-
This is a
-followup
-on my
-previous
-work on
-merging
-all the computer related LDAP objects in Debian Edu.
-
-
As a step to try to see if it possible to merge the DNS and DHCP
-LDAP objects, I have had a look at how the packages pdns-backend-ldap
-and dhcp3-server-ldap in Debian use the LDAP server. The two
-implementations are quite different in how they use LDAP.
-
-To get this information, I started slapd with debugging enabled and
-dumped the debug output to a file to get the LDAP searches performed
-on a Debian Edu main-server. Here is a summary.
-
-
powerdns
-
-
Clues
-on how to set up PowerDNS to use a LDAP backend is available on
-the web.
-
-
PowerDNS have two modes of operation using LDAP as its backend.
-One "strict" mode where the forward and reverse DNS lookups are done
-using the same LDAP objects, and a "tree" mode where the forward and
-reverse entries are in two different subtrees in LDAP with a structure
-based on the DNS names, as in tjener.intern and
-2.2.0.10.in-addr.arpa.
-
-
In tree mode, the server is set up to use a LDAP subtree as its
-base, and uses a "base" scoped search for the DNS name by adding
-"dc=tjener,dc=intern," to the base with a filter for
-"(associateddomain=tjener.intern)" for the forward entry and
-"dc=2,dc=2,dc=0,dc=10,dc=in-addr,dc=arpa," with a filter for
-"(associateddomain=2.2.0.10.in-addr.arpa)" for the reverse entry. For
-forward entries, it is looking for attributes named dnsttl, arecord,
-nsrecord, cnamerecord, soarecord, ptrrecord, hinforecord, mxrecord,
-txtrecord, rprecord, afsdbrecord, keyrecord, aaaarecord, locrecord,
-srvrecord, naptrrecord, kxrecord, certrecord, dsrecord, sshfprecord,
-ipseckeyrecord, rrsigrecord, nsecrecord, dnskeyrecord, dhcidrecord,
-spfrecord and modifytimestamp. For reverse entries it is looking for
-the attributes dnsttl, arecord, nsrecord, cnamerecord, soarecord,
-ptrrecord, hinforecord, mxrecord, txtrecord, rprecord, aaaarecord,
-locrecord, srvrecord, naptrrecord and modifytimestamp. The equivalent
-ldapsearch commands could look like this:
-
-
-ldapsearch -h ldap \
- -b dc=tjener,dc=intern,ou=hosts,dc=skole,dc=skolelinux,dc=no \
- -s base -x '(associateddomain=tjener.intern)' dNSTTL aRecord nSRecord \
- cNAMERecord sOARecord pTRRecord hInfoRecord mXRecord tXTRecord \
- rPRecord aFSDBRecord KeyRecord aAAARecord lOCRecord sRVRecord \
- nAPTRRecord kXRecord certRecord dSRecord sSHFPRecord iPSecKeyRecord \
- rRSIGRecord nSECRecord dNSKeyRecord dHCIDRecord sPFRecord modifyTimestamp
-
-ldapsearch -h ldap \
- -b dc=2,dc=2,dc=0,dc=10,dc=in-addr,dc=arpa,ou=hosts,dc=skole,dc=skolelinux,dc=no \
- -s base -x '(associateddomain=2.2.0.10.in-addr.arpa)'
- dnsttl, arecord, nsrecord, cnamerecord soarecord ptrrecord \
- hinforecord mxrecord txtrecord rprecord aaaarecord locrecord \
- srvrecord naptrrecord modifytimestamp
-
-
-
In Debian Edu/Lenny, the PowerDNS tree mode is used with
-ou=hosts,dc=skole,dc=skolelinux,dc=no as the base, and these are two
-example LDAP objects used there. In addition to these objects, the
-parent objects all th way up to ou=hosts,dc=skole,dc=skolelinux,dc=no
-also exist.
