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INTERNET-DRAFT Jonathan Trostle
draft-ietf-cat-iakerb-09.txt Cisco Systems
Updates: RFC 1510, 1964 Michael Swift
October 2002 University of WA
Bernard Aboba
Microsoft
Glen Zorn
Cisco Systems
Initial and Pass Through Authentication Using Kerberos V5 and the GSS-API
(IAKERB)
<draft-ietf-cat-iakerb-09.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [5].
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.
This draft expires in March 2003. Please send comments to the
authors.
1. Abstract
This document defines extensions to the Kerberos protocol
specification (RFC 1510 [1]) and GSSAPI Kerberos protocol mechanism
(RFC 1964 [2]) that enables a client to obtain Kerberos tickets for
services where the KDC is not accessible to the client, but is
accessible to the application server. Some common scenarios where
lack of accessibility would occur are when the client does not have
an IP address prior to authenticating to an access point, the client
is unable to locate a KDC, or a KDC is behind a firewall. The
document specifies two protocols to allow a client to exchange KDC
messages (which are GSS encapsulated) with an IAKERB proxy instead of
a KDC.
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2. Conventions used in this document
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 RFC2119 [6].
3. Motivation
When authenticating using Kerberos V5, clients obtain tickets from a
KDC and present them to services. This method of operation works well
in many situations, but is not always applicable. The following is a
list of some of the scenarios that this proposal addresses:
(1) The client must initially authenticate to an access point in
order to gain full access to the network. Here the client may be
unable to directly contact the KDC either because it does not have an
IP address, or the access point packet filter does not allow the
client to send packets to the Internet before it authenticates to the
access point [8].
(2) A KDC is behind a firewall so the client will send Kerberos
messages to the IAKERB proxy which will transmit the KDC request and
reply messages between the client and the KDC. (The IAKERB proxy is a
special type of Kerberos application server that also relays KDC
request and reply messages between a client and the KDC).
4. Overview
This proposal specifies two protocols that address the above
scenarios: the IAKERB proxy option and the IAKERB minimal messages
option. In the IAKERB proxy option (see Figure 1) an application
server called the IAKERB proxy acts as a protocol gateway and proxies
Kerberos messages back and forth between the client and the KDC. The
IAKERB proxy is also responsible for locating the KDC and may
additionally perform other application proxy level functions such as
auditing. A compliant IAKERB proxy MUST implement the IAKERB proxy
protocol.
Client <---------> IAKERB proxy <----------> KDC
Figure 1: IAKERB proxying
The second protocol is the minimal messages protocol which is based
on user-user authentication [4]; this protocol is targetted at
environments where the number of messages, prior to key
establishment, needs to be minimized. In the normal minimal messages
protocol, the client sends its ticket granting ticket (TGT) to the
IAKERB proxy (in a KRB_TKT_PUSH message) for the TGS case. The IAKERB
proxy then sends a TGS_REQ to the KDC with the client's TGT in the
additional tickets field of the TGS_REQ message. The returned ticket
will list the client as the ticket's server principal, and will be
encrypted with the session key from the client's TGT. The IAKERB
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proxy then uses this ticket to generate an AP request that is sent to
the client (see Figure 2). Thus mutual authentication is accomplished
with three messages between the client and the IAKERB proxy versus
four or more (the difference is larger if crossrealm operations are
involved).
Subsequent to mutual authentication and key establishment, the IAKERB
proxy sends a ticket to the client (in a KRB_TKT_PUSH message). This
ticket is created by the IAKERB proxy and contains the same fields as
the original service ticket that the proxy sent in the AP_REQ
message, except the client and server names are reversed and it is
encrypted in a long term key known to the IAKERB proxy. Its purpose
is to enable fast subsequent re-authentication by the client to the
application server (using the conventional AP request AP reply
exchange) for subsequent sessions. In addition to minimizing the
number of messages, a secondary goal is to minimize the number of
bytes transferred between the client and the IAKERB proxy prior to
mutual authentication and key establishment. Therefore, the final
service ticket (the reverse ticket) is sent after mutual
authentication and key establishment is complete, rather than as part
of the initial AP_REQ from the IAKERB proxy to the client. Thus
protected application data (e.g., GSS signed and wrapped messages)
can flow before this final message is sent.
