Network Working Group Y. Xu
Internet-Draft Tsinghua Univ.
Intended status: Standards Track P. Yang
Expires: January 8, 2009 Y. Ma
Hitachi (China) R&D Corporation
H. Deng
China Mobile
K. Xu
Tsinghua University
July 7, 2008
IKE SA Synchronization
draft-xu-ike-sa-sync-00
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Abstract
It will take a long time to do security association syncronization
among IKE/IPsec gateways possibly maintaining huge numbers of IKEv2/
IPsec SAs. The major reason is that the prcocedure of IKEv2 SA re-
establishment will incur a time-consuming computation especially in
the Diffie-Hellman exchange. In this draft, a new IKE security
associations synchronization solution is proposed to reduce the
computation by directly transferring the indexed IKE SA from old
gateway to new gateway, wherein the most expensive Diffie-Hellman
calculation can be avoided. Without some time-consuming IKEv2
exchanges, the huge amount of IKE/IPsec SA synchronization procedures
can be finished in a short time.
Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Application scenarios . . . . . . . . . . . . . . . . . . . . 4
2.1. Scenario of failover . . . . . . . . . . . . . . . . . . . 4
2.2. Scenario of load-balance . . . . . . . . . . . . . . . . . 5
3. Details on Proposed solution . . . . . . . . . . . . . . . . . 6
3.1. Overview of the Proposed solution . . . . . . . . . . . . 6
3.2. Key data structure . . . . . . . . . . . . . . . . . . . . 6
3.3. Consideration on Stub handling . . . . . . . . . . . . . . 7
3.4. Consideration on location of Stub . . . . . . . . . . . . 8
3.5. When should Gateways download/update Stub . . . . . . . . 9
3.6. Related new messages . . . . . . . . . . . . . . . . . . . 9
4. Modification on the base IKEv2 protocol . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Normative References . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Background
IKEv2 protocol which has been defined by rfc4306[1] provides us a
method to negotiate ipsec's key automatically between ipsec clients
and gateway. Before negotiating ipsec's key, they should negotiate
IKE's SA first. Usually, ipsec client sends IKE_INIT message to
gateway with SAi1, KEi, Ni, then gateway chooses some proposal of
SAi1 which come to the algorithm for encryption and decryption, also
proposal for Diffie-Hellman, and then calculates the Diffie-Hellman,
sends IKE_INIT respond message back to ipsec client. At this time,
the most important keyring can be generated. After other IKE_AUTH
exchange, each other has verified the identity. IKE SA has
completely been established.
Initiator Responder
----------- -----------
HDR, SAi1, KEi, Ni -->
< -- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERT,]
[CERTREQ,] [IDr,],AUTH,
SAi2, TSi, TSr} -->
< -- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}
Figure 1: IKE_INIT and IKE_AUTH exchanges
But it seems too time consuming to establish an IKE SA in these first
two exchanges, especially Diffie-Hellman computation, as we know it
is too slow to compute, so it is a challenge to the new gateway when
thousands of, even more, ipsec clients are transfered from old
gateway to new the gateway.
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2. Application scenarios
2.1. Scenario of failover
IPsec old new/old
client Gateway gateway
| | |
| IKE/IPsec SAs | |
|< ========================== >| |
| | |
| | |
| O Fail of old GW |
| | |
O detect the fail | |
| of old GW | |
| | |
| new IKE init procedure |
|< =================================================== >|
| | |
| set up other child IPsec SAs |
|< =================================================== >|
| | |
Figure 2: failover scenarios
In this scenario, ipsec clients has established IKE connections with
old gateway, then for some reason, old gateway fails, after a short
time, ipsec client knows old gateway has failed(how to know gateway
fail is out of our scope), and reconnect to the old gateway or
another new gateway. It must be a rush hour, so many ipsec clients
connect to the gateway in the same time, as we know, re-establish IKE
security associations(SAs) is too slow to compute because of Diffie-
Huffman(DH). The problem statement and goals for a failover solution
are described in [2].
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2.2. Scenario of load-balance
IPsec old new
client Gateway gateway
| | |
| IKE/IPsec SAs | |
|< ========================== >| |
| | |
| | |
| O overload of old GW |
| | |
O detect the overload | |
| of old GW | |
| | |
| new IKE init procedure |
|< =================================================== >|
| | |
| set up other child IPsec SAs |
|< =================================================== >|
| | |
Figure 3: load-balance scenarios
In this scenario, after establishing IKE connections between ipsec
clients and old gateway, old gateway may not fail, owing to traffic
engineer or old gateway is over-loading, ipsec clients knows they
should stop the connection with old gateway and establish the
connection with new gateway(how to know new gateway is also out of
our scope). If many ipsec clients are transferd from old gateway to
new gateway, as same as failover, it is a challenge to new gateway to
establish IKE SA in the same time.
