Network Working Group V. Devarapalli
Internet-Draft WiChorus
Intended status: Standards Track K. Weniger
Expires: December 18, 2009 June 16, 2009
Redirect Mechanism for IKEv2
draft-ietf-ipsecme-ikev2-redirect-11.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. This document may contain material
from IETF Documents or IETF Contributions published or made publicly
available before November 10, 2008. The person(s) controlling the
copyright in some of this material may not have granted the IETF
Trust the right to allow modifications of such material outside the
IETF Standards Process. Without obtaining an adequate license from
the person(s) controlling the copyright in such materials, this
document may not be modified outside the IETF Standards Process, and
derivative works of it may not be created outside the IETF Standards
Process, except to format it for publication as an RFC or to
translate it into languages other than English.
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 Internet-Draft will expire on December 18, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Devarapalli & Weniger Expires December 18, 2009 [Page 1]
Internet-Draft IKEv2 Redirect June 2009
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
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.
Devarapalli & Weniger Expires December 18, 2009 [Page 2]
Internet-Draft IKEv2 Redirect June 2009
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IKEv2 Initial Exchange with Redirect . . . . . . . . . . . . . 4
4. Use of Anycast Addresses with the Redirect Mechanism . . . . . 6
5. Gateway Initiated Redirect . . . . . . . . . . . . . . . . . . 7
6. Redirect During IKE_AUTH Exchange . . . . . . . . . . . . . . 8
7. Using the Redirect Mechanism with Mobile IPv6 . . . . . . . . 9
8. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 10
8.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 10
8.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 12
9. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. Normative References . . . . . . . . . . . . . . . . . . . 15
13.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Devarapalli & Weniger Expires December 18, 2009 [Page 3]
Internet-Draft IKEv2 Redirect June 2009
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
gateway 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 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.
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 Initial Exchange with Redirect
This section describes the use of Redirect mechanism during the
IKE_SA_INIT exchange. Gateway-initiated redirect and the use of
redirect during IKE_AUTH exchange are explained in subsequent
sections.
The VPN client indicates support for the IKEv2 redirect mechanism and
the willingness to be redirected by including a REDIRECT_SUPPORTED
notification message in the initial IKE_SA_INIT request. (See
Section 8.1). The gateway MUST keep track of those clients that
indicated support for the redirect mechanism and those that didn't.
Devarapalli & Weniger Expires December 18, 2009 [Page 4]
Internet-Draft IKEv2 Redirect June 2009
To redirect an IKEv2 session to another VPN gateway, the VPN gateway
that initially received the IKE_SA_INIT request selects another VPN
gateway (how the selection is made is beyond the scope of this
document), and replies with an IKE_SA_INIT response containing a
REDIRECT notification message. (See Section 8.2). The notification
includes information about the selected VPN gateway, and the nonce
data from the Ni payload in the IKE_SA_INIT request. If the
IKE_SA_INIT request did not indicate support for the redirect
mechanism, the responder MUST NOT send the REDIRECT payload to the
VPN client. This is applicable to all REDIRECT scenarios described
in this document.
Note that when the IKE_SA_INIT response includes the REDIRECT
notification, the exchange does not result in the creation of an
IKE_SA and the responder SPI will be zero.
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, New_GW_ID, Ni_data)
When the client receives the IKE_SA_INIT response, it MUST verify
that the nonce data matches the value sent in the IKE_SA_INIT
request. If the values do not match, the client MUST silently
discard the response (and keep waiting for another response). This
prevents certain Denial-of-Service attacks on the initiator that
could be caused by an attacker injecting IKE_SA_INIT responses with
the REDIRECT payloads.
After verifying the nonce data, the client initiates a new
IKE_SA_INIT exchange with the VPN gateway listed in the REDIRECT
payload provided this is allowed by its PAD entries. In the
IKE_SA_INIT exchange with the new VPN gateway, the client MUST
include the REDIRECTED_FROM payload. (See Section 8.3). The VPN
client includes the IP address of the original VPN gateway that
redirected the client in the REDIRECTED_FROM notification. The IKEv2
exchange then proceeds as it would have proceeded with the original
VPN gateway.
