SIPCORE Working Group C. Holmberg
Internet-Draft Ericsson
Intended status: Standards Track December 9, 2010
Expires: June 12, 2011
Indication of support for keep-alive
draft-ietf-sipcore-keep-09.txt
Abstract
This specification defines a new Session Initiation Protocol (SIP)
Via header field parameter, "keep", which allows adjacent SIP
entities to explicitly negotiate usage of the Network Address
Translation (NAT) keep-alive mechanisms defined in SIP Outbound, in
cases where SIP Outbound is not supported, cannot be applied, or
where usage of keep-alives is not implicitly negotiated as part of
the SIP Outbound negotiation.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 12, 2011.
Copyright Notice
Copyright (c) 2010 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Use-case: Dialog from non-registered UAs . . . . . . . . . 3
1.2. Use-case: SIP Outbound not supported . . . . . . . . . . . 3
1.3. Use-case: SIP dialog initiated Outbound flows . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. User Agent and Proxy behavior . . . . . . . . . . . . . . . . 4
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Lifetime of keep-alives . . . . . . . . . . . . . . . . . 5
4.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.2. Keep-alives associated with registration . . . . . . . 5
4.2.3. Keep-alives associated with dialog . . . . . . . . . . 6
4.3. Behavior of a SIP entity willing to send keep-alives . . . 6
4.4. Behavior of a SIP entity willing to receive keep-alives . 7
5. Keep-alive frequency . . . . . . . . . . . . . . . . . . . . . 8
6. Connection reuse . . . . . . . . . . . . . . . . . . . . . . . 9
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Keep-alive negotiation associated with registration:
UA-proxy . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.3. Keep-alive negotiation associated with dialog: UA-proxy . 11
7.4. Keep-alive negotiation associated with dialog: UA-UA . . . 12
8. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. keep . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 17
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
13.1. Normative References . . . . . . . . . . . . . . . . . . . 17
13.2. Informative References . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
Section 3.5 of SIP Outbound [RFC5626] defines two keep-alive
mechanisms. Even though the keep-alive mechanisms are separated from
the rest of the SIP Outbound mechanism, SIP Outbound does not define
a mechanism to explicitly negotiate usage of the keep-alive
mechanisms. In some cases usage of keep-alives can be implicitly
negotiated as part of the SIP Outbound negotiation.
However, there are SIP Outbound use-cases where usage of keep-alives
is not implicitly negotiated as part of the SIP Outbound negotiation.
In addition, there are cases where SIP Outbound is not supported, or
where it cannot be applied, but where there is still a need to be
able to negotiate usage of keep-alives. Last, [RFC5626] only allows
keep-alives to be negotiated between a UA and an edge proxy, and not
between other SIP entities.
This specification defines a new Session Initiation Protocol (SIP)
[RFC3261] Via header field parameter, "keep", which allows adjacent
SIP entities to explicitly negotiate usage of the NAT keep-alive
mechanisms defined in SIP Outbound. The "keep" parameter allows SIP
entities to indicate willingness to send keep-alives, to indicate
willingness to receive keep-alives, and for SIP entities willing to
receive keep-alives to provide a recommended keep-alive frequency.
The following sections describe use-cases where a mechanism to
explicitly negotiate usage of keep-alives is needed.
1.1. Use-case: Dialog from non-registered UAs
In some cases a User Agent Client (UAC) does not register itself
before it establishes a dialog, but in order to maintain NAT bindings
open during the lifetime of the dialog it still needs to be able to
negotiate sending of keep-alives towards its adjacent downstream SIP
entity. A typical example is an emergency call, where a registration
is not always required in order to make the call.
1.2. Use-case: SIP Outbound not supported
In some cases all SIP entities that need to be able to negotiate the
usage of keep-alives might not support SIP Outbound. However, they
might still support the keep-alive mechanisms defined in SIP
Outbound, and need to be able to negotiate usage of them.
1.3. Use-case: SIP dialog initiated Outbound flows
SIP Outbound allows the establishment of flows using the initial
request for a dialog. As specified in [RFC5626], usage of keep-
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alives is not implicitly negotiated for such flows.
2. Conventions
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 BCP 14, RFC 2119
[RFC2119].