-
-
-dn: dc=tjener,dc=intern,ou=hosts,dc=skole,dc=skolelinux,dc=no
-objectclass: top
-objectclass: dnsdomain
-objectclass: domainrelatedobject
-dc: tjener
-arecord: 10.0.2.2
-associateddomain: tjener.intern
-
-dn: dc=2,dc=2,dc=0,dc=10,dc=in-addr,dc=arpa,ou=hosts,dc=skole,dc=skolelinux,dc=no
-objectclass: top
-objectclass: dnsdomain2
-objectclass: domainrelatedobject
-dc: 2
-ptrrecord: tjener.intern
-associateddomain: 2.2.0.10.in-addr.arpa
-
-
-
In strict mode, the server behaves differently. When looking for
-forward DNS entries, it is doing a "subtree" scoped search with the
-same base as in the tree mode for a object with filter
-"(associateddomain=tjener.intern)" and requests the attributes dnsttl,
-arecord, nsrecord, cnamerecord, soarecord, ptrrecord, hinforecord,
-mxrecord, txtrecord, rprecord, aaaarecord, locrecord, srvrecord,
-naptrrecord and modifytimestamp. For reverse entires it also do a
-subtree scoped search but this time the filter is "(arecord=10.0.2.2)"
-and the requested attributes are associateddomain, dnsttl and
-modifytimestamp. In short, in strict mode the objects with ptrrecord
-go away, and the arecord attribute in the forward object is used
-instead.
-
-
The forward and reverse searches can be simulated using ldapsearch
-like this:
-
-
-ldapsearch -h ldap -b ou=hosts,dc=skole,dc=skolelinux,dc=no -s sub -x \
- '(associateddomain=tjener.intern)' dNSTTL aRecord nSRecord \
- cNAMERecord sOARecord pTRRecord hInfoRecord mXRecord tXTRecord \
- rPRecord aFSDBRecord KeyRecord aAAARecord lOCRecord sRVRecord \
- nAPTRRecord kXRecord certRecord dSRecord sSHFPRecord iPSecKeyRecord \
- rRSIGRecord nSECRecord dNSKeyRecord dHCIDRecord sPFRecord modifyTimestamp
-
-ldapsearch -h ldap -b ou=hosts,dc=skole,dc=skolelinux,dc=no -s sub -x \
- '(arecord=10.0.2.2)' associateddomain dnsttl modifytimestamp
-
-
-
In addition to the forward and reverse searches , there is also a
-search for SOA records, which behave similar to the forward and
-reverse lookups.
-
-
A thing to note with the PowerDNS behaviour is that it do not
-specify any objectclass names, and instead look for the attributes it
-need to generate a DNS reply. This make it able to work with any
-objectclass that provide the needed attributes.
-
-
The attributes are normally provided in the cosine (RFC 1274) and
-dnsdomain2 schemas. The latter is used for reverse entries like
-ptrrecord and recent DNS additions like aaaarecord and srvrecord.
-
-
In Debian Edu, we have created DNS objects using the object classes
-dcobject (for dc), dnsdomain or dnsdomain2 (structural, for the DNS
-attributes) and domainrelatedobject (for associatedDomain). The use
-of structural object classes make it impossible to combine these
-classes with the object classes used by DHCP.
-
-
There are other schemas that could be used too, for example the
-dnszone structural object class used by Gosa and bind-sdb for the DNS
-attributes combined with the domainrelatedobject object class, but in
-this case some unused attributes would have to be included as well
-(zonename and relativedomainname).
