Subject: Automatic Prefix Delegation draft

From: Brian Haberman <[email-masked]>
Date: Thu, 07 Mar 2002 07:56:32 -0500

All,
     Jim and I have updated the Automatic Prefix Delegation draft
to take into account comments and suggestions made in the last few
months.  I submitted it to the I-D editor last week, but have not
seen it posted yet so it is attached.  Comments and suggestions are
always welcome.

Brian

   Individual Submission                                       B. Haberman 
   Internet Draft                                                J. Martin 
   draft-haberman-ipngwg-auto-prefix-02.txt                                
   February 2002                                                           
   Expires August 2002                                                     

                Automatic Prefix Delegation Protocol for 
                   Internet Protocol Version 6 (IPv6) 
    
               <draft-haberman-ipngwg-auto-prefix-02.txt> 

Status of this Memo 
 
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026.  
    
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups. Note that 
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of 
   six months and may be updated, replaced, or obsoleted by other 
   documents at any time. It is inappropriate to use Internet- Drafts 
   as reference material or to cite them other than as "work in 
   progress."  
    
   The list of current Internet-Drafts can be accessed at 
   http://www.ietf.org/ietf/1id-abstracts.txt. 
     
   The list of Internet-Draft Shadow Directories can be accessed at 
   http://www.ietf.org/shadow.html. 

Abstract 
    
   The expansion of the IP address space provided by IPv6 makes it both 
   possible and reasonable to allocate entire subnets to environments 
   that had been previously limited to a few individual IP addresses. 
   Other protocols such as Neighbor Discovery and Stateless Address 
   Autoconfiguration allow hosts within those subnets to be 
   automatically configured. The router between this subnet and the 
   upstream world requires just one more piece to make this process 
   automatic, a network prefix. 
    
   This document describes a mechanism for the automated delegation of 
   an IPv6 network prefix. It allows routers to request either a 
   specific prefix or any prefix. Upon authorizing the request the 
   delegating router then returns a prefix and a lifetime for the use 
   of the prefix.  Optionally, the delegating and requesting routers 
   can exchange routing protocol information. 

Haberman, Martin                                                     1 
 

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
1. Introduction 
    
   This specification defines the Prefix Delegation (PD) protocol for 
   Internet Protocol Version 6 (IPv6). Routers use Prefix Delegation to 
   request a network prefix for use on directly attached networks.  
   Upon receipt of the request, the delegating router may authenticate 
   the request, and will establish if the requested prefix size is 
   acceptable. The delegating router then specifies the prefix for use 
   and the length of time for which that prefix is delegated. 
    
   The Prefix Delegation protocol supports extensible options.  These 
   options may be used to negotiate additional operational parameters, 
   such as routing protocol information. 

2. Terminology 
    
  2.1 General 
    
   This document uses the terminology defined in [RFC 2460] and [RFC 
   2461] and in addition: 
    
        - Requesting Router - The router that is requesting that a 
           prefix be assigned 
    
        - Delegating Router - The router that is responding to the 
           prefix request 
 
  2.2 Requirements 
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in 
   this document are to be interpreted as described in [RFC 2119]. 

3. Scope of Work 
    
   This proposal is meant to give a singly homed leaf router the 
   ability to obtain an IPv6 prefix that can be used within its leaf 
   network.  Future revisions of this document may support a more 
   generic approach to dynamic prefix delegation. 
    
   It is also assumed that the delegating server/router shares a 
   network connection with the requesting router.  Future revisions may 
   remove this restriction and allow for either multi-hop messages or a 
   relay function. 

4. Protocol Overview 

Haberman, Martin                                                     2 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
   The Prefix Delegation protocol defines two new ICMP message types, 
   the Prefix Request and the Prefix Delegation. The Prefix Request is 
   used by the Requesting Router to communicate requests to the 
   Delegating Router. Conversely, the Prefix Delegation is used by the 
   Delegating Router to communicate prefix and error information with 
   the Requesting Router. 
    
