Tài liệu Advanced Network and System Administration ppt

1
Advanced Network and
System Administration
Accounts and
Namespaces
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Topics
1. What is a directory?
2. NIS
3. LDAP
4. OpenLDAP
5. LDAP Authentication
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What is a Directory?
Directory: A collection of information that is
primarily searched and read, rarely modified.
Directory Service: Provides access to
directory information.
Directory Server: Application that provides a
directory service.
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Directories vs. Databases

Directories are optimized for reading.

Databases balanced for read and write.

Directories are tree-structured.

Databases typically have relational structure.


Directories are usually replicated.

Databases can be replicated too.

Both are extensible data storage systems.

Both have advanced search capabilities.
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System Administration Directories

Types of directory data

Accounts

Mail aliases and lists (address book)

Cryptographic keys

IP addresses

Hostnames

Printers

Common directory services

DNS, LDAP, NIS
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Advantages of Directories


Make administration easier.

Change data only once: people, accounts, hosts.

Unify access to network resources.

Single sign on.

Single place for users to search (address book)

Improve data management

Improve consistency (one location vs many)

Secure data through only one server.
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NIS: Network Information Service

Originally called Sun Yellow Pages

Clients run ypbind

Servers run ypserv

Data stored under /var/yp on server.

Server shares NIS maps with clients

Each UNIX file may provide multiple maps


passwd: passwd.byname, passwd.byuid

Slave servers replicate master server content.

Easy to use, but insecure, difficult to extend.
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LDAP

Lightweight Directory Access Protocol

Lightweight compared to X.500 directories.

Directory, not a database.

Access Protocol, not a directory itself.
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LDAP Clients and Servers

LDAP Clients

Standalone directory browsers.

Embedded clients (mail clients, logins, etc.)

Cfg /etc/nsswitch.conf on UNIX to use LDAP.

Common LDAP servers

OpenLDAP


Fedora Directory Server (formerly Sun, Netscape)

Mac Open Directory

Microsoft ActiveDirectory

Novell eDirectory (NDS)
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LDAP Structure

An LDAP directory is made of entries.

Entries may be employee records, hosts, etc.

Each entries consists of attributes.

Attributes can be names, phone numbers, etc.

objectClass attribute identifies entry type.

Each attribute is a type / value pair.

Type is a label for the information stored (name)

Value is value for the attribute in this entry.

Attributes can be multi-valued.
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Tree-structure of LDAP Directories
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LDAP Schemas
Schemas specify allowed objectClasses and attributes.
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LDIF

LDAP Interchange Format.

Standard text format for storing LDAP
configuration data and directory contents.

LDIF Files

Collection of entries separated by blank lines.

Mapping of attribute names to values.

Uses

Import new data into directory.

Export directory to LDIF files for backups.
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LDIF Output Example
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Distinguished Names

Distinguished Names (DNs)

Uniquely identify an LDAP entry.


Provides path from LDAP root to the named entry.

Similar to an absolute pathname.

dn:cn=Jeff Foo,ou=Sales,dc=plainjoe,dc=org

Relative DNs (RDNs)

Any unique attribute pair in directory’s container.

ex: cn=Jeff Foo OR username=fooj

Similar to a relative pathname.

Except may have multiple components.

cn=Jane Smith+ou=Sales

cn=Jane Smith+ou=Engineering
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LDAP Client/Server Interaction
1. Client requests to bind to server.
2. Server accepts/denies bind request.
3. Client sends search request.
4. Server returns zero or more dir entries.
5. Server sends result code with any errors.
6. Client sends an unbind request.
7. Server sends result code and closes socket.
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LDAP Operations


Client Session Operations

Bind, unbind, and abandon

Query and Retrieval Operations

Search and compare

Modification Operations

Add, modify, modifyRDN, and delete
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Authentication
Anonymous Authentication
Binds with empty DN and password.
Simple Authentication
Binds with DN and password. Cleartext.
Simple Authentication over SSL/TLS
Use SSL to encrypt simple authentication.
Simple Authentication and Security Layer
SASL is an extensible security scheme.
SASL mechanisms: Kerberos, GSSAPI, SKEY
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Distributed Directories

Use multiple LDAP servers.

Why distribute?


Throughput

More servers can reduce load on any single server.

Latency

Have local server serve local data to LAN.

Only use WAN for non-local data on other servers.

Administrative Boundaries

Let each side administrate their own directory.
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OpenLDAP

Open source LDAPv3 server.

LDAP server: slapd

Client commands: ldapadd, ldapsearch

Backend storage: BerkeleyDB

Backend commands: slapadd, slapcat

Schemas: /etc/openldap/schema

Data: /var/lib/ldap


Configuration files

Client: /etc/openldap/ldap.conf

Server: /etc/openldap/slapd.conf
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Building an OpenLDAP Server
1. Install OpenLDAP.
2. Configure LDAP for your domain.
Change suffix, rootdn, rootpw options.
vim /etc/openldap/slapd.conf
3. Start server
Immediate: /sbin/service ldap start
Permanent: /sbin/chkconfig –level 35 ldap on
4. Add data with ldapadd
5. Verify functionality with ldapsearch
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LDAP Authentication
1. Configure server with schema + user data.
2. Point clients to hostname and rootDN of svr.
/etc/ldap.conf and
/etc/openldap/ldap.conf
3. Verify server access with ldapsearch
4. Configure clients to use LDAP auth
/etc/nsswitch.conf
passwd: files ldap
shadow: files ldap
group: files ldap
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References

1. Brian Arkills, LDAP Directories Explained: An Introduction and
Analysis, Addison-Wesley, 2003.
2. Gerald Carter, LDAP System Administration, O’Reilly, 2003.
3. J. Heiss, “Replacing NIS with Kerberos and LDAP,”
2004.
4. LDAP Howtos, Links, and Whitepapers,
2005.
5. 2005.
6. Luiz Malere, “Linux LDAP HOWTO,”
2004.
7. OpenLDAP, OpenLDAP Administrator’s Guide,
2005.
8. RedHat, Red Hat Enterprise Linux 4 Reference Guide, Chapter 13,
/>f-guide/
, 2005.