+---------------------+-------------------+-----------------------+
| NAI realm (RADIUS)  | NAIRealm (cert)   | MATCH?                |
+---------------------+-------------------+-----------------------+
| foo.example         | foo.example       | YES                   |
| foo.example         | *.example         | YES                   |
| bar.foo.example     | *.example         | NO                    |
| bar.foo.example     | *ar.foo.example   | NO (NAIRealm invalid) |
| bar.foo.example     | bar.*.example     | NO (NAIRealm invalid) |
| bar.foo.example     | *.*.example       | NO (NAIRealm invalid) |
| sub.bar.foo.example | *.*.example       | NO (NAIRealm invalid) |
| sub.bar.foo.example | *.bar.foo.example | YES                   |
+-----------------+-----------------------------------------------+

Figure 4: Examples for NAI realm vs. certificate matching

Examples:

Appendix A contains the ASN.1 definition of the above objects.

3. DNS-based NAPTR/SRV Peer Discovery

3.1. Applicability

Dynamic server discovery as defined in this document is only applicable for new AAA transactions and per service (i.e. distinct discovery is needed for Authentication, Accounting, and Dynamic Authorization) where a RADIUS entity which acts as a forwarding server for one or more realms receives a request with a realm for which it is not authoritative, and which no explicit next hop is configured. It is only applicable for

1. new user sessions, i.e. for the initial Access-Request. Subsequent messages concerning this session, for example Access-Challenges and Access-Accepts use the previously-established communication channel between client and server.
2. the first accounting ticket for a user session
3. the first RADIUS DynAuth packet for a user session

3.2. Configuration Variables

The algorithm contains various variables for timeouts. These variables are named here and reasonable default values are provided. Implementations wishing to deviate from these defaults should make they understand the implications of changes.

• DNS_TIMEOUT: maximum amount of time to wait for the complete set of all DNS queries to complete: Default = 3 seconds
• MIN_EFF_TTL: minimum DNS TTL of discovered targets: Default = 60 seconds
• BACKOFF_TIME: if no conclusive DNS response was retrieved after DNS_TIMEOUT, do not attempt dynamic discovery before BACKOFF_TIME has elapsed. Default = 600 seconds

3.3. Terms

Positive DNS response: a response which contains the RR that was queried for.

Negative DNS response: a response which does not contain the RR that was queried for, but contains an SOA record along with a TTL indicating cache duration for this negative result.

DNS Error: Where the algorithm states "name resolution returns with an error", this shall mean that either the DNS request timed out, or a DNS response which is neither a positive nor a negative response (e.g. SERVFAIL).

Effective TTL: The validity period for discovered RADIUS/TLS target hosts. Calculated as: Effective TTL (set of DNS TTL values) = max { MIN_EFF_TTL, min { DNS TTL values } }

SRV lookup: for the purpose of this specification, SRV lookup procedures are defined as per [RFC2782], but excluding that RFCs "A" fallback as defined in its section "Usage Rules", final "else" clause.

Greedy result evaluation: The NAPTR to SRV/A/AAAA resolution may lead to a tree of results, whose leafs are the IP addresses to contact. The branches of the tree are ordered according to their order/preference DNS properties. An implementation is executing greedy result evaluation if it uses a depth-first search in the tree along the highest order results, attempts to connect to the corresponding resulting IP addresses, and only backtracks to other branches if the higher ordered results did not end in successful connection attempts.

3.4. Realm to RADIUS server resolution algorithm

3.4.1. Input

For RADIUS Authentication and RADIUS Accounting server discovery, input I to the algorithm is the RADIUS User-Name attribute with content of the form "user@realm"; the literal @ sign being the separator between a local user identifier within a realm and its realm. The use of multiple literal @ signs in a User-Name is strongly discouraged; but if present, the last @ sign is to be considered the separator. All previous instances of the @ sign are to be considered part of the local user identifier.

For RADIUS DynAuth Server discovery, input I to the algorithm is the domain name of the operator of a RADIUS realm as was communicated during user authentication using the Operator-Name attribute ([RFC5580], section 4.1). Only Operator-Name values with the namespace "1" are supported by this algorithm - the input to the algorithm is the actual domain name, preceeded with an "@" (but without the "1" namespace identifier byte of that attribute).