-
-
My proposal for Debian Edu would be to switch PowerDNS to strict
-mode and not use any of the existing objectclasses (dnsdomain,
-dnsdomain2 and dnszone) when one want to combine the DNS information
-with DHCP information, and instead create a auxiliary object class
-defined something like this (using the attributes defined for
-dnsdomain and dnsdomain2 or dnszone):
-
-
-objectclass ( some-oid NAME 'dnsDomainAux'
- SUP top
- AUXILIARY
- MAY ( ARecord $ MDRecord $ MXRecord $ NSRecord $ SOARecord $ CNAMERecord $
- DNSTTL $ DNSClass $ PTRRecord $ HINFORecord $ MINFORecord $
- TXTRecord $ SIGRecord $ KEYRecord $ AAAARecord $ LOCRecord $
- NXTRecord $ SRVRecord $ NAPTRRecord $ KXRecord $ CERTRecord $
- A6Record $ DNAMERecord
- ))
-
-
-
This will allow any object to become a DNS entry when combined with
-the domainrelatedobject object class, and allow any entity to include
-all the attributes PowerDNS wants. I've sent an email to the PowerDNS
-developers asking for their view on this schema and if they are
-interested in providing such schema with PowerDNS, and I hope my
-message will be accepted into their mailing list soon.
-
-
ISC dhcp
-
-
The DHCP server searches for specific objectclass and requests all
-the object attributes, and then uses the attributes it want. This
-make it harder to figure out exactly what attributes are used, but
-thanks to the working example in Debian Edu I can at least get an idea
-what is needed without having to read the source code.
-
-
In the DHCP server configuration, the LDAP base to use and the
-search filter to use to locate the correct dhcpServer entity is
-stored. These are the relevant entries from
-/etc/dhcp3/dhcpd.conf:
-
-
-ldap-base-dn "dc=skole,dc=skolelinux,dc=no";
-ldap-dhcp-server-cn "dhcp";
-
-
-
The DHCP server uses this information to nest all the DHCP
-configuration it need. The cn "dhcp" is located using the given LDAP
-base and the filter "(&(objectClass=dhcpServer)(cn=dhcp))". The
-search result is this entry:
-
-
-dn: cn=dhcp,dc=skole,dc=skolelinux,dc=no
-cn: dhcp
-objectClass: top
-objectClass: dhcpServer
-dhcpServiceDN: cn=DHCP Config,dc=skole,dc=skolelinux,dc=no
-
-
-
The content of the dhcpServiceDN attribute is next used to locate the
-subtree with DHCP configuration. The DHCP configuration subtree base
-is located using a base scope search with base "cn=DHCP
-Config,dc=skole,dc=skolelinux,dc=no" and filter
-"(&(objectClass=dhcpService)(|(dhcpPrimaryDN=cn=dhcp,dc=skole,dc=skolelinux,dc=no)(dhcpSecondaryDN=cn=dhcp,dc=skole,dc=skolelinux,dc=no)))".
-The search result is this entry:
-
-
-dn: cn=DHCP Config,dc=skole,dc=skolelinux,dc=no
-cn: DHCP Config
-objectClass: top
-objectClass: dhcpService
-objectClass: dhcpOptions
-dhcpPrimaryDN: cn=dhcp, dc=skole,dc=skolelinux,dc=no
-dhcpStatements: ddns-update-style none
-dhcpStatements: authoritative
-dhcpOption: smtp-server code 69 = array of ip-address
-dhcpOption: www-server code 72 = array of ip-address
-dhcpOption: wpad-url code 252 = text
-
-
-
Next, the entire subtree is processed, one level at the time. When
-all the DHCP configuration is loaded, it is ready to receive requests.
-The subtree in Debian Edu contain objects with object classes
-top/dhcpService/dhcpOptions, top/dhcpSharedNetwork/dhcpOptions,
-top/dhcpSubnet, top/dhcpGroup and top/dhcpHost. These provide options
-and information about netmasks, dynamic range etc. Leaving out the
-details here because it is not relevant for the focus of my
-investigation, which is to see if it is possible to merge dns and dhcp
-related computer objects.