The AS_REQ case for the minimal messages option is similar, where the
client sends up the AS_REQ message and the IAKERB proxy forwards it
to the KDC. The IAKERB proxy pulls the client TGT out of the AS_REP
message; the protocol now proceeds as in the TGS_REQ case described
above with the IAKERB proxy including the client's TGT in the
additional tickets field of the TGS_REQ message.
A compliant IAKERB proxy MUST implement the IAKERB proxy protocol,
and MAY implement the IAKERB minimal message protocol. In general,
the existing Kerberos paradigm where clients contact the KDC to
obtain service tickets should be preserved where possible.
For most IAKERB scenarios, such as when the client does not have an
IP address, or cannot directly contact a KDC, the IAKERB proxy
protocol should be adequate. If the client needs to obtain a
crossrealm TGT (and the conventional Kerberos protocol cannot be
used), then the IAKERB proxy protocol must be used. In a scenario
where the client does not have a service ticket for the target
server, it is crucial that the number of messages between the client
and the target server be minimized (especially if the client and
target server are in different realms), and/or it is crucial that the
number of bytes transferred between the client and the target server
be minimized, then the client should consider using the minimal
messages protocol. The reader should see the security considerations
section regarding the minimal messages protocol.
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Client --------> IAKERB proxy
TKT_PUSH (w/ TGT)
Client IAKERB proxy --------------------> KDC
TGS_REQ with client
TGT as additional TGT
Client IAKERB proxy <-------------------- KDC
TGS_REP with service
ticket
Client <-------- IAKERB proxy KDC
AP_REQ
Client --------> IAKERB proxy KDC
AP_REP
-------------------------------------------------------------
post-key establishment and application data flow phase:
Client <-------- IAKERB proxy KDC
TKT_PUSH (w/ticket targetted at IAKERB proxy
to enable fast subsequent authentication)
Figure 2: IAKERB Minimal Messages Option: TGS case
5. GSSAPI Encapsulation
The mechanism ID for IAKERB proxy GSS-API Kerberos, in accordance
with the mechanism proposed by SPNEGO [7] for negotiating protocol
variations, is: {iso(1) org(3) dod(6) internet(1) security(5)
mechanisms(5) iakerb(10) iakerbProxyProtocol(1)}. The proposed
mechanism ID for IAKERB minimum messages GSS-API Kerberos, in
accordance with the mechanism proposed by SPNEGO for negotiating
protocol variations, is: {iso(1) org(3) dod(6) internet(1)
security(5) mechanisms(5) iakerb(10)
iakerbMinimumMessagesProtocol(2)}.
NOTE: An IAKERB implementation does not require SPNEGO in order to
achieve interoperability with other IAKERB peers. Two IAKERB
implementations may interoperate in the same way that any two peers
can interoperate using a pre-established GSSAPI mechanism. The above
OID's allow two SPNEGO peers to securely negotiate IAKERB from among
a set of GSS mechanisms.
The AS request, AS reply, TGS request, and TGS reply messages are all
encapsulated using the format defined by RFC1964 [2]. This consists
of the GSS-API token framing defined in appendix B of [3]:
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InitialContextToken ::= [APPLICATION 0] IMPLICIT SEQUENCE {
thisMech MechType
-- MechType is OBJECT IDENTIFIER
-- representing iakerb proxy or iakerb min messages
innerContextToken ANY DEFINED BY thisMech
-- contents mechanism-specific;
-- ASN.1 usage within innerContextToken
-- is not required
}
The innerContextToken consists of a 2-byte TOK_ID field (defined
below), followed by the Kerberos V5 KRB_AS_REQ, KRB_AS_REP,
KRB_TGS_REQ, or KRB_TGS_REP messages, as appropriate. The TOK_ID
field shall be one of the following values, to denote that the
message is either a request to the KDC or a response from the KDC.