Note well: The attribute User-Name is defined to contain UTF-8 text. In practice, the content may or may not be UTF-8. Even if UTF-8, it may or may not map to a domain name in the realm part. Implementors MUST take possible conversion error paths into consideration when parsing incoming User-Name attributes. This document describes server discovery only for well-formed realms mapping to DNS domain names in UTF-8 encoding. The result of all other possible contents of User-Name is unspecified; this includes, but is not limited to:

• Usage of separators other than @
• Encoding of User-Name in local encodings
• UTF-8 realms which fail the conversion rules as per [RFC5891]
• UTF-8 realms which end with a . ("dot") character.

For the last bullet point, "trailing dot", special precautions should be taken to avoid problems when resolving servers with the algorithm below: they may resolve to a RADIUS server even if the peer RADIUS server only is configured to handle the realm without the trailing dot. If that RADIUS server again uses NAI discovery to determine the authoritative server, the server will forward the request to localhost, resulting in a tight endless loop.

3.4.2. Output

Output O of the algorithm is a two-tuple consisting of: O-1) a set of tuples {hostname; port; protocol; order/preference; Effective TTL} - the set can be empty; and O-2) an integer: if the set in the first part of the tuple is empty, the integer contains the Effective TTL for backoff timeout, if the set is not empty, the integer is set to 0 (and not used).

3.4.3. Algorithm

The algorithm to determine the RADIUS server to contact is as follows:

1. Determine P = (position of last "@" character) in I.
2. generate R = (substring from P+1 to end of I)
3. modify R according to agreed consortium procedures if applicable
4. convert R to a representation usable by the name resolution library if needed
5. Initialize TIMER = 0; start TIMER. If TIMER reaches DNS_TIMEOUT, continue at step 20.
6. Using the host's name resolution library, perform a NAPTR query for R (see "Delay considerations" below). If the result is a negative DNS response, O-2 = Effective TTL ( TTL value of the SOA record ) and continue at step 13. If name resolution returns with error, O-1 = { empty set }, O-2 = BACKOFF_TIME and terminate.
7. Extract NAPTR records with service tag "aaa+auth", "aaa+acct", "aaa+dynauth" as appropriate. Keep note of the protocol tag and remaining TTL of each of the discovered NAPTR records.
8. If no records found, continue at step 13.
9. For the extracted NAPTRs, perform successive resolution as defined in [RFC3958], section 2.2. An implementation MAY use greedy result evaluation according to the NAPTR order/preference fields (i.e. can execute the subsequent steps of this algorithm for the highest-order entry in the set of results, and only lookup the remainder of the set if necessary).
10. If the set of hostnames is empty, O-1 = { empty set }, O-2 = BACKOFF_TIME and terminate.
11. O' = (set of {hostname; port; protocol; order/preference; Effective TTL ( all DNS TTLs that led to this hostname ) } for all terminal lookup results).
12. Proceed with step 18.
13. Generate R' = (prefix R with "_radiustls._tcp." and/or "_radiustls._udp.")
14. Using the host's name resolution library, perform SRV lookup with R' as label (see "Delay considerations" below).
15. If name resolution returns with error, O-1 = { empty set }, O-2 = BACKOFF_TIME and terminate.
16. If the result is a negative DNS response, O-1 = { empty set }, O-2 = min { O-2, Effective TTL ( TTL value of the SOA record ) } and terminate.
17. O' = (set of {hostname; port; protocol; order/preference; Effective TTL ( all DNS TTLs that led to this result ) } for all hostnames).
18. Generate O-1 by resolving hostnames in O' into corresponding A and/or AAAA addresses: O-1 = (set of {IP address; port; protocol; order/preference; Effective TTL ( all DNS TTLs that led to this result ) } for all hostnames ), O-2 = 0.
19. For each element in O-1, test if the original request which triggered dynamic discovery was received on {IP address; port}. If yes, O-1 = { empty set }, O-2 = BACKOFF_TIME, log error, Terminate (see next section for a rationale). If no, O is the result of dynamic discovery. Terminate.
20. O-1 = { empty set }, O-2 = BACKOFF_TIME, log error, Terminate.