Devarapalli & Weniger Expires December 18, 2009 [Page 5]
Internet-Draft IKEv2 Redirect June 2009
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}
The client MAY get redirected again by the new VPN gateway if the new
VPN gateway cannot also serve the client. The client does not have
to include the REDIRECT_SUPPORTED payload again in the IKE_SA_INIT
exchange with the new gateway after a redirect. The presence of the
REDIRECT_FROM payload in the IKE_SA_INIT exchange with the new
gateway indicates to the new gateway that the client supports the
redirect mechanism.
When the client gets redirected, it MUST use the same Peer
Authorization Database (PAD) and Security Policy Database (SPD)
entries as it would have used with the original gateway. Receiving a
redirect notification MUST NOT result in the modification of any PAD
or SPD entries. In practice, this means the new gateway either has
to use the same responder identity (IDr) as the original gateway, or
both should be part of a group of responders that are authorized by
the same PAD entry. See section 4.4.3.1 of [8] on using DNS names to
represent a group of peers in a PAD entry.
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
Devarapalli & Weniger Expires December 18, 2009 [Page 6]
Internet-Draft IKEv2 Redirect June 2009
address. The REDIRECT_SUPPORTED payload is included in the
IKE_SA_INIT request sent 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.
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, New_GW_ID, Ni_data)
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. The gateway MUST NOT include
any nonce data in the REDIRECT payload, since it is a gateway-
initiated message and is protected by the IKEv2 security association.
When the client receives this message, it sends a response (usually
empty) to the gateway. The gateway retransmits the redirect
INFORMATIONAL message as described in [2], until it gets a response.
The following illustrates the INFORMATIONAL message exchange for
gateway-initiated redirect.
Initiator (VPN client) Responder (VPN GW)
---------------------- ------------------
<-- HDR, SK {N(REDIRECT, New_GW_ID)}
HDR, SK {} -->
Devarapalli & Weniger Expires December 18, 2009 [Page 7]
Internet-Draft IKEv2 Redirect June 2009
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
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.
6. Redirect During IKE_AUTH Exchange
If the gateway decides to redirect the client during the IKE_AUTH
exchange, based on the identity presented by the client in the
IKE_AUTH request message, it prevents the creation of a CHILD SA and
sends the REDIRECT payload in the IKE_AUTH response. The gateway
MUST verify the client's AUTH payload before sending the Redirect
payload, and the client MUST verify the gateway's AUTH payload before
acting on the Redirect payload. Since the AUTH payloads were
exchanged and successfully verified, the IKEv2 security association
is valid. When the client receives the IKE_AUTH response with the
REDIRECT payload, it SHOULD delete the IKEv2 security association
with the gateway by sending an Informational message with a DELETE
payload.
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(REDIRECT, New_GW_ID)}
In case the IKE_AUTH exchange involves EAP authentication as
Devarapalli & Weniger Expires December 18, 2009 [Page 8]
Internet-Draft IKEv2 Redirect June 2009
described in Section 2.16 of RFC 4306 [2], or multiple authentication
methods as described in RFC 4739 [6], the gateway may decide to
redirect the client based on the interaction with the AAA server or
the external authentication server. In this case, the gateway MUST
send the REDIRECT Notification payload in either the first or the
last IKE_AUTH response. The client and the gateway MUST verify the
AUTH payloads as described above.
When EAP is used, the gateway MAY also redirect the client based on
the unauthenticated identity presented by the client in the first
IKE_AUTH exchange itself. Since EAP is used as the authentication
mechanism, the client does not include AUTH payload to authenticate
his identity, but the server still MUST include his own AUTH payload,
and client MUST verify it. Note that the IKEv2 SA is not created in
this case and the client does not have to explicitly delete the IKEv2
SA.
