Network Working Group V. Devarapalli
Internet-Draft WiChorus
Intended status: Standards Track K. Weniger
Expires: September 10, 2009 March 9, 2009
Redirect Mechanism for IKEv2
draft-ietf-ipsecme-ikev2-redirect-05.txt
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Abstract
IKEv2 is a protocol for setting up VPN tunnels from a remote location
to a gateway so that the VPN client can access services in the
network behind the gateway. Currently there is no standard mechanism
specified that allows an overloaded VPN gateway or a VPN gateway that
is being shut down for maintenance to redirect the VPN client to
attach to another gateway. This document proposes a redirect
mechanism for IKEv2. The proposed mechanism can also be used in
Mobile IPv6 to enable the home agent to redirect the mobile node to
another home agent.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IKEv2 Exchange with Redirect . . . . . . . . . . . . . . . . . 4
4. Use of Anycast Addresses with the Redirect Mechanism . . . . . 5
5. Gateway Initiated Redirect . . . . . . . . . . . . . . . . . . 6
6. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 7
6.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 7
6.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 9
7. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
IKEv2 [2] is used for setting up IPsec-based VPNs. The IP address of
the VPN gateway can be configured on the VPN client. But this does
not scale well, when the number of VPN gateways is large. Dynamic
discovery of VPN gateways using DNS is quite widely used too.
However, using DNS is not flexible when it comes to assigning a VPN
gateway to the VPN client based on the load on the VPN gateways. The
VPN client typically tries to connect to the IP address of the VPN
gateways that appears first in the DNS response. If the VPN tunnel
setup fails, then the VPN client tries to attach to the other VPN
gateways returned in the DNS response.
This document proposes a redirect mechanism for IKEv2 that enables a
VPN gateway to redirect the VPN client to another VPN gateway, for
example, based on the load condition. The redirect can be done
during during the IKE_SA_INIT or the IKE_AUTH exchange. Gateway-
initiated redirect in the middle of a session is also supported. The
redirect mechanism can also be used in conjunction with anycast
addresses. In this case, anycast address for the cluster of VPN
gateways is stored in the DNS instead of a list of unicast IP
addresses of the VPN gateways.
The redirect can also happen because of administrative or optimal
routing reasons. This document does not attempt to provide an
exhaustive list of reasons for redirecting a VPN client to another
VPN gateway.
Mobile IPv6 [3] may use IKEv2 for mutual authentication between the
mobile node and the home agent. IKEv2 may also be used for home
address configuration and setting up IPsec security associations for
protecting Mobile IPv6 signaling messages [4]. The IKEv2 exchange
precedes the exchange of Mobile IPv6 signaling messages. Therefore
the mechanism described in this document can be also be used by a
Mobile IPv6 home agent to redirect a mobile node to another home
agent.
There is a Home Agent Switch mechanism available for redirecting a
mobile node to another home agent, described in [5]. The Home Agent
Switch mechanism can only be used after the binding cache had been
created at the home agent for the mobile node. The disadvantage with
this is that quite a bit of state is created on the home agent before
the mobile node can be redirected to another home agent. The
mechanism described in this document can be used for redirecting a
mobile node before any state related to the Mobile IPv6 binding is
created on the home agent.
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2. Terminology
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 [1].
3. IKEv2 Exchange with Redirect
To redirect an IKEv2 session to another VPN gateway, the VPN gateway
that initially received the IKE_SA_INIT request selects another VPN
gateway and responds to the VPN client with a REDIRECT Notification
payload. The mechanism by which the initial VPN gateway selects
another VPN gateway is out of scope for this document. The IP
address of the selected VPN gateway is sent in the REDIRECT payload.
The VPN client indicates support for the IKEv2 redirect mechanism by
including a REDIRECT_SUPPORTED notification message in the initial
IKE_SA_INIT request. If the IKE_SA_INIT request did not include the
REDIRECT_SUPPORTED payload, the responder MUST NOT send the REDIRECT
payload to the VPN client.
Initiator Responder (initial VPN GW)
--------- -------------------------
(IP_I:500 -> Initial_IP_R:500)
HDR(A,0), SAi1, KEi, Ni, -->
N(REDIRECT_SUPPORTED)
(Initial_IP_R:500 -> IP_I:500)
<-- HDR(A,0), N(REDIRECT, IP_R)
When the VPN client receives the IKE_SA_INIT response with the
REDIRECT payload, it initiates a new IKE_SA_INIT exchange with the
VPN gateway listed in the REDIRECT payload. The VPN client includes
the IP address of the original VPN gateway that redirected the
client. The IKEv2 exchange then proceeds as normal with the selected
VPN gateway.
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Initiator Responder (Selected VPN GW)
--------- ---------------------------
(IP_I:500 -> IP_R:500)
HDR(A,0), SAi1, KEi, Ni, -->
N(REDIRECTED_FROM, Initial_IP_R)
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ]
(IP_I:500 -> IP_R:500)
HDR(A,B), SK {IDi, [CERT,] [CERTREQ,]
[IDr,]AUTH, SAi2, TSi, TSr} -->
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}
When this mechanism is used with Mobile IPv6, a mobile node's
security associations with its home agent may expire while it still
has a valid binding cache entry at the home agent. In this case, the
mobile node MUST NOT use the original home agent address as the
destination address in the IKE_SA_INIT exchange to setup new security
associations. It MUST try to setup security associations with its
existing home agent.
