Transcript Using Exim with LDAP

Using Exim with LDAP
Douglas Gray Stephens
Senior Directory Architect
Schlumberger
Topics
• What is LDAP;
• What is LDAP designed for;
• How is LDAP integrated into Exim;
• Case study of using Exim with LDAP;
• How to trouble shoot Exim with LDAP;
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What is LDAP
• Light weight Directory Access Protocol;
• (X.500 is DAP, so more heavy weight);
• Communications protocol :
– no specification for back end server system;
• Standards based;
• Defacto standard for internet white pages (c.f.
http for on line documents).
• Current version is LDAPv3 (ratified in 2000)
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What is LDAP designed for
• Systems where there are few writes, but many
reads;
• Storing any data;
• Fast response for queries;
• Redundancy (i.e automatic fail over);
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What is LDAP not designed for
• It is not a relational database;
• Is not efficient for systems with frequent writes;
• Server may return unexpected (e.g. no) results if
attribute not indexed.
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How is data stored in LDAP (DIT)
• LDAP is a tree structure (Document Information Tree):
dc=com
dc=company1
ou=people
ou=pager
cn=Douglas Gray Stephens
cn=John Smith
cn=John Smith2
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dc=company2
ou=list
......
l=cambridge
l=houston.
l=london
LDAP searches
• Require
– Server to search (where to look);
– Search root (part of DIT to start searching from);
– Scope (how far to look ─ base, one level, or sub
tree);
– Filter (what to look for);
– Attribute(s) to return;
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LDAP search example
• E.g. ldapsearch –h myhost:389
–b dc=company1,dc=com
–s sub
“(cn=douglas gray stephens)”
cn sn givenname mail
– Returns
dn: cn=Douglas Gray
Stephens,ou=employee,dc=company1,dc=com
cn: Douglas Gray Stephens
cn: Douglas Gray-Stephens
cn: Grey Stevens
sn: Gray Stephens
givenName: Douglas
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mail: [email protected]
LDAP filters
• Components of filter nested within brackets
“(…..)”;
• Items can be ANDed together (with “&”);
• Items can be ORed together (with “|”);
• Items can be negated (with “!”);
• Searches can include wild cards (with “*”);
• RFC 2254 gives full details.
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LDAP filter example
• E.g.
“(&(mail=*)(c=gb)(!(l=london))(cn=douglas*))”
• Means
–
–
–
–
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Find all records with an mail attribute
that are in the United Kingdom (GB)
and are do not have London as the city
and have a common name starting with douglas
LDAP URLs
• An LDAP URL begins with the protocol prefix
"ldap" and is defined by the following grammar,
as defined in RFC 2255:
<ldapurl> ::= "ldap://" [ <host:port> ] "/" <dn> [ "?"
<attributes>
[ "?" <scope> "?" <filter> ] ]
<host:port> ::= <hostname> [ ":" <portnumber> ]
<dn> ::= a string as defined in RFC 2253
<attributes> ::= NULL | <attributelist>
<attributelist> ::= <attributetype>
| <attributetype> [ "," <attributelist> ]
<attributetype> ::= a string as defined in RFC 1777
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<filter> ::= a string as defined in RFC 2254
LDAP URL example
•
ldap://server1
server2:387/dc=com?cn,mail?sub?(&(cn=douglas*)(l=cambridge))
• Specifies that
– there are two servers to try (server1, then server2).
Note the second server is on a non standard port (387);
– a search root of “dc=com”;
– attributes “cn” and “mail” should be returned;
– the sub tree should be searched;
– using a filter “(&(cn=douglas*)(l=cambridge))”;
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Building Exim
• Requires that the LDAP libraries be available
– OpenLDAP (http://www.openldap.org/);
– SunOne (previously Netscape/iPlanet)
(http://www.sun.com/software/products/directory_s
rvr_ee/ )
• Specify in Makefile
LOOKUP_LDAP=yes
LDAP_LIB_TYPE=OPENLDAP1/OPENLDAP2/NETSCAPE/SOLAR
IS
LOOKUP_INCLUDE=-I /???/include
LOOKUP_LIBS=-L/???/lib -lldap -llber
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Configuring Exim
• Location of LDAP servers
ldap_default_servers = “\
localhost::389 : \
server1::389 : \
server2::387”
• Some router/transport commands to make use of
LDAP (use anywhere that you would use the
exim lookup functionality).