Message TOK_ID
KRB_KDC_REQ 00 03
KRB_KDC_REP 01 03
We also define the token ID for the KRB_TKT_PUSH token (defined below
and used in the minimal messages variation):
Message TOK_ID
KRB_TKT_PUSH 02 03
For completeness, we list the other RFC 1964 defined token ID's here:
Message TOK_ID
AP_REQ 01 00
AP_REP 02 00
KRB_ERROR 03 00
6. The IAKERB proxy protocol
The IAKERB proxy will proxy Kerberos KDC request, KDC reply, and
KRB_ERROR messages back and forth between the client and the KDC as
illustrated in Figure 1. Messages received from the client must first
have the Kerberos GSS header (RFC1964 [2]) stripped off. The
unencapsulated message will then be forwarded to a KDC. The IAKERB
proxy is responsible for locating an appropriate KDC using the realm
information in the KDC request message it received from the client.
In addition, the IAKERB proxy SHOULD implement a retry algorithm for
KDC requests over UDP (including selection of alternate KDC's if the
initial KDC does not respond to its requests). For messages sent by
the KDC, the IAKERB proxy encapsulates them with a Kerberos GSS
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header before sending them to the client.
We define two new Kerberos error codes that allow the proxy to
indicate the following error conditions to the client:
(a) when the proxy is unable to obtain an IP address for a KDC in the
client's realm, it sends the KRB_IAKERB_ERR_KDC_NOT_FOUND KRB_ERROR
(80) message to the client.
(b) when the proxy has an IP address for a KDC in the client realm,
but does not receive a response from any KDC in the realm (including
in response to retries), it sends the KRB_IAKERB_ERR_KDC_NO_RESPONSE
KRB_ERROR (81) message to the client.
To summarize, the sequence of steps for processing is as follows:
Servers:
1. For received KDC_REQ messages (with token ID 00 03)
- process GSS framing (check OID)
if the OID is not one of the two OID's specified in the GSSAPI
Encapsulation section above, then process according to mechanism
defined by that OID (if the OID is recognized). The processing
is outside the scope of this specification. Otherwise, strip
off GSS framing.
- find KDC for specified realm (if KDC IP address cannot be
obtained, send a KRB_ERROR message with error code
KRB_IAKERB_ERR_KDC_NOT_FOUND to the client).
- send to KDC (storing client IP address, port, and indication
whether IAKERB proxy option or minimal messages option is
being used)
- retry with same or another KDC if no response is received. If
the retries also fail, send an error message with error code
KRB_IAKERB_ERR_KDC_NO_RESPONSE to the client.
2. For received KDC_REP messages
- encapsulate with GSS framing, using token ID 01 03 and the OID
that corresponds to the stored protocol option
- send to client (using the stored client IP address and port)
3. For KRB_ERROR messages received from the KDC
- encapsulate with GSS framing, using token ID 03 00 and the OID
that corresponds to the stored protocol option
- send to client (using the stored client IP address and port)
(one possible exception is the KRB_ERR_RESPONSE_TOO_BIG error
which can lead to a retry of the KDC_REQ message over the TCP
transport by the server, instead of simply proxying the error
to the client).
4. For sending/receiving AP_REQ and AP_REP messages
- process per RFC 1510 and RFC 1964; the created AP_REP message
SHOULD include the subkey (with same etype as the session key)
to facilitate use with other key derivation algorithms outside
of [2]. The subkey SHOULD be created using locally generated
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entropy as one of the inputs (in addition to other inputs
such as the session key).
Clients:
1. For sending KDC_REQ messages
- create AS_REQ or TGS_REQ message
- encapsulate with GSS framing (token ID 00 03 and OID
corresponding to the protocol option).
- send to server
2. For received KDC_REP messages
- decapsulate by removing GSS framing (token ID 01 03)
- process inner Kerberos message according to RFC 1510
3. For received KRB_ERROR messages
- decapsulate by removing GSS framing (token ID 03 00)
- process inner Kerberos message according to RFC 1510
and possibly retry the request (time skew errors lead
to retries in most existing Kerberos implementations)
4. For sending/receiving AP_REQ and AP_REP messages
- process per RFC 1510 and RFC 1964; the created AP_REQ
message SHOULD include the subsession key in the
authenticator field.
7. The IAKERB minimal messages protocol
The client MAY initiate the IAKERB minimal messages variation when
the number of messages must be minimized (the most significant
reduction in the number of messages can occur when the client and the
IAKERB proxy are in different realms). SPNEGO [7] MAY be used to
securely negotiate between the protocols (and amongst other GSS
mechanism protocols). A compliant IAKERB server MAY support the
IAKERB minimal messages protocol.