3.4.4. Validity of results

The dynamic discovery algorithm is used by servers which do not have sufficient configuration information to process an incoming request on their own. If the discovery algorithm result contains the server's own listening address (IP address and port), then this will either lead to a tight loop (if that DNS entry has topmost priority, the server would forward the request to itself, triggering dynamic discovery again in a perpetual loop), or lead to a potential loop with intermediate hops in between (the server could forward to another host with a higher priority, which might use DNS itself and forward the packet back to the first server). The underlying reason that enables these loops is that the server executing the discovery algorithm is seriously misconfigured in that it does not recognise the request as one that is to be processed by itself. RADIUS has no built-in loop detection, so any such loops would remain undetected. So, if step 18 of the algorithm discovers such a possible-loop situation, the algorithm should be aborted and an error logged. Note that this safeguard does not provide perfect protection against routing loops: other reasons include the possiblity that a subsequent hop has a statically configured next-hop which leads to an earlier host in the loop; or the algorithm execution was executed with greedy result evaluation, and the own address was in a lower-priority branch of the result set which was not retrieved from DNS at all.

After executing the above algorithm, the RADIUS server establishes a connection to a home server from the result set. This connection can potentially remain open for an indefinite amount of time. This conflicts with the possibility of changing device and network configurations on the receiving end. Typically, TTL values for records in the name resolution system are used to indicate how long it is safe to rely on the results of the name resolution. If these TTLs are very low, thrashing of connections becomes possible; the Effective TTL mitigates that risk. When a connection is open and the smallest of the Effective TTL value which was learned during discovering the server has not expired, subsequent new user sessions for the realm which corresponds to that open connection SHOULD re-use the existing connection and SHOULD NOT re-execute the dynamic discovery algorithm nor open a new connection. To allow for a change of configuration, a RADIUS server SHOULD re-execute the dynamic discovery algorithm after the Effective TTL that is associated with this connection has expired. The server MAY keep the session open during this re-assessment to avoid closure and immediate re-opening of the connection should the result not have changed.

Should the algorithm above terminate with O-1 = empty set, the RADIUS server SHOULD NOT attempt another execution of this algorithm for the same target realm before the timeout O-2 has passed.

3.4.5. Delay considerations

The host's name resolution library may need to contact outside entities to perform the name resolution (e.g. authoritative name servers for a domain), and since the NAI discovery algorithm is based on uncontrollable user input, the destination of the lookups is out of control of the server that performs NAI discovery. If such outside entities are misconfigured or unreachable, the algorithm above may need an unacceptably long time to terminate. Many RADIUS implementations time out after five seconds of delay between Request and Response. It is not useful to wait until the host name resolution library signals a time-out of its name resolution algorithms. The algorithm therefore control execution time with TIMER. Execution of the NAI discovery algorithm SHOULD be non-blocking (i.e. allow other requests to be processed in parallel to the execution of the algorithm).

3.4.6. Example

Assume

• a user from the Technical University of Munich, Germany, has a RADIUS User-Name of "foobar@tu-m[U+00FC]nchen.example".
• The name resolution library on the RADIUS forwarding server does not have the realm tu-m[U+00FC]nchen.example in its forwarding configuration, but uses DNS for name resolution and has configured the use of Dynamic Discovery to discover RADIUS servers.
• It is IPv6-enabled and prefers AAAA records over A records.
• It is listening for incoming RADIUS/TLS requests on 192.0.2.1, TCP/2083.

May the configuration variables be

• DNS_TIMEOUT = 3 seconds
• MIN_EFF_TTL = 60 seconds
• BACKOFF_TIME = 3600 seconds

If DNS contains the following records:

• xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" "" _myradius._tcp.xn--tu-mnchen-t9a.example.
• xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "fooservice:bar.dccp" "" _abc123._def.xn--tu-mnchen-t9a.example.
• _myradius._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083 radsecserver.xn--tu-mnchen-t9a.example.
• _myradius._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083 backupserver.xn--tu-mnchen-t9a.example.
• radsecserver.xn--tu-mnchen-t9a.example. IN AAAA 2001:0DB8::202:44ff:fe0a:f704
• radsecserver.xn--tu-mnchen-t9a.example. IN A 192.0.2.3
• backupserver.xn--tu-mnchen-t9a.example. IN A 192.0.2.7