4. Use of Anycast Addresses with the Redirect Mechanism
The use of anycast addresses will avoid having to configure a
particular VPN gateway's IP address in the DNS. Instead, the anycast
address that represents the group of VPN gateways is stored in the
DNS. When the VPN client performs a DNS lookup for the VPN gateway,
it receives the anycast address of the VPN gateway in the DNS
response.
If an anycast address is returned in response to DNS resolution of an
FQDN, the VPN client sends the IKE_SA_INIT request to the anycast
address. The IKE_SA_INIT request is routed to one of the VPN
gateways that is part of the anycast group. The VPN gateway that
receives the IKE_SA_INIT request responds with an IKE_SA_INIT reply
from the anycast address.
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Initiator Responder (any VPN GW)
--------- -------------------------
(IP_I:500 -> ANYCAST:500)
HDR(A,0), SAi1, KEi, Ni) -->
N(REDIRECT_SUPPORTED)
(ANYCAST:500 -> IP_I:500)
<-- HDR(A,0), N(REDIRECT, IP_R)
If the destination address on the IKE_SA_INIT request is an anycast
address, the VPN gateway that received the IKE_SA_INIT request MUST
include the REDIRECT payload to redirect the VPN client to a unicast
address of one of the VPN gateway. The VPN gateway that received the
IKE_SA_INIT request MAY redirect the client to its own unicast
address, if it is not overloaded.
The rest of the IKEv2 exchange is the same as described in Section 3.
5. Gateway Initiated Redirect
The redirect mechanism may also be used by a VPN gateway to redirect
the client to another VPN gateway in middle of a session. To
redirect a client, the gateway should send an INFORMATIONAL message
with the REDIRECT Notify payload. The REDIRECT payload MUST carry
information about the new VPN gateway. When the client receives this
message, it MUST send an empty message as an acknowledgement. Until
the client responds with an acknowledgement, the gateway SHOULD re-
transmit the redirect INFORMATIONAL message as described in [2]. The
following illustrates the INFORMATIONAL message exchange for gateway-
initiated redirect.
Initiator (VPN client) Responder (VPN GW)
---------------------- ------------------
<-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]}
HDR, SK {} -->
The INFORMATIONAL message exchange described above is protected by
the existing IKEv2 SA between the client and the gateway.
Once the client sends an acknowledgement to the gateway, it SHOULD
delete the existing security associations with the old gateway by
sending an Informational message with a DELETE payload. The gateway
MAY also decide to delete the security associations without any
signaling from the client, again by sending an Informational message
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with a DELETE payload. However, it should allow sufficient time for
the client to setup the required security associations with the new
security gateway. This time period should be configurable on the
gateway.
If the gateway decides to redirect the client during the IKE_AUTH
exchange, it prevents the creation of a CHILD SA by sending the
NO_ADDITIONAL_SAS Notify Payload in the IKE_AUTH response. It then
follows up with an INFORMATIONAL message with the REDIRECT payload
immediately. The following shows the message exchange between the
client and the gateway.
Initiator Responder ( VPN GW)
--------- -------------------
(IP_I:500 -> IP_R:500)
HDR(A,0), SAi1, KEi, Ni, -->
N(REDIRECTED_SUPPORTED)
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ]
(IP_I:500 -> IP_R:500)
HDR(A,B), SK {IDi, [CERT,] [CERTREQ,]
[IDr,]AUTH, SAi2, TSi, TSr} -->
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SK {IDr, [CERT,] AUTH,
N(NO_ADDITIONAL_SAS)}
<-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]}
HDR, SK {} -->
When the client receives the IKE_AUTH response with the
NO_ADDITIONAL_SAS payload from the gateway, it may decide to delete
the IKEv2 SA. In case the gateway receives the INFORMATIONAL message
to delete the IKEv2 SA before sending the REDIRECT message, then the
gateway includes the REDIRECT payload in the response along with the
DELETE payload.
6. Redirect Messages
6.1. REDIRECT_SUPPORTED
The REDIRECT_SUPPORTED payload is included in the initial IKE_SA_INIT
request by the initiator to indicate support for the IKEv2 redirect
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mechanism described in this document.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and
the 'Notify Message Type' fields are the same as described in Section
3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that
the SPI is not present in this message. The 'Protocol ID' should be
set to 0, since the notification is not specific to a particular
security association.
The 'Payload Length' field MUST be set to '8'. The 'Notify Message
Type' field is set to indicate the REDIRECT_SUPPORTED payload <value
to be assigned by IANA>.
6.2. REDIRECT
The REDIRECT payload is included in an IKE_SA_INIT response from the
responder or an INFORMATIONAL message from the responder, when the
responder wants to redirect the initiator to another VPN gateway.