In all of the cases above, the client MUST accept the REDIRECT
notification only in the first IKE_AUTH response or the last IKE_AUTH
response. It MUST NOT accept the REDIRECT notification in an
intermediate IKE_AUTH response.
7. Using the Redirect Mechanism with Mobile IPv6
Mobile IPv6 [3] may use IKEv2 for mutual authentication between the
mobile node and the home agent, for home address configuration and
for setting up security associations for protecting Mobile IPv6
signaling messages [4]. The IKEv2 exchange, if IKEv2 is used,
precedes the exchange of Mobile IPv6 signaling messages. Therefore,
the mechanism described in this document can 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.
When running IKEv2 between a Mobile IPv6 Mobile Node (MN) and Home
Agent (HA), redirecting the IKEv2 exchange to another HA is not
enough; the Mobile IPv6 signalling also needs to be sent to the new
HA address. The MN MAY treat the information received in the
IKE_SA_INIT response in similar way as it would treat HA discovery
Devarapalli & Weniger Expires December 18, 2009 [Page 9]
Internet-Draft IKEv2 Redirect June 2009
information received from other unauthenticated (and potentially
untrustworthy) sources (such as DNS lookups not protected with
DNSSEC). However, if the MN has authenticated information about its
Home Agent, it MUST NOT be updated based on the IKE_SA_INIT response.
If the REDIRECT notification is received during the IKE_AUTH exchange
(after the HA has been authenticated; see Section 6), the MN MAY pass
the new address to Mobile IPv6 and treat it in similar fashion as
information from the Home Agent Switch Message [5].
Gateway-initiated REDIRECT notifications exchanged in INFORMATIONAL
exchanges (see Section 5) MUST NOT result in updating any Mobile IPv6
state. In such cases, the Home Agent Switch Message specified in [5]
is used instead.
8. Redirect Messages
8.1. 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
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(=0)| 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' MUST be
set to 0, since the notification is not specific to a particular
security association.
The 'Payload Length' field is set to the length in octets of the
entire payload, including the generic payload header. The 'Notify
Message Type' field is set to indicate the REDIRECT_SUPPORTED payload
<value to be assigned by IANA>.
8.2. REDIRECT
The REDIRECT payload is included in an IKE_SA_INIT response from the
responder or an INFORMATIONAL message from the responder, when the
Devarapalli & Weniger Expires December 18, 2009 [Page 10]
Internet-Draft IKEv2 Redirect June 2009
responder wants to redirect the initiator to another VPN gateway.
The message includes the new responder's IP address or DNS name.
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(=0)| SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GW Ident Type | GW Ident Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ New Responder GW Identity ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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' MUST be
set to 0, since the notification is not specific to a particular
security association.
The 'Payload Length' field is set to the length in octets of the
entire payload, including the generic payload header. '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 valid in the REDIRECT payload.
1 - IPv4 address of the new VPN gateway
2 - IPv6 address of the new VPN gateway
3 - FQDN of the new VPN gateway
The 'GW Ident Len' field is set to the length of the gateway identity
information. The identity of the new VPN gateway is carried in the
'New Responder GW Identity' field. The IPv4 address, the IPv6
address or the FQDN of the new VPN gateway MUST be encoded as
described in section 3.5 of [2].
The 'Nonce Data' field carries the nonce data from the Ni payload
sent by the initiator. The size of the nonce MUST be between 16 and
256 bytes as described in Section 3.9 of [2]. The 'Nonce Data' field
is present in the REDIRECT payload only when the REDIRECT payload is
Devarapalli & Weniger Expires December 18, 2009 [Page 11]
Internet-Draft IKEv2 Redirect June 2009
sent in the IKE_SA_INIT response message. It MUST NOT be included in
the REDIRECT payload if sent in an IKE_AUTH response or in a gateway-
initiated redirect message.
