Service%20Location%20Protocol

1
Service Location Protocol

• By
• Team Qwerty
• Aparna Atmaram
• Venkatesh Babu

2
Agenda

• What is SLP?
• Protocol Overview
• SLP Message Format
• SLP Security
• SLP Implementation
• Conclusion
• Reference

3
SLP

• What is Service Discovery?
• Examples of Service Discovery Protocols
• SLP v1
• SLP v2
• Jini
• Universal Plug and Play (UPnP)
• Bluetooths SDP

4
SLP Actors

• User Agent (UA)
• SLP Client communicates with SA or DA to access
  services
• Service Agent (SA)
• Offers services directly or by registering with
  DA on behalf of application
• Directory Agent (DA)
• optional actor to which all services register
• DA can be discovered either by active or passive
  discovery

5
SLP Architecture

• Centralized server architecture
• Decentralized architecture

6
SLP Service Discovery without DA

• Figure 1 Service Discovery without DA
• Source http//www-128.ibm.com/developerworks/li
  nux/library/l-slp/

7
SLP Service Discovery with DA

• Figure 2 Service Discovery with DA
• Source http//www-128.ibm.com/developerworks/li
  nux/library/l-slp/

8
SLP Message (1)

• General Message Format
• ----------------------
  ----------
• Version Function
  Length
• ----------------------
  ----------
• OMUAF rsvd Dialect
  Language Code
• ----------------------
  ----------
• Char Encoding
  XID
• ----------------------
  ----------
• Figure 3 SLP General Message Format
• Source http//www.ietf.org/rfc/rfc2165.txt?numbe
  r2165

9
SLP Message (2)
Message Type Abbreviation Service
Registration SrvReg Service Deregister SrvDeReg
Service Acknowledge SrvAck Service
Request SrvRqst Service Reply SrvRply Service
Type Request SrvTypeRqst Service Type
Reply SrvTypeRply Attribute Request AttrRqst Att
ribute Reply AttrRply DA Advertisement DAAdvert
SA Advertisement SAAdvert

10
Service Registration Message

• SrvReg
• Message sent by SA's to DA's containing
  information about a service that is available
• Message Format
• ----------------------
  ----------
• Service Location header
  (function SrvReg)
  
• ----------------------
  ----------
• 
  
  
• \ ltURL-Entrygt
  
  \
• 
  
  
• ----------------------
  ----------
• Length of Attr List String
  ltattr-listgt
  
• ----------------------
  ----------
• 
  
  
• \ ltattr-listgt, Continued.
  
  \
• 
  
  
• ----------------------
  ----------
• (if present) Attribute Authentication
  Block ...
• ----------------------
  ----------
• Figure 4 Service Registration Message Format

11
Service Deregister Message

• SrvDeReg
• Message sent by SA's to inform DA's that a
  service is no longer available.
• Message Format
• ----------------------
  ----------
• Service Location header
  (function SrvDereg)
  
• ----------------------
  ----------
• length of URL
  URL
  
• ----------------------
  ----------
• 
  
  
• \ URL of Service to Deregister,
  contd.
  \
• 
  
  
• ----------------------
  ----------
• (if present) authentication
  block .....
• ----------------------
  ----------
• length of lttag specgt string
  lttag specgt
• ----------------------
  ----------
• 
  
  
• \ lttag specgt, continued
  
  \
• 
  
  

12
Service Acknowledgement Message

• SrvAck
• A generic acknowledgment that is sent by DA's to
  SA's in response to SrvReg and SrvDeReg messages
• Message Format
• ------------------------
  --------
• Service Location header
  (function SrvAck)
• ----------------------
  ----------
• Error Code
  
  
• ----------------------
  ----------
• Figure 6 Service Acknowledgment Message Format
  
• Source http//www.ietf.org/rfc/rfc2165.txt?numb
  er2165

13
Service Request Message

• SrvRqst
• Message sent by UA's to SA's and DA's to request
  the location of a service
• Message Format
• ----------------------
  ----------
• Service Location header (function
  SrvReq)
  
