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Tutorial Outline Diameter – Basic Functionality Message Format Protocol Details

IETF67 – Diameter Tutorial Diameter Base Protocol Details Victor Fajardo and Yoshihiro Ohba Toshiba America Research Inc. Tutorial Outline Diameter – Basic Functionality Message Format Protocol Details Connection Management Routing Session Management Creating new applications

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Tutorial Outline Diameter – Basic Functionality Message Format Protocol Details

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  1. IETF67 – Diameter TutorialDiameter Base Protocol DetailsVictor Fajardo and Yoshihiro OhbaToshiba America Research Inc. Diameter Tutorial - IETF67

  2. Tutorial Outline • Diameter – Basic Functionality • Message Format • Protocol Details • Connection Management • Routing • Session Management • Creating new applications • Improvements over Basic RADIUS • Interoperability with RADIUS • Recent Topics Diameter Tutorial - IETF67

  3. Diameter - Basic Functionality Diameter Client Node at somerealm.com Diameter Server Node at otherrealm.com Diameter Client Application Diameter Server Application Session Management Session Management Routing Management Routing Management Connection Management Connection Management Base Protocol Base Protocol Diameter Tutorial - IETF67

  4. Diameter - Basic Functionality • Base Protocol • Connectivity: Peering and Routing • Application support: Application session management • Applications • Purpose specific: NASREQ, MIPv4, SIP etc. • Identified by application Id • Every application MUST have an IANA-assigned application identifier • Used also for diameter message routing Diameter Tutorial - IETF67

  5. Diameter - Message Format • Diameter Message: Diameter Header AVP AVP AVP AVP Header AVP Data Diameter Header = Version, Length, Flags, Code, AppId, H2H Id, E2E Id Code, Flag, Length, Vendor-Id (Opt) AVP Header = • Each message must be defined using an ABNF grammar • Pre-defined AVP data types (Integer32, Float, OctetString etc.) Diameter Tutorial - IETF67

  6. Diameter ABNF Example <CER> ::= < Diameter Header: 257, REQ > { Origin-Host }/* Required AVP, Occurrence: 1 */ { Origin-Realm } 1* { Host-IP-Address }/* Required AVP, Occurrence: 1+ */ { Vendor-Id } { Product-Name } [ Origin-State-Id ]/* Optional AVP, Occurrence: 0 or 1 */ * [ Supported-Vendor-Id ]/* Optional AVP, Occurrence: 0+ */ * [ Auth-Application-Id ] * [ Inband-Security-Id ] * [ Acct-Application-Id ] * [ Vendor-Specific-Application-Id ] [ Firmware-Revision ] * [ AVP ] Note: /* */ is not part of ABNF Diameter Tutorial - IETF67

  7. Connection Management • Peer Discovery • Transport • Capabilities negotiation • Peer liveness and disconnection Diameter Tutorial - IETF67

  8. Peer Discovery • Peer discovery mechanisms (in order of preference) • Static configuration: mandatory • SLPv2 and DNS: optional • DNS mechanisms to use (in order of execution) • NAPTR • Address records for destination address ‘_diameter._sctp’.realm or ‘_diameter._tcp’.realm • Authorization of discovered peer is mandatory Diameter Tutorial - IETF67

  9. Transport • Protocols • Certain nodes MUST support at least SCTP or TCP (i.e. Diameter Client) • Others MUST support SCTP and TCP (i.e. Diameter Servers and Agents) • Security • TLS and IPSec • Selection Process (in order of execution) • IPSec, SCTP, TCP, TLS • SCTP or TCP is always attempted prior to capabilities exchange • TLS tried after capability negotiation • IPSec and TLS maybe used exclusively Diameter Tutorial - IETF67

  10. Capabilities Negotiation • Capabilities Exchange • Use of Capabilities-Exchange (CER/CEA) messages • Message exchange advertises: • Supported applications • Peer Identity • Security schemes – Indicates the use of TLS • SCTP host addresses if used • CER/CEA may or may not be protected • Peer Table Creation • Lists all peers that passes capabilities negotiation • Indicates the connection status of each peers • Also used for message routing Diameter Tutorial - IETF67

  11. Peer Liveness and Disconnection • Liveness Test • Use of Device-Watchdog exchange (DWR/DWA) • Aid in Failover performance: pro-active detection of failure • Disconnection • Use of Disconnect-Peer exchange (DPR/DPA) • Provides hints for future reconnection attempts • Routing and peer table updates Diameter Tutorial - IETF67