8.3. REDIRECTED_FROM
The REDIRECTED_FROM notification payload 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. This payload also serves the purpose of indicating
support for the redirect mechanism to the new VPN gateway after a
redirect.
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(=0)| SPI Size (=0) | Notify Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GW Ident Type | GW Ident Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
~ 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' MUST be
set to 0, since the notification is not specific to a particular
security association.
The 'Payload Length' field is set to the length in octets of the
entire payload, including the generic payload header. The 'Notify
Message Type' field is 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 valid in the REDIRECTED_FROM
payload.
1 - IPv4 address of the original VPN gateway
2 - IPv6 address of the original VPN gateway
The 'GW Ident Len' field is set to the length of the gateway identity
information. The identity of the original VPN gateway is carried in
the 'Original Responder GW Identity' field.
Devarapalli & Weniger Expires December 18, 2009 [Page 12]
Internet-Draft IKEv2 Redirect June 2009
9. 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.
10. 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.
The redirect mechanism MUST NOT update any state on the client apart
from the VPN gateway information. When used with Mobile IPv6, care
must be taken to ensure that the home agent information that the
mobile node has configured is not modified wrongly by the redirect
message.
The client could end up getting redirected multiple times in a
sequence, either because of wrong configuration or a DoS attack. The
client could even end up in a loop with two or more gateways
redirecting the client to each other. This could deny service to the
client. To prevent this, the client should be configured not to
accept more a certain number of redirects within a short time period.
This should be configurable on the client.
Redirecting based on the unauthenticated identities from the client
might leak out information about the user when an active attacker,
pretending to be a VPN client can get information to which gateway
the real user was redirected to. If redirection is based on some
Devarapalli & Weniger Expires December 18, 2009 [Page 13]
Internet-Draft IKEv2 Redirect June 2009
internal information of the user, it might leak information to
attacker about the user which might not available otherwise. To
prevent these kind of attacks, redirection based on unauthenticated
ID should be avoided and should be done only after the client has
also authenticated itself.
11. IANA Considerations
This document defines three new IKEv2 Notification Message types as
described in Section 8. The three Notify Message Types must be
assigned values between 16396 and 40959.
o REDIRECT_SUPPORTED
o REDIRECT
o REDIRECTED_FROM
This document creates a new namespace called the "Gateway Identity
Type". This is used to indicate the type of information regarding
the VPN gateway that is carried in the REDIRECT (Section 8.2) and
REDIRECTED_FROM (Section 8.3) Notification payloads. The following
values are assigned.
1 - IPv4 address of the new VPN gateway
2 - IPv6 address of the new VPN gateway
3 - FQDN of the new VPN gateway
Values '0', and 4-240 are reserved. New values can be allocated by
Expert Review [9]. Values 241-255 are set aside for private use. A
specification that extends this registry MUST also mention which of
the new values are valid in which Notification payload.
12. Acknowledgements
The use of anycast address with IKEv2 was first described in [7]. It
was then added to an early draft version of RFC 5026 and later
removed before the RFC was published. Therefore the authors of [7]
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, Kanagavel Rajan, Srini Addepalli, Raj Singh, and Arnaud
Ebalard for their reviews and comments.
Devarapalli & Weniger Expires December 18, 2009 [Page 14]
Internet-Draft IKEv2 Redirect June 2009
13. References
13.1. 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.
13.2. 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] Eronen, P. and J. Korhonen, "Multiple Authentication Exchanges
in the Internet Key Exchange (IKEv2) Protocol", RFC 4739,
November 2006.
[7] 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.
[8] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
Authors' Addresses
Vijay Devarapalli
WiChorus
3590 North First St
San Jose, CA 95134
USA
Email: vijay@wichorus.com
Devarapalli & Weniger Expires December 18, 2009 [Page 15]
Internet-Draft IKEv2 Redirect June 2009
Kilian Weniger
Email: kilian.weniger@googlemail.com
Devarapalli & Weniger Expires December 18, 2009 [Page 16]