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LDAP lookups in Exim
• Types of lookups:
– ldap requires the result to contain just one entry;
if there are more, it gives an error.
– ldapdn also requires the result to contain just one
entry, but it is the Distinguished Name that is
returned rather than any attribute values.
– ldapm permits the result to contain more than one
entry;
the attributes from all of them are returned;
each entry in result string is on a separate line;
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LDAP lookup results
• ldap:///o=base?attr1?sub?(uid=frederic)
value1.1, value1.2
• ldap:///o=base?attr2?sub?(uid=frederic)
value two
• ldap:///o=base?attr1,attr2?sub?(uid=frederic)
attr1="value1.1, value1.2" attr2="value two"
• ldap:///o=base?objectclass,cn,sn?sub?(uid=frede
ric)
objectClass="top, person" cn=“Frederic Smith, Fred Smith"
sn=“Smith“
• ldapm:///o=base??sub?(uid=fred*)
objectClass="top,person" attr1="value1.1, value1.2" attr2="value
two“
objectClass="top,person" …. Etc. for the second match
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Case study
• Objective
– Look up names in LDAP and forward to
appropriate person;
– Handle instance when multiple matches;
– Handle instance when there is no email address;
– Enable user to control lookup options (so limiting
spam).
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Details of mail handling
• Addresses of the form [email protected] will
always be sent to only one person, since a uid is
by definition unique within the directory.;
• Addresses of the form [email protected] will be processed according
to the following rules.
–
–
–
–
–
–
–
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Forward to record that matches uid and has email address
Forward to record that matches the common name(s)
Forward to record that givename/surname
Forward to a record that contains all the words in the common name(s)
If record does not have email address, return phone number
If there are 2 to 5 matches, give more details to sender
If there are more than 5 matches, bounce message
Mail processing
• For a single match, the message is forwarded to
that address;
• For 2 to 5 matches, the message is bounced
back to the sender along with details of the
matches. The sender is asked to try again.
• For more than 5 matches, the message is
bounced back to the sender. The sender is asked
to be more specific about the address.
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Message flow
Loop through series of
LDAP lookups
Perl code alias_bounce
handles
• no matches
• 2 to 5 matches
• more than 5 matches
•No email address
(snail mail details)
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Zero or more than one
matches is failure for
ldapm lookup
Perl code ldap_one sets
new_address and status
Exim Global parameters
• ldap_default_servers = “server1 server2:387”
• What should be returned:
Perl function that builds up
LDAP_URL =
an LDAP filter
ldap:///dc=comany1,dc=com?uid,mail,cn,ou,telephonenumber,
o?sub?
