Lookup” zones resolve FQDNs to

IP addresses– “Reverse Lookup” zones resolve IP

addresses to FQDNs

FQDNs vs IP Addresses

Client1.company.com

192.168.1.10/24

Tips

• “Reverse Lookup” zones are written backwards.

This zone would provide IP to FQDN name resolution for the 192.168.1.0 network.

Tips Continued

• The DNS server in an nslookup command is listed as “UnKnown” unless you create a reverse lookup zone.

DNS Zones Continued

• There are two main types of zones that can be created:– Standard zones–Active Directory Integrated zones

Recap

• DNS Records kept in zones• “Forward lookup:” Name to IP• “Reverse lookup:” IP to name–Written backwards

• Each can have either Standard or Active Directory Integrated (ADI) zones

Standard Zones

Standard Zones

• Standard zones kept in text files in %systemroot%\system32\dns named domain name.dns.

Standard Zones Continued

• Two types of Standard zones:– Standard Primary: only read/write copy of

the zone– Standard Secondary: read-only, used for

fault tolerance and load balancing.

Standard Zones Continued

• Modifications to Standard zones must be made on the Primary

• Clients can only update records by contacting the Primary

• Updates to the Primary are sent to the Secondary using zone transfers

Zone Transfers

• Two triggers for zone transfers:–Refresh Interval–DNS Notify

• Zone transfers:–Require permission–Always initiated by the Secondary zone

Zone Transfers Continued

Zone Transfers Continued

Zone Transfers Continued

Zone Transfers Continued

• Best security: “Allow zone transfers:” “Only to the following servers”

• Second choice: “Allow zone transfers:” “Only to servers listed on the Name Servers tab”

• Avoid “Allow zone transfers:” “To any server”

Zone Transfers Continued• The “Name Servers” tab lists authoritative

DNS servers

Zone Transfers Continued

1. Secondary requests a copy of Primary’s “Start of Authority” (SOA) record– “Serial number:” starts at 1 and increments

to infinity2. If “Serial number:” on Primary is higher than

Secondary’s, Secondary initiates zone transfer

Zone Transfers Continued

Zone Transfers Continued

• Zone transfers are in clear text.• The only way to secure them would be a

“Connection Security Rule” (IPSec)

Recap

• Standard Primary – only read/write• Standard Secondary – read only• Primary transfers changes to Secondary using

zone transfers:–Need permission for copy of zone – Initiated by Secondary server–Not secure

Active Directory Integrated Zones

ADI

Active Directory Integrated Zones (ADI)

• ADI zones store DNS in Active Directory–Only created on Domain Controllers–Changes exchanged through AD replication–No permission needed

• Three main benefits:–Multi-master– Secure “zone transfers”– Secure dynamic updates

ADI Continued

ADI Continued

Tips

• Active Directory is a multi-master database: all copies of zone accept updates

• Any time clients must update records at more than one location requires ADI

ADI Continued

• DNS info transferred using replication, which is encrypted.

• “Zone transfers” automatically secure

ADI Continued

• Dynamic updates allow clients to update DNS records

• Secure Dynamic Updates record the SID of the client on the DNS record–Only that client can update record

• Secure Dynamic Updates can only be enforced on ADI zones

• To limit Dynamic Updates to domain members, allow only Secure Dynamic Updates

ADI Continued

ADI Continued

• Four replication scopes:– “To all DNS servers running on domain

controllers in this forest.”– “To all DNS servers running on domain

controllers in this domain.”– “To all domain controllers in this domain.”– “To all domain controllers in the scope of

this directory partition.”

Tips

• DNS info must be stored on less than all of DCs in domain, create a directory partition–Can also be created using ntdsutil

ADI Continued

ADI Continued

• Replication scope of “To all domain controllers in the scope of this directory partition,” must create new partition in AD

• Then, select which Domain Controllers receive a copy

ADI Continued• Create partition:

dnscmd /createdirectorypartition• Specify which DCS have a copy:

dnscmd /enlistdirectorypartition

ADI Continued

Recap

• ADI zones store DNS in Active Directory–Only created on Domain Controllers–Changes exchanged through AD replication–No permission needed

• Three main benefits:–Multi-master– Secure “zone transfers”– Secure dynamic updates

Recap Continued

• Four replication scopes:– “To all DNS servers running on domain

controllers in this forest.”– “To all DNS servers running on domain

controllers in this domain.”– “To all domain controllers in this domain.”– “To all domain controllers in the scope of

this directory partition.”• Less than all DCs in Domain