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3. Details on Proposed solution
3.1. Overview of the Proposed solution
In this section, we define a new data structure stub which has the
most important information of IKE SA, and gateway can use this data
structure to fast rebuild IKE SA. We expand the IKE_INIT exchange,
and add a payload called IKE_SA_SYN. because old gateway's IP address
and SPI can index the unique stub of IKE SA, so we make them in SYN
payload to index stub.
Initiator Responder
----------- --------------
HDR, SAi1, KEi, Ni, [SYN] --->
< -- HDR, Nr
Figure 4: IKE SA synchronization exchange
Once ipsec client has to be transfer from old gateway to new gateway,
it can send IKE_INIT which is extended a SYN payload as optional, the
IKE SYN payload has some index informatin such as old gateway ip
address and old gateway's SPI, if old/new gateway finds IKE_SA_SYN
payload in the IKE_INIT message, it can fast re-establish IKE SA
without DH computation and IKE_AUTH exchange, and IKE_INIT respond
with olny Nr to ipsec client to tell it IKE_SA has been re-
established. If new gateway does not support IKE_SA_SYN or not find
the proper stub, it can establish IKE SA by IKE_INIT and IKE_AUTH
exchanges, or just drop the packet.
3.2. Key data structure
the stub data structure should conclude all these informations. (We
have referenced "ticket" proposal[3].)
o IDi, IDr.
o SPIi, SPIr.
o SAr (the accepted proposal).
o SK_d.
o shared secret.
o old gateway's ip address.
We propose using c++ STL map data structure to store this stub
message, use old gateway's ip address and SPI as key, and the other
properties as value. You also can use other data structure to hash
old gateway's ip address and SPI to other properties.
SAr have the encrypt and decrypt algorithm, and shared secrect is the
DH exchange's result, we can calculate the IKE SA's keyring as rekey
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process. It will be very quick.
3.3. Consideration on Stub handling
1) generation
When IKE SA has been established(after first two exchanges), the
gateway extracts the stub from IKE SA and store it.
2) propagation
After extrcted from IKE SA, stubs should be updated to infrastructure
such as stub bank(we will define next section) or other gateway.
3) look-up
As the old gateway's ip address and spi can index the unique stub.
Such as map data structure, hash operation is very light-weighted,
you can find it very fast.
4) usage
In some senarios, the ipsec clients want to synchrinazation IKE SA
with a gateway. Then the ipsec clients send IKE_INIT message with
SYN payload to old/new gateway, gateway will get old gateway's IP
address and SPI from IKE_SA SYN payload, and find the stub in local
machine database (maybe download the stub from other gateway or stub
bank before), then rebuild the IKE SA. If IKE SA has been
established, gateway sends IKE_INIT respond(only conclude HDR and Nr)
to ipsec client. then create-child-sa exchanges, and so on.
The following signaling shall be supported by IKE/IPsec gateways to
communicate with Stub.
o Update Stub:
Gateway updates its stub to infrastructure once new stub has been
established, and the infrastructure store them by gateway's IP
address and SPI in a hash data structure.
o GET Stub:
Gateway receives IKE_SA SYN payload, then it send GET Stub to ask for
some stubs, the infrastructure index the stubs.
o Download Stub:
After infrastructure finds the stubs, it pushs the stubs to gateway.
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3.4. Consideration on location of Stub
1. Centralized infrastructure
ipsec old/new stub
client gateway bank
|| || Update Stub ||
|| HDR,SAi1,KEi,Ni,SYN||------------------->||
||------------------->|| GET Stub ||
||< ------------------||------------------->||
|| HDR,Nr || Download Stub ||
|| ||< ------------------||
|| || ||
Figure 5: centralized structure
This proposal has a centralized Stub Bank server, gateway doesn't
need local stub database.
a) After IKE connection has been established, old gateway update the
stub to stub bank.
b) Once transferring ipsec from old gateway to old/new gateway, ipsec
client send IKE_INIT with SYN payload.
c) When old/new gateway receives IKE_INIT with SYN payload, it ask
Stub Bank for stub via GET Stub signaling.
d) stub bank push proper stub to old/new gateway.
old/new gateway find the proper stub and rebuild IKE SA, then send
HDR, Nr to tell ipsec client that it has accepted the stub.