3. Definitions
Edge proxy: As defined in [RFC5626], a SIP proxy that is located
topologically between the registering User Agent (UA) and the
Authoritative Proxy.
NOTE: In some deployments the edge proxy might physically be located
in the same SIP entity as the Authoritative Proxy.
Keep-alives: The keep-alive messages defined in SIP Outbound
[RFC5626].
"keep" parameter: A SIP Via header field parameter that a SIP entity
can insert in the topmost Via header field that it adds to the
request, to explicitly indicate willingness to send keep-alives
towards its adjacent downstream SIP entity. A SIP entity can add a
parameter value to the "keep" parameter in a response to explicitly
indicate willingness to receive keep-alives from its adjacent
upstream SIP entity.
SIP entity: SIP User Agent (UA), or proxy, as defined in [RFC3261].
Adjacent downstream SIP entity: The adjacent SIP entity in the
direction towards which a SIP request is sent.
Adjacent upstream SIP entity: The adjacent SIP entity in the
direction from which a SIP request is received.
4. User Agent and Proxy behavior
4.1. General
This section describes how SIP UAs and proxies negotiate usage of
keep-alives associated with a registration, or a dialog, which types
of SIP requests can be used in order to negotiate the usage, and the
lifetime of the negotiated keep-alives.
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SIP entities indicate willingness to send keep-alives towards the
adjacent downstream SIP entity using SIP requests. The associated
responses are used by SIP entities to indicate willingness to receive
keep-alives. SIP entities that indicate willingness to receive keep-
alives can provide a recommended keep-alive frequency.
The procedures to negotiate usage of keep-alives are identical for
SIP UAs and proxies.
In general, it can be useful for SIP entities to indicate willingness
to send keep-alives, even if they are not aware of any necessity for
them to send keep-alives, since the adjacent downstream SIP entity
might have knowledge about the necessity. Similarly, if the adjacent
upstream SIP entity has indicated willingness to send keep-alives, it
can be useful for SIP entities to indicate willingness to receive
keep-alives, even if they are not aware of any necessity for the
adjacent upstream SIP entity to send them.
NOTE: Usage of keep-alives is negotiated per direction. If a SIP
entity has indicated willingness to receive keep-alives from an
adjacent SIP entity, sending of keep-alives towards the same SIP
entity needs to be separately negotiated.
NOTE: Since there are SIP entities that already use a combination of
Carriage Return and Line Feed (CRLF) as keep-alive messages, and SIP
entities are expected to be able to receive those, this specification
does not forbid the sending of double-CRLF keep-alive messages
towards an adjacent SIP entity even if usage of keep-alives with that
SIP entity has not been negotiated. However, the "keep" parameter is
still important in order for a SIP entity to indicate that it
supports sending of double-CRLF keep-alive messages, so that the
adjacent downstream SIP entity does not use other mechanisms (e.g.
short registration refresh intervals) in order to keep NAT bindings
open.
4.2. Lifetime of keep-alives
4.2.1. General
The lifetime of negotiated keep-alives depends on whether the keep-
alives are associated with a registration or a dialog. This section
describes the lifetime of negotiated keep-alives.
4.2.2. Keep-alives associated with registration
SIP entities use a registration request in order to negotiate usage
of keep-alives associated with a registration. Usage of keep-alives
can be negotiated when the registration is established, or later
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during the registration. Once negotiated, keep-alives are sent until
the registration is terminated, or until a subsequent registration
refresh request is sent or forwarded. When a subsequent registration
refresh request is sent or forwarded, if a SIP entity is willing to
continue sending keep-alives associated with the registration, usage
of keep-alives MUST be re-negotiated. If usage is not successfully
re-negotiated, the SIP entity MUST cease sending of keep-alives
associated with the registration.
4.2.3. Keep-alives associated with dialog
SIP entities use an initial request for a dialog, or a mid-dialog
target refresh request [RFC3261], in order to negotiate sending and
receiving of keep-alives associated with a dialog. Usage of keep-
alives can be negotiated when the dialog is established, or later
during the lifetime of the dialog. Once negotiated, keep-alives MUST
be sent for the lifetime of the dialog, until the dialog is
terminated. Once usage of keep-alives associated with a dialog has
been negotiated, it is not possible to re-negotiate the usage
associated with the dialog.