The message includes the new responder's IP address.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GW Ident Type | |
+---------------+ ~
~ New Responder GW Identity ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and
the 'Notify Message Type' fields are the same as described in Section
3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that
the SPI is not present in this message. The 'Protocol ID' should be
set to 0, since the notification is not specific to a particular
security association.
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If the IP address of the new VPN gateway is sent, the 'Payload
Length' field MUST be set to either '13' or '25' depending on whether
an IPv4 or IPv6 address is sent in the message. If the FQDN of the
new VPN gateway is sent, the 'Payload Length' field is set to the
length of the FQDN plus the fixed fields in the message. The 'Notify
Message Type' field is set to indicate the REDIRECT payload <value to
be assigned by IANA>. The 'GW Identity Type' field indicates the
type of information that is sent to identify the new VPN gateway.
The following values are reserved by this document.
1 - IPv4 address of the new VPN gateway
2 - IPv6 address of the new VPN gateway
3 - FQDN of the new VPN gateway
All other values for this field are reserved and MUST NOT be used.
The identity of the new VPN gateway is carried in the 'New Responder
GW Identity' field.
6.3. REDIRECTED_FROM
The REDIRECTED_FROM message type is included in the IKE_SA_INIT
request from the initiator to the new VPN gateway to indicate the IP
address of the original VPN gateway that redirected the initiator.
The original VPN gateway's IP address is included in the message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GW Ident Type | |
+---------------+ ~
~ Original Responder GW Identity ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and
the 'Notify Message Type' fields are the same as described in Section
3.10 of [2] The 'SPI Size' field MUST be set to 0 to indicate that
the SPI is not present in this message. The 'Protocol ID' should be
set to 0, since the notification is not specific to a particular
security association.
The 'Payload Length' field MUST be set to either '13' or '25'
depending on whether an IPv4 or IPv6 address of the original VPN
gateway is sent in the message. The 'Notify Message Type' field is
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set to indicate the REDIRECTED_FROM payload <value to be assigned by
IANA>. The 'GW Identity Type' field indicates the type of
information that is sent to identify the new VPN gateway. The
following values are reserved by this document.
1 - IPv4 address of the original VPN gateway
2 - IPv6 address of the original VPN gateway
All other values for this field are reserved and MUST NOT be used.
The identity of the original VPN gateway is carried in the 'Original
Responder GW Identity' field.
7. Use of the Redirect Mechanism between IKEv2 Peers
The Redirect mechanism described in this document is mainly intended
for use in client-gateway scenarios. However, the mechanism can also
be used between any two IKEv2 peers. But this protocol is
asymmetric, meaning that only the original responder can redirect the
original initiator to another server.
8. Security Considerations
An eavesdropper on the path between VPN client and server may send a
redirect to the client upon receiving an IKE_SA_INIT message from
this client. This is no problem regarding DoS attacks for the VPN
connection, since an on-path-attacker can as well drop the
IKE_SA_INIT requests to prevent VPN access for the client. But an
eavesdropper on the path between VPN client and server can redirect a
large number of clients to a victim, which is then flooded with
IKE_SA_INIT requests. Flooding only happens if many clients initiate
IKEv2 exchange at almost the same time, which is considered a rare
event. However, this may happen if a Home Agent/VPN server is
shutdown for maintenance and all clients need to re-establish VPN
connections with another Home Agent/VPN server or if the on-path
attacker forces all IPsec security associations to expire by dropping
all received IKEv2 messages.
The use of REDIRECTED_FROM payload is intended to discourage a rogue
VPN gateway from redirecting a large number of VPN clients to a
particular VPN gateway. It does not prevent such a DoS attack.
9. IANA Considerations
This document defines four new IKEv2 Notification Message types as
described in Section 6. The three Notify Message Types must be
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assigned values between 16396 and 40959.
o REDIRECT_SUPPORTED
o REDIRECT
o REDIRECTED_FROM
10. Acknowledgements
The use of anycast address with IKEv2 was first described in [6]. It
was then added to an early draft version of RFC 5026 and later
removed before the RFC was published. Therefore the authors of [6]
and RFC 5026 are acknowledged.
Thanks to Pasi Eronen, with whom the solution described in this
document was extensively discussed. Thanks to Tero Kivinen for
suggesting the use of REDIRECTED_FROM payload and other comments
which helped improve the document. The authors would also like to
thank Yaron Sheffer, Sunil Kumar, Fan Zhao, Yoav Nir, Richard
Graveman, and Arnaud Ebalard for their reviews and comments.
11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306,
December 2005.
11.2. Informative References
[3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[4] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
Bootstrapping in Split Scenario", RFC 5026, October 2007.
[5] Haley, B., Devarapalli, V., Deng, H., and J. Kempf, "Mobility
Header Home Agent Switch Message", RFC 5142, January 2008.
[6] Weniger, K. and F. Dupont, "IKEv2-based Home Agent Assignment in
Mobile IPv6/NEMO Bootstrapping", draft-dupont-ikev2-haassign-02
(work in progress), January 2007.
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Authors' Addresses
Vijay Devarapalli
WiChorus
3590 North First St
San Jose, CA 95134
USA
Email: vijay@wichorus.com
Kilian Weniger
Email: kilian.weniger@googlemail.com
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