• Search definitions for different lookups:
– MAIL_UID_MATCH = &(mail=*)(uid=${perl{punc_to_dash}{$local_part
– MAIL_CN_MATCH
= &(mail=*)(cn=${perl{punc_to_spc}{$local_part}})
– MAIL_GIVENNAME_SN_MATCH =
&(mail=*)(${perl{givenname_sn_match}{$local_part}})
– MAIL_CN_WORDS_MATCH =
&(mail=*)(${perl{cn_match}{$local_part}})
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LDAP router example
company1_user:
driver = redirect
Returns mail address when one match
allow_defer
allow_fail
condition = "${perl{ldap_who} \
{${lookup ldapm {LDAP_URL(MAIL_UID_MATCH)}{$value} \
{${lookup ldapm {LDAP_URL(MAIL_CN_MATCH)} {$value} \
{${lookup ldapm {LDAP_URL(MAIL_GIVENNAME_SN_MATCH)}
{$value} \
{${lookup ldapm {LDAP_URL(MAIL_CN_WORDS_MATCH)} {$value}
\
{DUNNO}}}}}}}}}}"
data = ${perl{new_address}}
domains = company1.com
headers_add = "X-LDAP-Alias: V LDAP_ALIAS_VERSION. Sent to
$local_part@$domain resolving to ${perl{new_address}}"
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Bounce router
unknownuser:
driver = accept
retry_use_local_part
transport = uid_bounce
no_verify
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Bounce transport
uid_bounce:
driver = autoreply
from = Comapny1 Mail Server <[email protected]>
headers = "X-LDAP-To: bouncing ${local_part}@${domain}
(${perl{failure_reason}})\n\
Mime-Version: 1.0\nContent-Type: multipart/mixed;
boundary=\"${perl{mime_boundary}}\""
log = "/var/spool/exim/log/bouncelog"
once = "/var/spool/exim/db/bounce/${local_part}"
once_repeat = 1w
return_message
subject = "Unable to deliver to ${local_part}@${domain}"
text = ${perl{mime_bounce}{${domain}}}
to = $sender_address
transport_filter = "/etc/exim/close_mime ${perl{mime_boundary}}"
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Sample too many matches
From: Company1 Mail Server <[email protected]>
Subject: Unable to deliver to [email protected]
……
To help you locate the correct individual, selected fields from the possible
matches are
included below. The uid field is the only onemguaranteed unique within a given
community.
Name
Uid
Email
Organisation
City
Name
Uid
Email
Organisation
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2005
: Andy Few
:
:
:
:
AFew1
[email protected]
Company1
london
: Alex Few
:
:
:
:
afew2
[email protected]
Company1
cambridge
Example with no email address
From: Company1 Mail Server <[email protected]>
Subject: Unable to deliver to [email protected]
Dear email sender,
This message has been automatically generated because I, the email server,
found a
single match looking for <[email protected]> but that match contained no
forwarding email address and was thus undeliverable. The details of this match
are as
follows:
Name
Uid
Organisation
City
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2005
: Dark Ages
:
:
:
:
dages1
Company1
Oxford
+44 1865 1234567
Trouble shooting
• Test out address resolution
– exim -bt [email protected]
[email protected]
<-- [email protected]
router = perimeter_routes, transport = remote_smtp
host mail-relay.slb.com [163.184.1.20]
host mail-relay.slb.com [134.32.26.55]
host mail-relay.slb.com [163.187.152.23]
host mail-relay.slb.com [163.188.150.130]
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Trouble shooting (cont)
• Additional debugging
exim -d+lookup -bt [email protected]
Shows details including LDAP calls
database lookup required for
……..
perform_ldap_search: ldapm URL =
"ldap:///dc=company1,dc=com?uid,mail,cn,ou,telephonenumber,o?sub?(&(mail=*)(ui
d=dgraystephens))" server=localhost port=389 sizelimit=0 timelimit=0 tcplimit=-1
after ldap_url_parse: host=localhost port=389
ldap_initialize with URL ldap://localhost:389/
……
ldap_parse_result yielded 0: Success
LDAP search: returning: cn="Douglas Gray Stephens, Douglas Gray-Stephens, Grey
Stevens" mail="[email protected]" o="Company1" ou="Core services"
uid="dgraystephens" telephoneNumber="44 1223 325295 “
Check LDAP server logs for connection details
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Controlling fuzzy logic or spam
• Fuzzy logic is good when there is no spam
• If spam is an issue, then enable users to opt in or
out
• Add new component to searches, e.g.
MAIL_CN_MATCH
=
&(mail=*)(cn=${perl{punc_to_spc}{$local_part}})
becomes
MAIL_CN_MATCH
=
&(mail=*)(cn=${perl{punc_to_spc}{$local_part}})(!(description=exclud
e:cn))
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