4.3. Behavior of a SIP entity willing to send keep-alives
As defined in [RFC5626], a SIP entity that supports sending of keep-
alives must act as a Session Traversal Utilities for NAT (STUN)
client [RFC5389]. The SIP entity must support those aspects of STUN
that are required in order to apply the STUN keep-alive mechanism
defined in [RFC5626], and it must support the CRLF keep-alive
mechanism defined in [RFC5626]. [RFC5626] defines when to use STUN,
respectively double-CRLF, for keep-alives.
When a SIP entity sends or forwards a request, if it wants to
negotiate the sending of keep-alives associated with a registration,
or a dialog, it MUST insert a "keep" parameter in the topmost Via
header field that it adds to the request, to indicate willingness to
send keep-alives.
When the SIP entity receives the associated response, if the "keep"
parameter in the topmost Via header field of the response contains a
"keep" parameter value, it MUST start to send keep-alives towards the
same destination where it would send a subsequent request (e.g.
REGISTER requests and initial requests for dialog) associated with
the registration (if the keep-alive negotiation is for a
registration), or where it would send subsequent mid-dialog requests
(if the keep-alive negotiation is for a dialog). Subsequent mid-
dialog requests are addressed based on the dialog route set.
Once a SIP entity has negotiated sending of keep-alives associated
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with a dialog towards an adjacent SIP entity, it MUST NOT insert a
"keep" parameter in any subsequent SIP requests, associated with the
dialog, towards that adjacent SIP entity. Such "keep" parameter MUST
be ignored, if received.
Since an ACK request does not have an associated response, it can not
be used to negotiate usage of keep-alives. Therefore, a SIP entity
MUST NOT insert a "keep" parameter in the topmost Via header field of
an ACK request. Such "keep" parameter MUST be ignored, if received.
A SIP entity MUST NOT indicates willingness to send keep-alives
associated with a dialog, unless it has also inserted itself in the
dialog route set [RFC3261].
NOTE: When a SIP entity sends an initial request for a dialog, if the
adjacent downstream SIP entity does not insert itself in the dialog
route set using a Record-Route header field [RFC3261], the adjacent
downstream SIP entity will change once the dialog route set has been
established. If a SIP entity inserts a "keep" parameter in the
topmost Via header field of an initial request for a dialog, and the
"keep" parameter in the associated response does not contain a
parameter value, the SIP entity might choose to insert a "keep"
parameter in the topmost Via header field of a subsequent SIP request
associated with the dialog, in case the new adjacent downstream SIP
entity (based on the dialog route set) is willing to receive keep-
alives (in which case it will add a parameter value to the "keep"
parameter).
If an INVITE request is used to indicate willingness to send keep-
alives, as long as at least one response (provisional or final) to
the INVITE request contains a "keep" parameter with a parameter
value, it is seen as an indication that the adjacent downstream SIP
entity is willing to receive keep-alives associated with the dialog
on which the response is received.
4.4. Behavior of a SIP entity willing to receive keep-alives
As defined in [RFC5626], a SIP entity that supports receiving of
keep-alives must act as a STUN server [RFC5389]. The SIP entity must
support those aspects of STUN that are required in order to apply the
STUN keep-alive mechanism defined in [RFC5626], and it must support
the CRLF keep-alive mechanism defined in [RFC5626].
When a SIP entity sends or forwards a response, and the adjacent
upstream SIP entity indicated willingness to send keep-alives, if the
SIP entity is willing to receive keep-alives associated with the
registration, or the dialog, from the adjacent upstream SIP entity it
MUST add a parameter value to the "keep" parameter, before sending or
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forwarding the response. The parameter value, if present and with a
value other than zero, represents a recommended keep-alive frequency,
given in seconds.
There might be multiple responses to an INVITE request. When a SIP
entity indicates willingness to receive keep-alives in a response to
an INVITE request, it MUST add a parameter value to the "keep"
parameter in at least one reliable response to the request. The SIP
entity MAY add identical parameter values to the "keep" parameters in
other responses to the same request. The SIP entity MUST NOT add
different parameter value to the "keep" parameters in responses to
the same request. The SIP entity SHOULD indicate the willingness to
receive keep-alives as soon as possible.