• ----------------------
  ----------
• length of prev resp list stringltPrevious
  Responders Addr Specgt
• ----------------------
  ----------
• 
  
  
• \ ltPrevious Responders Addr
  Specgt
  \
• 
  
  
• ----------------------
  ----------
• length of predicate string Service
  Request ltpredicategt
• ----------------------
  ----------
• 
  
  
• \ Service Request ltpredicategt,
  contd.
  \
• 
  
  
• ----------------------
  ----------
• Figure 7 Service Request Message Format

14
Service Reply Message

• SrvRply
• Message sent by SA's and DA's in response to a
  SrvRqst message. The SrvRply contains the URL of
  the requested service
• Message Format
• ------------------------
  --------
• Service Location header (function
  SrvRply)
• ----------------------
  ----------
• Error Code
  URL Entry count
  
• ----------------------
  ----------
• ltURL Entry 1gt ...
• ----------------------
  ----------
• .
  
  
• \ .
  
  \
• .
  
  
• ----------------------
  ----------
• ltURL Entry Ngt ...
• ----------------------
  ----------
• Figure 8 Service Reply Message Format
• Source http//www.ietf.org/rfc/rfc2165.txt?numb
  er2165

15
SLP Security

• Security Considerations
• Authentication using Digital Signatures
• Authentication Block
• Signature Generation
• Signature Verification
• Protocol Vulnerability
• Relay Attacks
• Denial of Service Attacks

16
SLP Defining Service

• A service in SLP is defined by a service URL.
• The URL has the form
• serviceltservice-typegt//ltaddrspecgt
• ltservice-typegt is the type of service being
  advertised
• ltaddrspecgt is the service's location (domain
  name or IP address and port number).
• For example servicemail//mail.com25
• Above URL advertises a mail server at mail.com on
  port 25

17
OpenSLP APIs (1)

• SLP implementation is available with source at
  http//www.openslp.org/
• OpenSLP API is just an implementation of a
  standardized specification described in RFC 2614.
  
• The SLP API is a library interface that allows
  programmers to use SLP in their applications to
  locate services
• Following are the list of major APIs provided
• SLPReg()
• SLPDeReg()
• SLPFindSrvs()
• SLPFindAttrs()
• SLPFindSrvTypes()
• SLPParseSrvURL()

18
OpenSLP APIs (2)

• SLPOpen() Functions used to open SLPHandles
• SLPReg() Registers a service URL and service
  attributes with SLP.
• SLPDeReg() Deregisters a previously registered
  service.
• SLPFindSrvs() Finds services based on service
  type or attributes.
• SLPFindAttrs() Obtains a list of attributes for
  services registered with SLP.
• SLPFindSrvTypes() Obtains a list of the types
  of services that have been registered with SLP.  
• SLPParseSrvURL() Parses a Service URL passed in
  as a character string and returns the results in
  a pointer to a dynamically allocated SLPSrvURL
  structure.

19
Sample Application

1. Listing of SLP-enabled daytime server
   (Synchronous execution of SLP callback
   functions)
2. Listing of SLP-enabled daytime client

20
Conclusion

• SLP enables automatic service discovery and
  configuration of services over a network.
• Automatic service discovery is very advantageous
  given the mobility of today's computers.

21
References

• 1 RFC 2165. http//www.ietf.org/rfc/rfc2165.txt?
  number2165
• 2 Automate client management with the Service
  Location Protocol by M. Tim Jones.
  http//www-128.ibm.com/developerworks/linux/librar
  y/l-slp/
• 3 Service Location Protocol. http//www.redbooks
  .ibm.com/abstracts/TIPS0269.html?Open
• 4 Some Notes on Security in the Service
  Location Protocol Version 2 by Marco Vettorello,
  Christian Bettstetter, and Christian
  Schwingenschlogl. http//www.scs.carleton.ca/bar
  beau/wadhc/Papers/vettorello.pdf
• 5 OpenSLP API information from
  http//www.openslp.org/
• 6 OpenSLP API info from RFC 2614