(a) AS_REQ case: (used when the client does not have a TGT)
We apply the Kerberos user-user authentication protocol [4] in this
scenario (other work in this area includes the IETF work in progress
effort to apply Kerberos user user authentication to DHCP
authentication).
The client indicates that the minimal message sub-protocol will be
used by using the appropriate OID as described above. The client
sends the GSS encapsulated AS_REQ message to the IAKERB proxy, and
the IAKERB proxy processes the GSS framing (as described above for
the IAKERB proxy option) and forwards the AS_REQ message to the KDC.
The IAKERB proxy will either send a KRB_ERROR message back to the
client, or it will send an initial context token consisting of the
GSS header (minimal messages OID with a two byte token header 01 03),
followed by an AS_REP message. The AS_REP message will contain the
AP_REQ message in a padata field; the ticket in the AP_REQ is a
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user-user ticket encrypted in the session key from the client's
original TGT. We define the padata type PA-AP-REQ with type number
25. The corresponding padata value is the AP_REQ message without any
GSS framing. For the IAKERB minimal messages AS option, the AP_REQ
message authenticator MUST include the RFC 1964 [2] checksum. The
mutual-required and use-session-key flags are set in the ap-options
field of the AP_REQ message.
The protocol is complete in the KRB_ERROR case (from the server
perspective, but the client should retry depending on the error
type). If the IAKERB proxy receives an AS_REP message from the KDC,
the IAKERB proxy will then obtain the client's TGT from the AS_REP
message. The IAKERB proxy then sends a TGS_REQ message with the
client's TGT in the additional tickets field to the client's KDC
(ENC-TKT-IN-SKEY option).
The IAKERB proxy MAY handle returned KRB_ERROR messages and retry the
TGS request message (e.g. on a KRB_ERR_RESPONSE_TOO_BIG error,
switching to TCP from UDP). Ultimately, the IAKERB proxy either
proxies a KRB_ERROR message to the client (after adding the GSS
framing), sends one of the new GSS framed KRB_ERROR messages defined
above, or it receives the TGS_REP message from the KDC and then
creates the AP_REQ message according to RFC 1964 [2]. The IAKERB
proxy then sends a GSS token containing the AS_REP message with the
AP_REQ message in the padata field as described above. (Note:
although the server sends the context token with the AP_REQ, the
client is the initiator.) The IAKERB proxy MUST set both the mutual-
required and use-session-key flags in the AP_REQ message in order to
cause the client to authenticate as well. The authenticator SHOULD
include the subsession key (containing locally added entropy). The
client will reply with the GSSAPI enscapsulated AP_REP message, if
the IAKERB proxy's authentication succeeds (which SHOULD include the
subkey field to facilitate use with other key derivation algorithms
outside of [2]). If all goes well, then, in order to enable
subsequent efficient client authentications, the IAKERB proxy will
then send a final message of type KRB_TKT_PUSH containing a Kerberos
ticket (the reverse ticket) that has the IAKERB client principal
identifier in the client identifier field of the ticket and its own
principal identity in the server identifier field of the ticket (see
Figure 3):
KRB_TKT_PUSH :: = [APPLICATION 17] SEQUENCE {
pvno[0] INTEGER, -- 5 (protocol version)
msg-type[1] INTEGER, -- 17 (message type)
ticket[2] Ticket
}
NOTE: The KRB_TKT_PUSH message must be encoded using ASN.1 DER. The
key used to encrypt the reverse ticket is a long term secret key
chosen by the IAKERB proxy. The fields are identical to the AP_REQ
ticket, except the client name will be switched with the server name,
and the server realm will be switched with the client realm. (The one
other exception is that addresses should not be copied from the
AP_REQ ticket to the reverse ticket). Sending the reverse ticket
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allows the client to efficiently initiate subsequent reauthentication
attempts with a RFC1964 AP_REQ message. Note that the TKT_PUSH
message is sent after mutual authentication and key establishment are
complete.