  12. Routing • Types of Diameter Nodes • Request Routing • Realm Routing Table • Answer Routing • Loop Detection • Failover-Failback Procedure • Duplicate Detection Diameter Tutorial - IETF67

  13. Types of Diameter Nodes • Diameter Clients and Severs • Request and Answer Originators • Where application normally reside • Advertises supported applications only • Diameter Agents • Request and Answer forwarders • Adds routing information to the message (Route-Record AVP) • Relay Agents • Provides basic message forwarding • Does not inspect content of the message other than Destination-Host and/or Realm and AppIds • Advertises support all applications Diameter Tutorial - IETF67

  14. Types of Diameter Nodes • Proxy Agents • Inspects and possibly modifies contents of the request or answer it is forwarding. • Useful in scenarios such policy enforcement, admission control, provisioning etc • Can maintain session state • Examples: Translation agents, RADIUS<->DIAMETER • Re-Direct Agents • Does not forward messages but notifies the previous hop of the new next-hop to use • Advertises support all applications Diameter Tutorial - IETF67

  15. Diameter Agent Overview Redirect Agent Redirect.RealmB.com 2. Request 3. Redirect Notification 1. Request 4. Request Client Relay/Proxy Agent Server 5. Answer 6. Answer Server.RealmB.com Client.RealmA.com • Request/Answer Path: • Normal Relay or Proxy: 1, 4, 5, 6 • Re-directed Agent: 1, 2, 3, 4, 5, 6 Diameter Tutorial - IETF67

  16. Request Routing • Information used for routing: • Application-Id: present is in the header • Destination-Host OR Destination-Realm AVP • Routing rules: • If local identity == Destination-Host AVP then process locally, otherwise • If peer identity == Destination-Host AVP then send that peer, otherwise (use Peer Table) • Lookup realm table with Destination-Realm and AppId • If found send to the designated next-hop • Otherwise, send an UNABLE_TO_DELIVER answer • Use of Request Queue • Successfully forwarded request are queued Diameter Tutorial - IETF67

  17. Request Routing (Cont’d) • Realm Routing Table • List of realm routing entries • Realm routing entry looks like: Realm (*), AppId (**), Action, Next-hop Peer, isStatic, ExpireTime • Realm: Primary key, matched with Destination-Realm Avp • AppId: Secondary key, matched with AppId in message header • Action: For each matching entry, possible actions are: • LOCAL, RELAY, PROXY, REDIRECT • isStatic: Indication of static or dynamic route • ExpireTime: Time before dynamic route are no longer valid Diameter Tutorial - IETF67

  18. Routing Overview SomeOtherRealm.com 1. Request (EAP, RealmB.com) 2. Request (EAP, Server.RealmB.com) Diameter Client Relay/Proxy Agent Diameter Server Request Queue Request Queue 4. Answer 3. Answer Server.RealmB.com Client.RealmA.com Relay.RealmB.com • Example Realm Routing Table for Relay/Proxy Agent: • RealmB.com • AppId=EAP, Action=PROXY, Next-Hop=Server.RealmB.com, isStatic=TRUE • AppId=xxx, Action=RELAY, Next-Hop=Server.RealmB.com, isStatic=TRUE • RealmA.com • AppId=xxx, Action=RELAY, Next-Hop=Client.RealmA.com, isStatic=TRUE • SomeOtherRealm.com • AppId=EAP, Action=REDIRECT, Next-Hop=Server.RealmB.com, isStatic=FALSE, ExpireTime=3600 Diameter Tutorial - IETF67

  19. Answer Routing • Information used for routing • Hop-by-Hop Id is used instead of Destination-Host or Destination-Realm AVP • Hop-by-Hop Id is unique within each hop • Answer routing path is the reverse of the request path • Routing Rules: • For answer originators: • Use the same Hop-by-Hop Id found in the request • For answer forwarders: • Lookup Hop-by-Hop Id in request queue • If found, forward answer to appropriate peer and remove request from the queue • Otherwise, discard Diameter Tutorial - IETF67

  20. Loop Detection • Recording the Routing Path • Forwarding agents add Route-Record AVPs • Detection • Local host identity must not be present in the Route-Record AVP • Send LOOP_DETECTED answer Diameter Tutorial - IETF67

  21. Failover-Failback Procedure • Failover: Attempt to re-route pending request to an alternate peer in case of transport failure • ‘T’ bit is set for re-routed requests • Failback: Switch back to the original next hop when connection is re-established Relay2 3. Request T-bit set Request Queue 4. Answer 2. Request T-bit set Server 5. Answer 1. Request 2. Request Client Relay1 Request Queue Request Queue 3. Answer 4. Answer Diameter Tutorial - IETF67