  4.1 Delegator Query 
    
   The Requesting Router begins the Prefix Delegation process by 
   sending a Prefix Request message of type [DELEGATOR QUERY] to the 
   All-Routers link-local multicast address (FF02::2).  
    
   Upon receipt of the Delegator query, a Delegating Router determines 
   if it is configured to provide prefixes of the specified scope. If 
   so, it unicasts a Prefix Delegation of type [PREFIX DELEGATOR] to 
   the Requestor. If not, the message is silently discarded. 
    
   After sending the query, the Requestor waits for Query Interval 
   (Default: 5) seconds for one or more Delegating Routers to respond. 
   If there is no response, the Delegator Query is sent again up to Max 
   Query times (Default: 3). If no response is received, there are no 
   Prefix Delegation services available, and Prefix Delegation has 
   failed. 
    
   If more than one response is received to the query within the Query 
   Interval, the response with the numerically highest source IP 
   address is used.  
 
  4.2 Initial Request 
    
   Once a Delegating Router is chosen, the Requestor sends a Prefix 
   Request message of type Initial Request to the unicast IP address of 
   the chosen Delegating Router. 
    
   The Requestor may or may not have a Security Association with the 
   Delegating Router, however if Authentication is required and no SA 
   is present, the Delegator will reject the request with an error 
   response indicating that Authentication is required. The Requestor 
   then builds a Security Association with the Delegator and sends 
   another Initial Request including the SA information. 
    
   If no response is heard within Request Timeout seconds (Default: 5), 
   the Initial Request should be sent again, up to Max Initial Request 
   (Default: 3) tries. If no response is heard, a Delegator Query is 
   sent and the process restarted. If this cycle is repeated Max 
   Delegation Attempts times (Default: 3), Prefix Delegation has 
   failed. 
    
  4.3 Message Security 

Haberman, Martin                                                     3 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
   Upon receipt of the Prefix Request of any type, the Delegating 
   Router establishes if there is a need for Authentication and/or 
   Encryption, based upon local policy. If either is required and none 
   is provided, the Delegator will return a Prefix Delegation message, 
   with a code of Authentication Required. 
 
   The building of a Security Association between the Delegator and the 
   Requestor is based on the Authentication and/or Encapsulated 
   Security Payload extension headers defined in [RFC 2402] and [RFC 
   2406].   
  
  4.4 Prefix Delegation 
    
   After the request is verified to be acceptable, the Delegating 
   Router allocates the requested prefix size from its pool of 
   available addresses. The creation and management of that pool is 
   beyond the scope of this document, but it can be supposed that 
   minimalistically a Delegating Router will be statically configured 
   with a fixed pool. If no acceptable prefix is available, a Prefix 
   Delegation message with a code of Prefix Unavailable is returned. 
 
   The Delegating Router then sends a Prefix Delegation message to the 
   Requesting Router containing a code of Prefix Delegation and all of 
   the prefix information.  The Requesting Router then activates the 
   prefix on its interface of choice. 
    
  4.5 Prefix Refresh 
    
   All Prefix Delegations have a lifetime that MUST follow the rules 
   defined in Section 4.6.2 of [RFC 2461].  Upon receiving a Prefix 
   Delegation, the requesting router initiates a timer such that before 
   the lifetime expires, the Requesting Router sends a Prefix Request 
   with code=REFRESH directly to the Delegating router. 
    
   If the Requestor receives no response within [RENEWAL TIMEOUT] 
   seconds (Default: 5), the Renewal Request should be sent again, up 
   to [MAX RENEWAL REQUEST] (Default: 3) tries.  If no response is 
   heard the previously allocated prefix is not renewed. 
    
   A Requesting Router receiving the Prefix Unavailable code, or no 
   response at all, has not had the prefix renewed.  It will expire at 
   the end of the initial lifetime.  To acquire a new prefix, the 
   Requesting Router must begin anew as described in Section 4.1. 
    
  4.6 Prefix Return 
    
   If the Requesting Router no longer requires the use of a prefix, it 
   can return that prefix to the control of the Delegating Router 
   through the use of the Prefix Return code in a Prefix Request. The 
   requesting router sends a Prefix Request directly to the Delegating 
   Router. 
  