Client --------> IAKERB proxy --------------------> KDC
AS_REQ AS_REQ
Client IAKERB proxy <-------------------- KDC
AS_REP w/ client TGT
Client IAKERB proxy --------------------> KDC
TGS_REQ with client
TGT as additional TGT
Client IAKERB proxy <-------------------- KDC
TGS_REP with service
ticket
Client <-------- IAKERB proxy KDC
AS_REP w/ AP_REQ in padata field
Client --------> IAKERB proxy KDC
AP_REP
-------------------------------------------------------------
post-key establishment and application data flow phase:
Client <-------- IAKERB proxy KDC
TKT_PUSH (w/ticket targetted at IAKERB proxy
to enable fast subsequent authentication)
Figure 3: IAKERB Minimal Messages Option: AS case
(b) TGS_REQ case: (used when the client has a TGT)
The client indicates that the minimal messages sub-protocol will be
used by using the appropriate OID as described above. The client
initially sends a KRB_TKT_PUSH message (with the GSS header) to the
IAKERB proxy in order to send it a TGT. The IAKERB proxy will obtain
the client's TGT from the KRB_TKT_PUSH message and then proceed to
send a TGS_REQ message to a KDC where the realm of the KDC is equal
to the realm from the server realm field in the TGT sent by the
client in the KRB_TKT_PUSH message. NOTE: this realm could be the
client's home realm, the proxy's realm, or an intermediate realm. The
protocol then continues as in the minimal messages AS_REQ case
described above (see Figure 2); the IAKERB proxy's TGS_REQ message
contains the client's TGT in the additional tickets field (ENC-TKT-
IN-SKEY option). The IAKERB proxy then receives the TGS_REP message
from the KDC and then sends a RFC 1964 AP_REQ message to the client
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(with the MUTUAL AUTH flag set - see AS_REQ case).
To summarize, here are the steps for the minimal messages TGS
protocol:
Client:
(has TGT already for, or targetted at, realm X.ORG)
sends TKT_PUSH message to server containing client's ticket
for X.ORG (which could be a crossrealm TGT)
Server:
(has TGT already targetted at realm X.ORG)
sends to KDC (where KDC has principal id = server name,
server realm from client ticket) a TGS_REQ:
TGT in TGS_REQ is server's TGT
Additional ticket in TGS_REQ is client's TGT from TKT_PUSH
message
Server name in TGS_REQ (optional by rfc1510) is not present
Server realm in TGS_REQ is realm in server's TGT - X.ORG
KDC:
Builds a ticket:
Server name = client's name
Client name = server's name, Client realm = server's realm
Server realm = client's realm
Encrypted with: session key from client's TGT (passed in
additional tickets field)
Build a TGS_REP
Encrypted with session key from server's TGT
Sends TGS_REP and ticket to server
Server:
Decrypts TGS_REP from KDC using session key from its TGT
Constructs AP_REQ
Ticket = ticket from KDC (which was encrypted with
client's TGT session key)
authenticator clientname = server's name (matches
clientname in AP-REQ ticket)
authenticator clientrealm = server's realm
subsession key in authenticator is present (same
etype as the etype of the session key in the ticket)
checksum in authenticator is the RFC 1964 checksum
sequence number in authenticator is present (RFC 1964)
ap-options has both use-session-key and mutual-required
flags set
Sends AP_REQ (with GSS-API framing) to client
Client:
Receives AP_REQ
Decrypts ticket using session key from its TGT
Verifies AP_REQ
Builds AP_REP and sends to server (AP_REP SHOULD include
subkey field to facilitate use with other key derivation
algorithms outside of [2] e.g., [8] and its successors.
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Some apps may have their own message protection key
derivation algorithm and protected message format.
AP_REP includes the sequence number per RFC 1964.)
Server:
Verifies AP-REP. Builds reverse ticket as described above
and sends reverse ticket to client using the KRB_TKT_PUSH
message. The reverse ticket is the same as the AP_REQ
ticket except the client name, realm are switched with the
server name, realm fields and it is encrypted in a secret
key known to the IAKERB proxy.