Then the algorithm executes as follows, with I = "foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling in use:

1. P = 7
2. R = "tu-m[U+00FC]nchen.example"
3. NOOP
4. name resolution library converts R to xn--tu-mnchen-t9a.example
5. TIMER starts.
6. Result:
   • (TTL = 47) 50 50 "s" "aaa+auth:radius.tls" "" _myradius._tcp.xn--tu-mnchen-t9a.example.
   • (TTL = 522) 50 50 "s" "fooservice:bar.dccp" "" _abc123._def.xn--tu-mnchen-t9a.example.
7. Result:
   • (TTL = 47) 50 50 "s" "aaa+auth:radius.tls" "" _myradius._tcp.xn--tu-mnchen-t9a.example.
8. NOOP
9. Successive resolution performs SRV query for label _myradius._tcp.xn--tu-mnchen-t9a.example, which results in
   • (TTL 499) 0 10 2083 radsec.xn--tu-mnchen-t9a.example.
   • (TTL 2200) 0 20 2083 backup.xn--tu-mnchen-t9a.example.
10. NOOP
11. O' = {
    • (radsec.xn--tu-mnchen-t9a.example.; 2083; RADIUS/TLS; 10; 60),
    • (backup.xn--tu-mnchen-t9a.example.; 2083; RADIUS/TLS; 20; 60)

    } // minimum TTL is 47, up'ed to MIN_EFF_TTL

12. Continuing at 18.
13. (not executed)
14. (not executed)
15. (not executed)
16. (not executed)
17. (not executed)
18. O-1 = {
    • (2001:0DB8::202:44ff:fe0a:f704; 2083; RADIUS/TLS; 10; 60),
    • (192.0.2.7; 2083; RADIUS/TLS; 20; 60)

    }; O-2 = 0

19. No match with own listening address; terminate with tuple (O-1, O-2) from previous step.

The implementation will then attempt to connect to two servers, with preference to [2001:0DB8::202:44ff:fe0a:f704]:2083 using the RADIUS/TLS protocol.

4. Operations and Manageability Considerations

The discovery algorithm as defined in this document contains several options; the major ones being use of NAPTR vs. SRV; how to determine the authorization status of a contacted server for a given realm; which trust anchors to consider trustworthy for the RADIUS conversation setup.

Random parties which do not agree on the same set of options may not be able to interoperate. However, such a global interoperability is not intended by this document.

Discovery as per this document becomes important inside a roaming consortium, which has set up roaming agreements with the other partners. Such roaming agreements require much more than a technical means of server discovery; there are administrative and contractual considerations at play (service contracts, backoffice compensations, procedures, ...).

A roaming consortium's roaming agreement must include a profile of which choice points of this document to use. So long as the roaming consortium can settle on one deployment profile, they will be able to interoperate based on that choice; this per-consortium interoperability is the intended scope of this document.

5. Security Considerations

When using DNS without DNSSEC security extensions and validation for all of the replies to NAPTR, SRV and A/AAAA requests as described in section Section 3, the result O can not be trusted. Even if it can be trusted (i.e. DNSSEC is in use), actual authorization of the discovered server to provide service for the given realm needs to be verified. A mechanism from section Section 2.1.1.3 or equivalent MUST be used to verify authorization.

The algorithm has a configurable completion time-out DNS_TIMEOUT defaulting to three seconds for RADIUS' operational reasons. The lookup of DNS resource records based on unverified user input is an attack vector for DoS attacks: an attacker might intentionally craft bogus DNS zones which take a very long time to reply (e.g. due to a particularly byzantine tree structure, or artificial delays in responses).

To mitigate this DoS vector, implementations SHOULD consider rate-limiting either their amount of new executions of the dynamic discovery algorithm as a whole, or the amount of intermediate responses to track, or at least the number of pending DNS queries. Implementations MAY choose lower values than the default for DNS_TIMEOUT to limit the impact of DoS attacks via that vector. They MAY also continue their attempt to resolve DNS records even after DNS_TIMEOUT has passed; a subsequent request for the same realm might benefit from retrieving the results anyway. The amount of time to spent waiting for a result will influence the impact of a possible DoS attack; the waiting time value is implementation dependent and outside the scope of this specification.