-
-
When a DHCP request come in, LDAP is searched for the MAC address
-of the client (00:00:00:00:00:00 in this example), using a subtree
-scoped search with "cn=DHCP Config,dc=skole,dc=skolelinux,dc=no" as
-the base and "(&(objectClass=dhcpHost)(dhcpHWAddress=ethernet
-00:00:00:00:00:00))" as the filter. This is what a host object look
-like:
-
-
-dn: cn=hostname,cn=group1,cn=THINCLIENTS,cn=DHCP Config,dc=skole,dc=skolelinux,dc=no
-cn: hostname
-objectClass: top
-objectClass: dhcpHost
-dhcpHWAddress: ethernet 00:00:00:00:00:00
-dhcpStatements: fixed-address hostname
-
-
-
There is less flexiblity in the way LDAP searches are done here.
-The object classes need to have fixed names, and the configuration
-need to be stored in a fairly specific LDAP structure. On the
-positive side, the invidiual dhcpHost entires can be anywhere without
-the DN pointed to by the dhcpServer entries. The latter should make
-it possible to group all host entries in a subtree next to the
-configuration entries, and this subtree can also be shared with the
-DNS server if the schema proposed above is combined with the dhcpHost
-structural object class.
-
-
Conclusion
-
-
The PowerDNS implementation seem to be very flexible when it come
-to which LDAP schemas to use. While its "tree" mode is rigid when it
-come to the the LDAP structure, the "strict" mode is very flexible,
-allowing DNS objects to be stored anywhere under the base cn specified
-in the configuration.
-
-
The DHCP implementation on the other hand is very inflexible, both
-regarding which LDAP schemas to use and which LDAP structure to use.
-I guess one could implement ones own schema, as long as the
-objectclasses and attributes have the names used, but this do not
-really help when the DHCP subtree need to have a fairly fixed
-structure.
-
-
Based on the observed behaviour, I suspect a LDAP structure like
-this might work for Debian Edu:
-
-
-ou=services
- cn=machine-info (dhcpService) - dhcpServiceDN points here
- cn=dhcp (dhcpServer)
- cn=dhcp-internal (dhcpSharedNetwork/dhcpOptions)
- cn=10.0.2.0 (dhcpSubnet)
- cn=group1 (dhcpGroup/dhcpOptions)
- cn=dhcp-thinclients (dhcpSharedNetwork/dhcpOptions)
- cn=192.168.0.0 (dhcpSubnet)
- cn=group1 (dhcpGroup/dhcpOptions)
- ou=machines - PowerDNS base points here
- cn=hostname (dhcpHost/domainrelatedobject/dnsDomainAux)
-
-
-
This is not tested yet. If the DHCP server require the dhcpHost
-entries to be in the dhcpGroup subtrees, the entries can be stored
-there instead of a common machines subtree, and the PowerDNS base
-would have to be moved one level up to the machine-info subtree.
-
-
The combined object under the machines subtree would look something
-like this:
-
-
-dn: dc=hostname,ou=machines,cn=machine-info,dc=skole,dc=skolelinux,dc=no
-dc: hostname
-objectClass: top
-objectClass: dhcpHost
-objectclass: domainrelatedobject
-objectclass: dnsDomainAux
-associateddomain: hostname.intern
-arecord: 10.11.12.13
-dhcpHWAddress: ethernet 00:00:00:00:00:00
-dhcpStatements: fixed-address hostname.intern
-
-
-One could even add the LTSP configuration associated with a given
-machine, as long as the required attributes are available in a
-auxiliary object class.
+
Just got an email from Tobias Gruetzmacher as a followup on my
+previous
+post about sshfs. He reported another problem with sshfs. It
+fail to handle hard links properly. A simple way to spot this is to
+look at the . and .. entries in the directory tree. These should have
+a link count >1, but on sshfs the count is 1. I just tested to see
+what happen when trying to hardlink, and this fail as well:
+
+
+% ln foo bar
+ln: creating hard link `bar' => `foo': Function not implemented
+%
+
+
+
I have not yet found time to implement a test for this in my file
+system test code, but believe having working hard links is useful to
+avoid surprised unix programs. Not as useful as working file locking
+and symlinks, which are required to get a working desktop, but useful
+nevertheless. :)
+
+
The latest version of the file system test code is available via
+git from
+http://github.com/gebi/fs-test