8. Addresses in Tickets
In IAKERB, the machine sending requests to the KDC is the server and
not the client. As a result, the client should not include its
addresses in any KDC requests for two reasons. First, the KDC may
reject the forwarded request as being from the wrong client. Second,
in the case of initial authentication for a dial-up client, the
client machine may not yet possess a network address. Hence, as
allowed by RFC1510 [1], the addresses field of the AS and TGS
requests SHOULD be blank and the caddr field of the ticket SHOULD
similarly be left blank.
9. Security Considerations
Similar to other network access protocols, IAKERB allows an
unauthenticated client (possibly outside the security perimeter of an
organization) to send messages that are proxied to interior servers.
When combined with DNS SRV RR's for KDC lookup, there is the
possibility that an attacker can send an arbitrary message to an
interior server. There are several aspects to note here:
(1) in many scenarios, compromise of the DNS lookup will require the
attacker to already have access to the internal network. Thus the
attacker would already be able to send arbitrary messages to interior
servers. No new vulnerabilities are added in these scenarios.
(2) in a scenario where DNS SRV RR's are being used to locate the
KDC, IAKERB is being used, and an external attacker can modify DNS
responses to the IAKERB proxy, there are several countermeasures to
prevent arbitrary messages from being sent to internal servers:
(a) KDC port numbers can be statically configured on the IAKERB
proxy. In this case, the messages will always be sent to KDC's. For
an organization that runs KDC's on a static port (usually port 88)
and does not run any other servers on the same port, this
countermeasure would be easy to administer and should be effective.
(b) the proxy can do application level sanity checking and filtering.
This countermeasure should eliminate many of the above attacks.
(c) DNS security can be deployed. This countermeasure is probably
overkill for this particular problem, but if an organization has
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already deployed DNS security for other reasons, then it might make
sense to leverage it here. Note that Kerberos could be used to
protect the DNS exchanges. The initial DNS SRV KDC lookup by the
proxy will be unprotected, but an attack here is at most a denial of
service (the initial lookup will be for the proxy's KDC to facilitate
Kerberos protection of subsequent DNS exchanges between itself and
the DNS server).
In the minimal messages protocol option, the application server sends
an AP_REQ message to the client. The ticket in the AP_REQ message
SHOULD NOT contain authorization data since some operating systems
may allow the client to impersonate the server and increase its own
privileges. If the ticket from the server connotes any authorization,
then the minimal messages protocol should not be used. Also, the
minimal messages protocol may facilitate denial of service attacks in
some environments; to prevent these attacks, it may make sense for
the minimal messages protocol server to only accept a KRB_TGT_PUSH
message on a local network interface (to ensure that the message was
not sent from a remote malicious host).
10. Acknowledgements
We thank the Kerberos Working Group chair, Doug Engert, for his
efforts in helping to progress this specification. We also thank Ken
Raeburn for his comments and the other working group participants for
their input.
11. References
[1] J. Kohl, C. Neuman, "The Kerberos Network Authentication
Service (V5)", RFC 1510.
[2] J. Linn, "The Kerberos Version 5 GSS-API Mechanism", RFC 1964.
[3] J. Linn, "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743.
[4] D. Davis, R. Swick, "Workstation Services and Kerberos
Authentication at Project Athena", Technical Memorandum TM-424,
MIT Laboratory for Computer Science, February 1990.
[5] S. Bradner, "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[6] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[7] E. Baize, D. Pinkas, "The Simple and Protected GSS-API Negotiation
Mechanism," RFC 2478, December 1998.
[8] Part 11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specifications, ANSI/IEEE Std. 802.11, 1999 Edition.
Trostle, Swift, Aboba, Zorn [Page 12]
INTERNET DRAFT October 2002 Expires March 2003
12. Author's Addresses
Jonathan Trostle
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134, U.S.A.
Email: jtrostle@cisco.com
Phone: (408) 527-6201
Michael Swift
University of Washington
Seattle, WA
Email: mikesw@cs.washington.edu
Bernard Aboba
Microsoft
One Microsoft Way
Redmond, Washington, 98052, U.S.A.
Email: bernarda@microsoft.com
Phone: (425) 706-6605
Glen Zorn
Cisco Systems
Bellevue, WA U.S.A.
Email: gwz@cisco.com
Phone: (425) 468-0955
This draft expires on March 31st, 2003.
Trostle, Swift, Aboba, Zorn [Page 13]
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