Haberman, Martin                                                     4 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 

   Upon receipt and verification (if needed) of this message, the 
   Delegating Router returns the prefix to the pool and issues a Prefix 
   Delegation with a code of Prefix Returned. 
 
5. Messages 
 
   All messages have the following general format: 

      0                   1                   2                   3 
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     |     Type      |     Code      |          Checksum             | 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     |                                                               | 
     +                          Message Body                         + 
     |                                                               | 

   The following sections describe the specific messages and options 
   used in delegating IPv6 prefixes. 
 
  5.1 Prefix Request Message 
    
   The Prefix Request Message is sent to request, renew, or release a 
   prefix.   

   IP Fields 
     
      Source Address 
          An IP address assigned to the sending interface. 
           
      Destination Address 
          The All-Routers link-local multicast address (FF02::2)for 
          Delegator Query messages. All other Prefix Request messages 
          should be sent to a unicast address of the Delegating Router. 
           
      Authentication Header 
          If a Security Association for the IP Authentication Header 
          exists between the sender and the destination address, then 
          the sender SHOULD include this header. No such header is 
          required for the initial prefix request that is multicast, 
          but may be required for further progress. 
     
    ICMP Fields 
    
      Type 
          XXX (Where XXX is assigned by IANA) 

Haberman, Martin                                                     5 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
      Code 
          They Type of Request Code: 
    
          Delegator Query (0) 
                The Delegator Query is used by the Requestor to 
                identify potential Delegating Routers. It is sent to 
                the All-Routers link-local multicast address with no 
                Authentication Header. 
    
          Initial Request (1) 
                The Initial Request is used to initiate the request 
                process. It is sent to the unicast IP address of the 
                Delegating Router, and may carry an Authentication 
                Header. Unused fields MUST be set to zero.  An Initial 
                Request code MAY contain a Prefix Option. 
 
          Renewal Request (2) 
                The Renewal Request is used to renew a prefix that has 
                been previously allocated.  It is sent to a unicast IP 
                address of the Delegating Router and may carry an 
                Authentication Header.  A Renewal Request code MUST 
                contain at least one Prefix Option. 
                 
          Prefix Return (3) 
                The Prefix Return is used to return an unused prefix, 
                or portion of a prefix to the control of the Delegating 
                Router. It is sent to a unicast IP address of the 
                Delegating Router and may carry an Authentication 
                Header.  A Prefix Return code MUST contain at least one 
                Prefix Option. 
                 
      Checksum 
          The ICMP checksum as defined in [RFC 2463]. 
           
  5.2 Prefix Delegation Message Format 
    
   The Prefix Delegation Messages are sent to provide the addresses of 
   available Prefix Delegators, to provide prefix data, and for error 
   returns. 

   IP Fields 
     
      Source Address 
          An IP address assigned to the sending interface. 
           
      Destination Address 
          The IP address of the Requestor as specified by the IP Source 
          Address in the Prefix Request message. 
                         
      Authentication Header 

Haberman, Martin                                                     6 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
          If a Security Association for the IP Authentication Header 
          exists between the sender and the destination address, then 
          the sender SHOULD include this header. 
     
    ICMP Fields 
    
      Type 
          XXX+1 (Where XXX+1 is assigned by IANA) 
           
      Code 
          The Type of Response Code: 
    
          Prefix Delegator (0) 
                The Prefix Delegator is used by the Delegator to inform 
                the Requestor that it is available to provide prefixes 
                of the desired type. It is sent to the unicast IP 
                address in the Source Address portion of the Prefix 
                Request packet. Unused fields MUST be set to zero. 
    
          Authentication Required (1) 
                The Authentication Required message indicates to the 
                Requestor that a Security Association must be 
                established before a prefix can be delegated. It is 
                sent to the unicast IP address in the Source Address 
                portion of the Prefix Request packet. Unused fields 
                MUST be set to zero. 
                 
