Internet DRAFT - draft-srivastava-sipping-loop-avoidance
draft-srivastava-sipping-loop-avoidance
SIPPING S. Srivastava
Internet-Draft Nortel Networks
Expires: November 25, 2006 May 24, 2006
Loop Avoidance Using Audits on Registration
draft-srivastava-sipping-loop-avoidance-00
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document proposes change in registration process of SIP for
avoiding installation of looped bindings spread across more than one
proxy. This version of the document broadly outlines the solution.
Exact details will be provided in the subsequent versions, as the
solution progresses.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Modified Call Flow . . . . . . . . . . . . . . . . . . . . 4
3.2. Audit Mechanism . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Querying Proxies For Bindings . . . . . . . . . . . . . 5
3.2.2. Loop Detection using MAX-FORWARDS . . . . . . . . . . . 5
3.3. Action after loop detection . . . . . . . . . . . . . . . . 5
3.4. Addition of Routes Administratively . . . . . . . . . . . . 6
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informational References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. 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 RFC 2119 [1].
2. Problem Statement
Looped bindings spread across more than one proxy with forking can
generate enormous SIP traffic and eventually bring down the SIP
network elements. ID.ietf-sip-fork-loop-fix [7] provides the details
about the problem scenario.
3. Solution
ID.campen-sipping-stack-loop-detect [8] fixes the problem by having a
light weight loop detection algorithm instead of using via branch
hash computation as specified in RFC 3261 [2]. As verification on
the contacts is not performed, it goes further in negotiating the
max-breadth as specified in ID.sparks-sipping-max-breadth [9] to
contain the amplification. This solution requires loop detection at
all proxies for all transactions.
Consent framework ID.sipping-consent-framework [10] doesn't deal with
the loop detection using audit mechanism defined in this document.
Consent framework enables to get the permission from the endpoint
before adding the bindings. An attacker can still install the looped
bindings by deliberately giving the permissions. It is better for
the SIP network elements to check for looped bindings defensively.
The proposed solution doesn't let the looped registrations to succeed
itself. It proposes to change the registration process as specified
in RFC 3261 [2].
When registrar receives a REGISTER message, it checks for the
validity of contact. It terminates the REGISTER transaction with
"202 Accepted" response. When it gets the result of the audit on the
contact specified in REGISTER, it notifies the endpoint the success/
failure of the REGISTER request using REG-EVENT package RFC3680 [3].
Solution requires extending reg-event package for including result of
audit.
It is assumed that registrar takes care of checking the loops within
itself before committing it to location database, i.e. While adding
binding A@abc -> B@abc, it searches the location database for B@abc
and checks for loop. This check can be performed before returning a
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final response to REGISTER request.
The use case of contacts spanning across multiple proxies is
follow-me kind of services, where forwarding is installed using
REGISTER. There is no need to run the audit on the contact in case
of
A)Register Refresh Request
B)UnRegister Request
C)Register Request where Contact in request doesn't point to
another proxy and AOR doesn't contain address of a physical device
In the above cases registrar does the normal processing as specified
in RFC 3261 [2]
3.1. Modified Call Flow
UA Proxy (P1) Proxy for Contact
in REGISTER (P2)
| | |
|-----REGISTER----->| |
| | |
|<---202 Accepted---| |
| | |
|<-NOTIFY (REG-EV)--| |
| | |
|--200 OK (NOTIFY)->| |
| | |
| |<--Audit on Contact in REGISTER--->|
| | |
|<-NOTIFY (REG-EV)--| |
| | |
|--200 OK (NOTIFY)->| |
| | |
Figure 1 Call Flow With Modified Registration Process
Above call flow is similar to REFER method processing as specified in
RFC3515 [5]. REGISTER transaction is terminated with "202 Accepted"
final response, as it gives ample time for auditing the contact. It
might be possible that audit process might consult multiple proxies
(e.g. AOR - Contact pair A->B , B->C ..... ). Here no of proxies
visited by default is 70 (MAX-FORWARDS default). It can be some
configurable value also. The second NOTIFY in the above call flow
will have the outcome of audit on the contact in REGISTER message.
