IETF67

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IETF67 Diameter TutorialDiameter Base
Protocol DetailsVictor Fajardo and Yoshihiro
OhbaToshiba America Research Inc.
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• 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

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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
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• 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

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Diameter - Message Format

• Diameter Message

Diameter Header
AVP
AVP
AVP
AVP Header
AVP Data
Version, Length, Flags, Code, AppId, H2H Id, E2E
Id
Diameter Header
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.)

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Diameter ABNF Example

• ltCERgt lt Diameter Header 257, REQ gt
• 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
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• Connection Management
• Peer Discovery
• Transport
• Capabilities negotiation
• Peer liveness and disconnection

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• 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

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• 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

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• 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

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• 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

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

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• 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

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• 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, RADIUSlt-gtDIAMETER
• Re-Direct Agents
• Does not forward messages but notifies the
  previous hop of the new next-hop to use
• Advertises support all applications

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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

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• 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

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• Request Routing (Contd)
• 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

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Routing Overview
SomeOtherRealm.com
1. Request (EAP, RealmB.com)
2. Request (EAP, Server.RealmB.com)
Relay/Proxy Agent
Diameter Server
Diameter Client
Request Queue
Request Queue
3. Answer
4. Answer
Server.RealmB.com
Client.RealmA.com
Relay.RealmB.com

• Example Realm Routing Table for Relay/Proxy
  Agent
• RealmB.com
• AppIdEAP, ActionPROXY, Next-HopServer.RealmB.co
  m, isStaticTRUE
• AppIdxxx, ActionRELAY, Next-HopServer.RealmB.co
  m, isStaticTRUE
• RealmA.com
• AppIdxxx, ActionRELAY, Next-HopClient.RealmA.co
  m, isStaticTRUE
• SomeOtherRealm.com
• AppIdEAP, ActionREDIRECT, Next-HopServer.RealmB
  .com, isStaticFALSE, ExpireTime3600

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• 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

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• 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

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• 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
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• 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

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• Session Management
• Diameter Sessions - definitions
• Session types and statefulness
• Authentication and Authorization Sessions
• Accounting Sessions

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• 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
• ltDiameterIdentitygtlthigh 32 bitsgtltlow 32
  bitsgtltoptional valuegt
• 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

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• 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

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• 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

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• Accounting Sessions
• Uses Base Protocol messages ACR/ACA
• Accounting Session State Machines
• CLIENT
• SERVER/STATELESS
• SERVER/STATEFUL

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• 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-Id sub-divides an accounting
  session
• Accounting-Realtime-Required AVP specifies
  realtime accounting behavior

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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

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• 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

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• 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 RADIUSlt-gtDiameter Translation Agents

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• Interoperability with RADIUS (Contd)
• 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 extended attributes to Diameter
  AVPs

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• 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

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End of Tutorial Thank You