          Authorization Failed (2) 
                The Authorization Failed message indicates to the 
                Requestor that either it is not authorized to request a 
                prefix, or that the prefix requested fell outside of 
                local policy. It is sent to the unicast IP address in 
                the Source Address portion of the Prefix Request 
                packet. Unused fields MUST be set to zero. 
                 
          Prefix Unavailable (3) 
                The Prefix Unavailable indicates that the Prefix 
                Request was acceptable, but the Delegator does not have 
                sufficient available address space to fulfill the 
                request.  It is sent to the unicast IP address in the 
                Source Address portion of the Prefix Request packet.  
                Unused fields MUST be set to zero. 
                 
          Prefix Delegated (4) 
                The Prefix Delegated message actually provides the 
                prefix information that the Requestor has requested. It 
                is sent to the unicast IP address in the Source Address 
                portion of the Prefix Request packet. For this message, 
                a Prefix Option MUST be included. 
                 
          Prefix Returned (5) 

Haberman, Martin                                                     7 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 
    
                The Prefix Return is used to confirm the return of a 
                prefix. It is sent to the unicast IP address in the 
                Source Address portion of the Prefix Request packet. 
                For this message, the Prefix Option MUST be included. 
                                
      Checksum 
          The ICMP checksum. 
           
  5.3 Prefix Option 
    
   The Subnet Prefix Option is used to relay prefix information between 
   Requestors and Delegators.  It has the following format: 

      0                   1                   2                   3 
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     |     Type      |    Length     |          Reserved             | 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     |                        Prefix Lifetime                        | 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
     |                                                               | 
     +                                                               + 
     |                                                               | 
     +                             Prefix                            + 
     |                                                               | 
     +                                                               + 
     |                                                               | 
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

    Prefix Option Fields 
 
      Type = 0x01 
          This field identifies the presence of a subnet prefix.  This 
          option MUST follow either a Prefix Request header or a Prefix 
          Delegation header. 
     
      Length 
          The length of the prefix contained in the option. 
           
      Reserved 
          This field is unused. It MUST be initialized to zero by the 
          sender and MUST be ignored by the receiver. 
       
      Prefix Lifetime 
          The lifetime of the prefix contained in the option. 
 
      IPv6 Prefix 
          The Prefix field is used to carry a subnet prefix. The host 
          portion of the IP address MUST be padded with zeros. 

Haberman, Martin                                                     8 
    

 
Internet Draft      <Automatic Prefix Delegation>       February 2002 

6. Security Considerations 
    
   The ability to automate the delegation of prefixes opens several 
   security vulnerabilities.  Rogue delegators can issue bogus prefixes 
   to requestors.  This may cause denial of service due to 
   unreachability.  Rogue requestors may consume valuable resources 
   from legitimate delegators, thus denying others the use of the 
   prefixes.  For these reasons, the use of IPSec-based Authentication 
   and/or Encryption is suggested. 
    
7. To Do's 
    
   - Additional security discussion 
   - Relay functionality 
   - Routing capabilities option 
    
8. Acknowledgements 
    
   We would like to acknowledge and thank Jun-ichiro itojun Hagino, 
   Dave Thaler, Yamasaki Toshi, Ole Troan, and Kazuaki Tsuchiya for 
   their feedback and suggestions on this document. 
    
9. References

   [RFC 2460] S. Deering and R. Hinden, "Internet Protocol, Version 6 
              (IPv6) Specification", RFC 2460, December 1998. 
    
   [RFC 2461] T. Narten, E. Nordmark, and W. Simpson, "Neighbor 
              Discovery for IP Version 6 (IPv6)", RFC 2461, December 
              1998. 
    
   [RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate 
              Requirement Levels", RFC 2119, BCP 14, March 1997. 
    
   [RFC 2463] A. Conta and S. Deering, "Internet Control Message 
              Protocol (ICMPv6) for the Internet Protocol Version 6 
              (IPv6) Specification", RFC 2463, December 1998. 

Authors' Addresses 
    
   Brian Haberman 
   [email-masked] 
 
   Jim Martin 
   [email-masked] 

Haberman, Martin                                                     9