2. Distributed infrastructure
ipsec old/new Old GW
client gateway Stub
|| || ||
|| HDR,SAi1,KEi,Ni,SYN|| Update Stub ||
||------------------->||< ------------------||
||< ------------------|| ||
|| HDR,Nr || ||
Figure 6: distributed structure
This structure doesn't have centralized Stub Bank, and all gateway
must have local stub database, if there is stub in local database, it
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will find the stub in local database, otherwise, it will GET the stub
from other gateway.
a) After IKE connection has been established, old gateway update the
stub to stub bank.
b) Once transferring ipsec from old gateway to old/new gateway, ipsec
client send IKE_INIT with SYN payload.
c) old/new gateway find the proper stub and rebuild IKE SA, then send
HDR, Nr to tell ipsec client that it has accepted the stub.
Gateway has to store stubs in distributed structure, but it seems
more simple than centralized structure. Also, these two proposals
can mix together, other gateway also can be Stub Bank.
3.5. When should Gateways download/update Stub
Because of the stub is not sensitive with time, we can assemble the
stub messages to reduce the message number in update event.
The single gateway can get many stubs at a time in download event.
The gateway may also update the stubs in bundles whenever it was
thought to be necessary
3.6. Related new messages
1)IKE_SA_SYN Payload format
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GateWay's SPI |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GateWay's IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
C bit is the direction of this message.
2) Stub related signaling
Header Format
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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| type | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
type number
update 01
get 10
download 11
reserved 00
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| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| PAYLOAD CONTENT |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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4. Modification on the base IKEv2 protocol
As our principle, The base IKEv2 protocol should be changed as little
as possible. In the proposal, three aspects require slight
modification on IKEv2 protocol
1) new IKE message: IKE_SA_SYN
2) modification on the state machine
As ipsec client, it can send IKE_INIT message with SYN payload as
usual, and if it receives IKE_INIT respond only have Nr, it will
calculate the new ike sa like rekey. And set state to ike sa has
been established.
As gateway, once receives IKE_SA_SYN payload, will firstly find the
proper stub, if find the stub, it will fast re-establish IKE SA, send
IKE_INIT respond with Nr only to ipsec client, and set state to ike
sa has been established.
3) The gateway should support the Stub related functions like
extract_stub, update_stub and get_stub
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5. Security Considerations
the security framework of IKEv2 protocol will not be compromised in
this solution.
1) index is a light-weighted operation, and no stub, no response.
2) The Gateway can use SAr1, KEi to verify the identity, such as ID
property. But it depends on the configuration of operators.
3) Even if the index is right, ipsec client cannot rebuild IKE_SA,
the communication can't last, after a little time, the IKE_SA in
gateway will be deleted.
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6. Conclusion
In this draft, a new solution is proposed to do IKE SA
synchrinization for fast re-establishment of IKE SA. It will remove
the most time-consuming IKEv2 exchanges, which makes it much faster
to transfer millions of ipsec clients from old gateway to old/new
gateway. And the proposal in this draft will only slightly modify
the base IKEv2 protocol with a new logical IKE SA Stub in the
network.
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7. Normative References
[Narayanan06]
Narayanan, V., "IPsec Gateway Failover and Redundancy
Problem Statement and Goals",
draft-vidya-ipsec-failover-ps-00.txt (work in progress),
December 2006.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[Sheffer07]
Xie, Y., "Stateless Session Resumption for the IKE
Protocol", draft-sheffer-ike-session-resumption-00.txt
(work in progress), January 2007.
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Authors' Addresses
Yan Xu
Tsinghua Univ.
Department of Computer Science
Tsinghua University
Haidian District
Beijing, 100088
P.R. China
Email: xydkl@163.com
Peng Yang
Hitachi (China) R&D Corporation
301, North Wing, Tower C Raycom Infotech Park
2 kexueyuan Nanlu
Haidian District
Beijing, 100080
P.R. China
Phone: +861082862918(ext.)328
Email: pyang@hitachi.cn
Yuanchen Ma
Hitachi (China) R&D Corporation
301, North Wing, Tower C Raycom Infotech Park
2 kexueyuan Nanlu
Haidian District
Beijing, 100080
P.R. China
Phone: +861082862918(ext.)327
Email: ycma@hitachi.cn
Hui Deng
China Mobile
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Xu Ke
Tsinghua University
Department of Computer Science
Tsinghua University
Haidian District
Beijing, 100088
P.R. China
Email: xuke@mail.tsinghua.edu.cn
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