A SIP entity MUST NOT indicates willingness to receive keep-alives
associated with a dialog, unless it has also inserted itself in the
dialog route set [RFC3261].
5. Keep-alive frequency
If a SIP entity receives a SIP response, where the topmost Via header
field contains a "keep" parameter with a non-zero value that
indicates a recommended keep-alive frequency, given in seconds, it
MUST use the procedures defined for the Flow-Timer header field
[RFC5626]. According to the procedures, the SIP entity must send
keep-alives at least as often as the indicated recommended keep-alive
frequency, and if the SIP entity uses the recommended keep-alive
frequency then it should send its keep-alives so that the interval
between each keep-alive is randomly distributed between 80% and 100%
of the recommended keep-alive frequency.
If the received "keep" parameter value is zero, the SIP entity can
send keep-alives at its discretion. [RFC5626] provides additional
guidance on selecting the keep-alive frequency in case a recommended
keep-alive frequency is not provided.
This specification does not specify actions to take if negotiated
keep-alives are not received. As defined in [RFC5626], the receiving
SIP entity may consider a connection to be dead in such situations.
If a SIP entity that adds a parameter value to the "keep" parameter,
in order to indicate willingness to receive keep-alives, also inserts
a Flow-Timer header field (that can happen if the SIP entity is using
both the Outbound mechanism and the keep-alive mechanism) in the same
SIP message, the header field value and the "keep" parameter value
MUST be identical.
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SIP Outbound uses the Flow-Timer header field to indicate the server-
recommended keep-alive frequency. However, it will only be sent
between a UA and an edge proxy. Using the "keep" parameter, however,
the sending and receiving of keep-alives might be negotiated between
multiple entities on the signalling path. In addition, since the
server-recommended keep-alive frequency might vary between different
SIP entities, a single Flow-Timer header field can not be used to
indicate all the different frequency values.
6. Connection reuse
Keep-alives are often sent in order to keep NAT bindings open, so
that the NAT may be passed by SIP requests sent in the reverse
direction, reusing the same connection, or for non-connection-
oriented transport protocols, reusing the same path. This
specification does not define such connection reuse mechanism. The
keep-alive mechanism defined in this specification is only used to
negotiate the sending and receiving of keep-alives. Entities that
want to reuse connections need to use another mechanism to ensure
that security aspects associated with connection reuse are taken into
consideration.
RFC 5923 [RFC5923] specifies a mechanism for using connection-
oriented transports to send requests in the reverse direction, and an
entity that wants to use connection-reuse as well as indicate support
of keep-alives on that connection will insert both the "alias"
parameter defined in [RFC5923] as well as the "keep" parameter
defined in this specification.
SIP Outbound specifies how registration flows are used to send
requests in the reverse direction.
7. Examples
7.1. General
This section shows example flows where usage of keep-alives,
associated with a registration and a dialog, is negotiated between
different SIP entities.
NOTE: The examples do not show the actual syntactical encoding of the
request lines, response lines and the Via header fields, but rather a
pseudo code in order to identity the message type and to which SIP
entity a Via header field is associated.
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7.2. Keep-alive negotiation associated with registration: UA-proxy
Figure 1 shows an example where Alice sends an REGISTER request. She
indicates willingness of sending keep-alive by inserting a "keep"
parameter in her Via header field of the request. The edge proxy
(P1) forwards the request towards the registrar.
P1 is willing to receive keep-alives from Alice for the duration of
the registration, so when P1 receives the associated response it adds
a "keep" parameter value, which indicates a recommended keep-alive
frequency of 30 seconds, to Alice's Via header field, before it
forwards the response towards Alice.
When Alice receives the response, she determines from her Via header
field that P1 is willing to receive keep-alives associated with the
registration. Until the registration expires, or Alice sends a
registration refresh request, Alice then sends periodic keep-alives
(in this example using the STUN keep-alive technique) towards P1,
using the recommended keep-alive frequency indicated by the "keep"
parameter value.