With Dynamic Discovery being enabled for a RADIUS Server, and depending on the deployment scenario, the server may need to open up its target IP address and port for the entire internet, because arbitrary clients may discover it as a target for their authentication requests. If such clients are not part of the roaming consortium, the RADIUS/TLS connection setup phase will fail (which is intended) but the computational cost for the connection attempt is significant. With the port for a TLS-based service open, the RADIUS server shares all the typical attack vectors for services based on TLS (such as HTTPS, SMTPS, ...). Deployments of RADIUS/TLS with Dynamic Discovery should consider these attack vectors and take appropriate counter-measures (e.g. blacklisting known-bad IPs on a firewall, rate-limiting new connection attempts, etc.).

6. Privacy Considerations

The classic RADIUS operational model (known, pre-configured peers, shared secret security, mostly plaintext communication) and this new RADIUS dynamic discovery model (peer discovery with DNS, PKI security and packet confidentiality) differ significantly in their impact on the privacy of end users trying to authenticate to a RADIUS server.

With classic RADIUS, traffic in large environments gets aggregated by statically configured clearinghouses. The packets sent to those clearinghouses and their responses are mostly unprotected. As a consequence,

• All intermediate IP hops can inspect most of the packet payload in clear text, including the User-Name and Calling-Station-Id attributes, and can observe which client sent the packet to which clearinghouse. This allows the creation of mobility profiles for any passive observer on the IP path.
• The existence of a central clearinghouse creates an opportunity for the clearinghouse to trivially create the same mobility profiles. The clearinghouse may or may not be trusted not to do this, e.g. by sufficiently threatening contractual obligations.
• In addition to that, with the clearinghouse being a RADIUS intermediate in possession of a valid shared secret, the clearinghouse can observe and record even the security-critical RADIUS attributes such as User-Password. This risk may be mitigated by choosing authentication payloads which are cryptographically secured and do not use the attribute User-Password - such as certain EAP types.
• There is no additional information disclosure to parties outside the IP path between the RADIUS client and server (in particular, no DNS servers learn about realms of current ongoing authentications).

With RADIUS and dynamic discovery,

• This protocol allows for RADIUS clients to identify and directly connect to the RADIUS home server. This can eliminate the use of clearinghouses to do forwarding of requests, and it also eliminates the ability of the clearinghouse to then aggregate the user information that flows through it. However, there exist reasons why clearinghouses might still be used. One reason to keep a clearinghouse is to act as a gateway for multiple backends in a company; another reason may be a requirement to sanitise RADIUS datagrams (filter attributes, tag requests with new attributes, ... ).
• Even where intermediate proxies continue to be used for reasons unrelated to dynamic discovery, the number of such intermediates may be reduced by removing those proxies which are only deployed for pure request routing reasons. This reduces the number of entities which can inspect the RADIUS traffic.
• RADIUS clients which make use of dynamic discovery will need to query the Domain Name System, and use a user's realm name as the query label. A passive observer on the IP path between the RADIUS client and the DNS server(s) being queried can learn that a user of that specific realm was trying to authenticate at that RADIUS client at a certain point in time. This may or may not be sufficient for the passive observer to create a mobility profile. During the recursive DNS resolution, a fair number of DNS servers and the IP hops in between those get to learn that information. Not every single authentication triggers DNS lookups, so there is no one-to-one relation of leaked realm information and the number of authentications for that realm.
• Since dynamic discovery operates on a RADIUS hop-by-hop basis, there is no guarantee that the RADIUS payload is not transmitted between RADIUS systems which do not make use of this algorithm, and possibly using other transports such as RADIUS/UDP. On such hops, the enhanced privacy is jeopardized.

In summary, with classic RADIUS, few intermediate entities learn very detailed data about every ongoing authentications, while with dynamic discovery, many entities learn only very little about recently authenticated realms.