  22. Duplicate Detection • Duplicates can occur • Due to Failover • Nodes re-sending un-answered requests: Due to reboot • Detection • End-to-End Id is unique for a node • Re-sent request must have T-flag set • Therefore, use T-flag as a hint for possible duplication, then • Use End-to-End Id and Origin-Host AVP to detect duplication • Duplicate request SHOULD cause the same answer to be sent • Other Considerations • Use of Session-Id for duplicate detection in accounting records • Time needed to wait for duplicate messages Diameter Tutorial - IETF67

  23. Session Management • Diameter Sessions - definitions • Session types and statefulness • Authentication and Authorization Sessions • Accounting Sessions Diameter Tutorial - IETF67

  24. Diameter Sessions – definitions • What is a session? • A session is a related progression of events devoted to a particular activity • Applications provide guidelines as to when a session begins and ends • Sessions are identified by Session-Id • Globally and eternally unique <DiameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>] • DiameterIdentity: Senders identity in FQDN • High and Low 32 bits: Decimal representation of a 64-bit value, monotonically increased • Optional value: Implementation specific, i.e. MAC address, timestamp etc Diameter Tutorial - IETF67

  25. Session types and statefulness • Two types of sessions by usage • Authorization session is used for authentication and/or authorization • Accounting session is used for accounting • A session can be stateful or stateless • Depending on whether the application requires the session to be maintained for a certain duration • Stateful sessions normally spans multiple message exchanges Diameter Tutorial - IETF67

  26. Authentication and Authorization Sessions • Auth-Session-State indicates statefulness • For stateful session • Session teardown uses Base Protocol messages ASR/ASA and STR/STA • Support for Server-Initiated Re-Auth • Uses Base Protocol message RAR/RAA • Authorization Session State Machines: • CLIENT/STATELESS • CLIENT/STATEFUL • SERVER/STATELESS • SERVER/STATEFUL Diameter Tutorial - IETF67

  27. Accounting Sessions • Uses Base Protocol messages ACR/ACA • Accounting Session State Machines: • CLIENT • SERVER/STATELESS • SERVER/STATEFUL Diameter Tutorial - IETF67

  28. Accounting-related AVPs • Accounting-Record-Type AVP indicates type of accounting record: • Acct-Interim-Interval AVP specifies how and when to generate accounting records • Accounting-Record-Number AVP identifies an accounting record • Acct-Session-Id AVP is used for RADIUS/Diameter translation • Acct-Multi-Session-Id AVP co-relates multiple accounting sessions • Acct-Sub-Session-Idsub-divides an accounting session • Accounting-Realtime-Required AVP specifies realtime accounting behavior Diameter Tutorial - IETF67

  29. Creating a new application • Criteria: “New application is unable to fit within an existing application without requiring major changes to the specification” • Example major changes: • Adding new “mandatory-to-support” AVPs • A command requires different round trips than what is currently in the specification • Support for a new authentication method with new AVPs • As a last resort • Advocates reuse of existing applications and AVPs Diameter Tutorial - IETF67

  30. Improvements over Basic RADIUS • Features inherently offered by diameter • Reliable and secure transport • Failover • Agent support • Server-initiated messages • Capabilities negotiation • Peer discovery and configuration • RADIUS Extensions developed in RADEXT WG also provides most of these functionality, such as RFC3576 Diameter Tutorial - IETF67

  31. Interoperability with RADIUS • Diameter is upwards compatible with RADIUS, so • Messages and AVPs • AVP codes 1-255 is reused from RADIUS • Command codes 0-255 is reused from RADIUS • Diameter NASREQ (RFC4005) maps RADIUS messages to/from Diameter AA-Request and AA-Answer message • Use of RADIUS<->Diameter Translation Agents Diameter Tutorial - IETF67

  32. Interoperability with RADIUS (Cont’d) • Translations issues (to be resolved?) • Diameter MTU is larger than RADIUS MTU • Maximum Diameter AVP size is larger than maximum RADIUS attribute size • Mapping of RADIUS extendedattributes to Diameter AVPs Diameter Tutorial - IETF67

  33. Recent topics under discussion • Usage of Nas-Port-Type and Service-Type vs. defining a new Application Id • Use of zero(0) AppId for all base protocol messages • Explicit Routing Diameter Tutorial - IETF67

  34. End of Tutorial Thank You Diameter Tutorial - IETF67

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