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FreeIPAv2:DNS Integration Design

FreeIPAv2 Development Documentation

Please note that this content was made during FreeIPAv2 development and it may no longer be relevant for current versions of FreeIPA. We left the content here for study and archaeological purposes.

Please check our Documentation for a recent list of topics.

Summary

The section Machine Identity in the IPAv2 PRD requires us to be able allow a machine to dynamically update its DNS record. This is pretty easy, but in order to do it in a secure manner, we have to ensure that a machine can only manipulate it's own record. For this, we have to establish the machines identity via kerberos. It is possible to use kerberos to authenticate the machine with DNS server using GSS-TSIG (RFC 3645). With the authenticity established, we will only allow the machine to edit it's own DNS record. The changes will then be stored in LDAP.

Dynamic updates with GSS-TSIG

GSS-TSIG (Generic Security Service Algorithm for Secret Key Transaction) is an authentication protocol for DNS, which is the extension to TSIG Protocol. The GSS-TSIG is a framework of GSS-API to provide authentication, integrity and confidentiality. It is defined in RFC 3645.

Support in dnspython

The dnspython library doesn't have support for GSS-TSIG. As a workaround, we could just make a simple wrapper for the nsupdate utility, but in the long-term, we should make a patch and work with upstream community on its adoption.

Storing DNS records in LDAP

Problem with BIND and LDAP is that there is currently no way of both reading and writing. There are two database interfaces, SDB and DLZ. SDB reads the data when BIND starts and holds them in cache. DLZ will look into the database with each query it gets. There are numerous drivers for each of these, LDAP included. Our choice is DLZ. The current LDAP driver for DLZ does not suit our need, mostly because of the schema it uses. We will need to write our own driver after we implement the write-back support for DLZ. We will design our own schema, inspired by the one SDB uses. Currently, all DLZ drivers are statically linked with BIND. We will patch BIND in such a way that these drivers can be loaded dynamically. This will allow us better control of schema we use and we will ship the driver ourselves.

LDAP driver

Here are some notes and things we should keep in mind when writing the driver.

  • LDAP driver should make as little ldap queries as possible, ldapi:// would be very handy.
  • The Serial information from the SOA record needs to be automatically generated whenever a record in the zone is changed. This would only be important for admins that run slaves for caching. Date would probably be best to use as a value. LDAP driver could update this with each change, but this might be slow, since we need to do additional query. Other way of solving this would be to have a DS plugin.
  • Every host is represented by one object, which can contain multiple DNS records. However, we should be prepared for multiple objects so that we allow different TTLs. It's not really important to also support writing such records, just to be able to handle them.
  • The LDAP driver should update the PTR record (if the zone exists and updates to the zone hosting the PTR are allowed). When A DNS Update is received first an update of the A(AAAA/A6) Record is performed. If that is successful, then a search for PTRRecord=<hostname> is performed. If the record is found and the IP address matches the record name, no further action is performed. If the IP address does not match and is of the same type as the update being performed (A/A6/AAAA) then it is deleted. Then a search for the provided IP address is performed to find a record, if is it found and it does not match it is updated. Finally if a PTR record is not found, a new one is created. WARNING: automatic PTR address removal might not be possible. Depending on how BIND is built internally we may not be able to know if a client is sending multiple IP addresses (multihomed system) so removing "older" PTR records may simply cause us to remove a PTR record we just set.
  • Careful with private IPv4 address. We need to explore if the driver has information about the ip address of the client that sent an update. In this case then we would never set the PTR record based on the sent ip address but only based on the ip address of the dns packet. This way there is no risk for client in a remote network using the VPN to try to update the wrong IP address (stupid private IP address spaces can cause problems). For IPV6 there is no such problem, so for A6/AAAA records we use the client provided information.

Schema

This schema is based on the SDB Schema.

attributetype ( 1.3.6.1.4.1.2428.20.0.0
	NAME 'dNSTTL'
	DESC 'An integer denoting time to live'
	EQUALITY integerMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
)