7. IANA Considerations

This document requests IANA registration of the following entries in existing registries:

• S-NAPTR Application Service Tags registry
  • aaa+auth
  • aaa+acct
  • aaa+dynauth

• S-NAPTR Application Protocol Tags registry
  • radius.tls
  • radius.dtls

This document reserves the use of the "radiustls" and "radiusdtls" service names. Registration information as per [RFC6335] section 8.1.1 is as follows:

• Service Name: radiustls; radiusdtls
• Transport Protocols: TCP, UDP
• Assignee: IESG <iesg@ietf.org>
• Contact: IETF Chair <chair@ietf.org>
• Description: Authentication, Accounting and Dynamic authorization via the RADIUS protocol. These service names are used to construct the SRV service labels "_radiustls" and "_radiusdtls" for discovery of RADIUS/TLS and RADIUS/DTLS servers, respectively.
• Reference: RFC Editor Note: please insert the RFC number of this document. The protocol does not use broadcast, multicast or anycast communication.

This document requests the creation of a new IANA registry named "RADIUS/TLS SRV Protocol Registry" with the following initial entries:

• _tcp
• _udp

This document requires that a number of Object Identifiers be assigned. They re now under the control of IANA following [I-D.housley-pkix-oids].

IANA is requested to assign the following identifiers:

• TBD99 is to be assigned from the "SMI Security for PKIX Module Identifier Registry". The suggested description is id-mod-nai-realm-08.
• TBD98 is to be assigned from the "SMI Security for PKIX Other Name Forms Registry." The suggested description is id-on-nai.

RFC Editor Note: please replace the occurences of TBD98 and TBD99 in Appendix A of the document with the actually assigned numbers.

8. References

8.1. Normative References

[RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782]	Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000.
[RFC2865]	Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000.
[RFC2866]	Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC3958]	Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC4282]	Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network Access Identifier", RFC 4282, December 2005.
[RFC5176]	Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 5176, January 2008.
[RFC5280]	Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R. and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008.
[RFC5580]	Tschofenig, H., Adrangi, F., Jones, M., Lior, A. and B. Aboba, "Carrying Location Objects in RADIUS and Diameter", RFC 5580, August 2009.
[RFC5891]	Klensin, J., "Internationalized Domain Names in Applications (IDNA): Protocol", RFC 5891, August 2010.
[I-D.ietf-radext-dtls]	DeKok, A., "DTLS as a Transport Layer for RADIUS", Internet-Draft draft-ietf-radext-dtls-04, April 2013.
[RFC6614]	Winter, S., McCauley, M., Venaas, S. and K. Wierenga, "Transport Layer Security (TLS) Encryption for RADIUS", RFC 6614, May 2012.
[I-D.ietf-radext-nai]	DeKok, A., "The Network Access Identifier", Internet-Draft draft-ietf-radext-nai-03, May 2013.

8.2. Informative References

[RFC4017]	Stanley, D., Walker, J. and B. Aboba, "Extensible Authentication Protocol (EAP) Method Requirements for Wireless LANs", RFC 4017, March 2005.
[RFC6335]	Cotton, M., Eggert, L., Touch, J., Westerlund, M. and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, August 2011.
[RFC6733]	Fajardo, V., Arkko, J., Loughney, J. and G. Zorn, "Diameter Base Protocol", RFC 6733, October 2012.

Appendix A. Appendix A: ASN.1 Syntax of NAIRealm

PKIXNaiRealm08 {iso(1) identified-organization(3) dod(6)
     internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
     id-mod-nai-realm-08 (TBD99) }

 DEFINITIONS EXPLICIT TAGS ::=

 BEGIN

 -- EXPORTS ALL --

 IMPORTS

    id-pkix
    FROM PKIX1Explicit-2009
        {iso(1) identified-organization(3) dod(6) internet(1)
         security(5) mechanisms(5) pkix(7) id-mod(0)
         id-mod-pkix1-explicit-02(51)}
           -- from RFC 5280, RFC 5912

    OTHER-NAME
    FROM PKIX1Implicit-2009
       {iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)}
             -- from RFC 5280, RFC 5912
 ;


 -- Service Name Object Identifier

 id-on   OBJECT IDENTIFIER ::= { id-pkix 8 }

 id-on-nai OBJECT IDENTIFIER ::= { id-on TBD98 }

 -- Service Name

 naiRealm OTHER-NAME ::= { NAIRealm IDENTIFIED BY { id-on-nai }}

 NAIRealm ::= UTF8String (SIZE (1..MAX))

 END

Authors' Addresses