The other alternative solution is return 1xx response on receipt of
REGISTER and then run the audit. This causes un-desirable effect due
to long Non-Invite-Transaction processing as specified in RFC4321 [6]
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3.2. Audit Mechanism
There are two possible mechanism for verifying the contacts in the
REGISTER message.
3.2.1. Querying Proxies For Bindings
If querying capability for third party registration is allowed at the
proxy (P2 in Figure 1) in contact header for the proxy in To header
(P1 in Figure 1) in REGISTER request, then registering proxy (P1) can
query proxy in contact header (P2) for the bindings. Then
Registering Proxy (P1) checks whether it is the target in binding
obtained from retargeting proxy (P2) with the same user, then it
treats as a loop. If it is destined for another proxy then it
queries that proxy and repeats the check. In the chain of proxies, a
proxy can ask other proxy to get the contacts on its behalf. It
assumes the transitive trust relationship, which may not be provided
by service provider.
3.2.2. Loop Detection using MAX-FORWARDS
Proxy can use increasing MAX-FORWARDS values with OPTIONS message to
find the loop from detailed information available in the 483 response
as specified in ID.ietf-sip-hop-limit-diagnostics [4].
3.3. Action after loop detection
If there is no loop found, registrar sends the "success" in REG-EVENT
NOTIFY, otherwise it sends the "failure" in REG-EVENT NOTIFY.
If loop is found due to addition of binding, a Registrar can take one
of the following actions for keeping the bindings
A)keep the contact in the location database but Proxy doesn't use
this for retargeting the further request unless loop is broken by
one of the proxies in the loop chain. If request comes to proxy
for retargeting in the looped contact time window, it rejects the
request with new error code "Loop Removal Needed". Appropriate
4xx code for this will be defined later.
B)reject the registration request and doesn't keep the binding.
Since these are looped bindings, it is difficult to decide which
binding in the looped chain will be deleted later. It is already
the error case, so it is better to reject the latest registration
which is causing the loop and let endpoints clean up its
associated registrations.
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OPEN ISSUE : Which option A) or B) should be chosen ?
3.4. Addition of Routes Administratively
When routes are added by administrator, it is expected from them to
run the loop detection audits before committing the routes to
location database.
4. Backward Compatibility
TBD
5. Security Considerations
TBD
6. IANA Considerations
TBD.
7. Acknowledgments
The author would like to thank Francois Audet and Meenakshi Kaushik
for providing valuable feedback. The author would like to thank
Robert Sparks and Dale Worley for providing valuable comments on the
mailing list while discussing the idea.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", RFC 3680, March 2004.
[4] Lawrence, S., "Diagnostic Responses for SIP Hop Limit Errors",
draft-ietf-sip-hop-limit-diagnostics-00 (work in progress),
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February 2006.
8.2. Informational References
[5] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[6] Sparks, R., "Problems Identified Associated with the Session
Initiation Protocol's (SIP) Non-INVITE Transaction", RFC 4321,
January 2006.
[7] Sparks, R., "Addressing an Amplification Vulnerability in
Forking Proxies", draft-ietf-sip-fork-loop-fix-01 (work in
progress), April 2006.
[8] Campen, B., "An Efficient Loop Detection Algorithm for SIP
Proxies", draft-campen-sipping-stack-loop-detect-00 (work in
progress), March 2006.
[9] Sparks, R., "Limiting the Damage from Amplification Attacks in
SIP Proxies", draft-sparks-sipping-max-breadth-00 (work in
progress), March 2006.
[10] Rosenberg, J., "A Framework for Consent-Based Communications in
the Session Initiation Protocol (SIP)",
draft-ietf-sipping-consent-framework-04 (work in progress),
March 2006.
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Author's Address
Samir Srivastava
Nortel Networks
4655 Great America Parkway
Santa Clara, CA 95054
US
Phone: +1 408 495 5143
Email: samirsr@nortel.com
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