attributetype ( 1.3.6.1.4.1.2428.20.0.1
	NAME 'dNSClass'
	DESC 'The class of a resource record'
	EQUALITY caseIgnoreIA5Match
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.0.2
	NAME 'zoneName'
	DESC 'The name of a zone, i.e. the name of the highest node in the zone'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.0.3
	NAME 'relativeDomainName'
	DESC 'The starting labels of a domain name'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.12
	NAME 'pTRRecord'
	DESC 'domain name pointer, RFC 1035'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.13
	NAME 'hInfoRecord'
	DESC 'host information, RFC 1035'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.14
	NAME 'mInfoRecord'
	DESC 'mailbox or mail list information, RFC 1035'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.16
	NAME 'tXTRecord'
	DESC 'text string, RFC 1035'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.18
	NAME 'aFSDBRecord'
	DESC 'for AFS Data Base location, RFC 1183'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.24
	NAME 'SigRecord'
	DESC 'Signature, RFC 2535'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.25
	NAME 'KeyRecord'
	DESC 'Key, RFC 2535'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.28
	NAME 'aAAARecord'
	DESC 'IPv6 address, RFC 1886'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.29
	NAME 'LocRecord'
	DESC 'Location, RFC 1876'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.30
	NAME 'nXTRecord'
	DESC 'non-existant, RFC 2535'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.33
	NAME 'sRVRecord'
	DESC 'service location, RFC 2782'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.35
	NAME 'nAPTRRecord'
	DESC 'Naming Authority Pointer, RFC 2915'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.36
	NAME 'kXRecord'
	DESC 'Key Exchange Delegation, RFC 2230'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.37
	NAME 'certRecord'
	DESC 'certificate, RFC 2538'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.38
	NAME 'a6Record'
	DESC 'A6 Record Type, RFC 2874'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.39
	NAME 'dNameRecord'
	DESC 'Non-Terminal DNS Name Redirection, RFC 2672'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.43
	NAME 'dSRecord'
	DESC 'Delegation Signer, RFC 3658'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.44
	NAME 'sSHFPRecord'
	DESC 'SSH Key Fingerprint, draft-ietf-secsh-dns-05.txt'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.46
	NAME 'rRSIGRecord'
	DESC 'RRSIG, RFC 3755'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 1.3.6.1.4.1.2428.20.1.47
	NAME 'nSECRecord'
	DESC 'NSEC, RFC 3755'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
)

attributetype ( 2.16.840.1.113730.3.8.3.0
	NAME 'idnsName'
	DESC 'DNS FQDN'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.1
	NAME 'idnsAllowDynUpdate'
	DESC 'permit dynamic updates on this zone'
	EQUALITY booleanMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.2
	NAME 'idnsZoneActive'
	DESC 'define if the zone is considered in use'
	EQUALITY booleanMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.3
	NAME 'idnsSOAmName'
	DESC 'SOA Name'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.4
	NAME 'idnsSOArName'
	DESC 'SOA root Name'
	EQUALITY caseIgnoreIA5Match
	SUBSTR caseIgnoreIA5SubstringsMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.5
	NAME 'idnsSOAserial'
	DESC 'SOA serial number'
	EQUALITY numericStringMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.36
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.6
	NAME 'idnsSOArefresh'
	DESC 'SOA refresh value'
	EQUALITY numericStringMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.36
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.7
	NAME 'idnsSOAretry'
	DESC 'SOA retry value'
	EQUALITY numericStringMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.36
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.8
	NAME 'idnsSOAexpire'
	DESC 'SOA expire value'
	EQUALITY numericStringMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.36
	SINGLE-VALUE
)

attributetype ( 2.16.840.1.113730.3.8.3.9
	NAME 'idnsSOAminimum'
	DESC 'SOA minimum value'
	EQUALITY numericStringMatch
	SYNTAX 1.3.6.1.4.1.1466.115.121.1.36
	SINGLE-VALUE
)

objectclass ( 2.16.840.1.113730.3.8.4.0
	NAME 'idnsRecord'
	DESC 'dns Record, usually a host'
	SUP top
	STRUCTURAL
	MUST idnsName
	MAY ( cn $ idnsAllowDynUpdate $ DNSTTL $ DNSClass $ ARecord $
		AAAARecord $ A6Record $ NSRecord $ CNAMERecord $ PTRRecord $
		SRVRecord $ TXTRecord $ MXRecord $ MDRecord $ HINFORecord $
		MINFORecord $ AFSDBRecord $ SIGRecord $ KEYRecord $ LOCRecord $
		NXTRecord $ NAPTRRecord $ KXRecord $ CERTRecord $ DNAMERecord $
		DSRecord $ SSHFPRecord $ RRSIGRecord $ NSECRecord
	)
)

objectclass ( 2.16.840.1.113730.3.8.4.1
	NAME 'idnsZone'
	DESC 'Zone class'
	SUP idnsRecord
	STRUCTURAL
	MUST ( idnsName $ idnsZoneActive $ idnsSOAmName $ idnsSOArName $
		idnsSOAserial $ idnsSOArefresh $ idnsSOAretry $ idnsSOAexpire $
		idnsSOAminimum
	)
)

See also

Useful links