Alice P1 REGISTRAR
| | |
|--- REGISTER------------->| |
| Via: Alice;keep | |
| |--- REGISTER-------------->|
| | Via: P1 |
| | Via: Alice;keep |
| | |
| |<-- 200 OK ----------------|
| | Via: P1 |
| | Via: Alice;keep |
|<-- 200 OK ---------------| |
| Via: Alice;keep=30 | |
| | |
| | |
| *** Timeout *** |
| | |
|=== STUN request ========>| |
|<== STUN response ========| |
| | |
| *** Timeout *** |
| | |
|=== STUN request ========>| |
|<== STUN response ========| |
| | |
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Figure 1: Example call flow
7.3. Keep-alive negotiation associated with dialog: UA-proxy
Figure 2 shows an example where Alice sends an initial INVITE request
for a dialog. She indicates willingness to send keep-alive by
inserting a "keep" parameter in her Via header field of the request.
The edge proxy (P1) adds itself to the dialog route set by adding
itself to a Record-Route header field, before it forwards the request
towards Bob.
P1 is willing to receive keep-alives from Alice for the duration of
the dialog, so When P1 receives the associated response it adds a
"keep" parameter value, which indicates a recommended keep-alive
frequency of 30 seconds, to Alice's Via header field, before it
forwards the response towards Alice.
When Alice receives the response, she determines from her Via header
field that P1 is willing to receive keep-alives associated with the
dialog. For the lifetime of the dialog, Alice then sends periodic
keep-alives (in this example using the STUN keep-alive technique)
towards P1, using the recommended keep-alive frequency indicated by
the "keep" parameter value.
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Alice P1 Bob
| | |
|--- INVITE -------------->| |
| Via: Alice;keep | |
| |--- INVITE --------------->|
| | Via: P1 |
| | Via: Alice;keep |
| | Record-Route: P1 |
| | |
| |<-- 200 OK ----------------|
| | Via: P1 |
| | Via: Alice;keep |
| | Record-Route: P1 |
|<-- 200 OK ---------------| |
| Alice: UAC;keep=30 | |
| Record-Route: P1 | |
| | |
|--- ACK ----------------->| |
| | |
| |--- ACK ------------------>|
| | |
| *** Timeout *** |
| | |
|=== STUN request ========>| |
|<== STUN response ========| |
| | |
| *** Timeout *** |
| | |
|=== STUN request ========>| |
|<== STUN response ========| |
| | |
| | |
|--- BYE ----------------->| |
| | |
| |--- BYE ------------------>|
| | |
| |<-- 200 OK ----------------|
| | |
Figure 2: Example call flow
7.4. Keep-alive negotiation associated with dialog: UA-UA
Figure 3 shows an example where Alice sends an initial INVITE request
for a dialog. She indicates willingness to send keep-alive by
inserting a "keep" parameter in her Via header field of the request.
The edge proxy (P1) does not add itself to the dialog route set, by
adding itself to a Record-Route header field, before it forwards the
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request towards Bob.
When Alice receives the response, she determines from her Via header
field that P1 is not willing to receive keep-alives associated with
the dialog from her. When the dialog route set has been established,
Alice sends a mid-dialog UPDATE request towards Bob (since P1 did not
insert itself in the dialog route set), and she once again indicates
willingness to send keep-alives by inserting a "keep" parameter in
her Via header field of the request. Bob supports the keep-alive
mechanism, and is willing to receive keep-alives associated with the
dialog from Alice, so he creates a response and adds a "keep"
parameter value, which indicates a recommended keep-alive frequency
of 30 seconds, to Alice's Via header field, before he forwards the
response towards Alice.
When Alice receives the response, she determines from her Via header
field that P1 is willing to receive keep-alives associated with the
dialog. For the lifetime of the dialog, Alice then sends periodic
keep-alives (in this example using the STUN keep-alive technique)
towards Bob, using the recommended keep-alive frequency indicated by
the "keep" parameter value.
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Alice P1 Bob
| | |
|--- INVITE -------------->| |
| Via: Alice;keep | |
| |--- INVITE --------------->|
| | Via: P1 |
| | Via: Alice:keep |
| | |
| |<-- 200 OK ----------------|
| | Via: P1 |
| | Via: Alice;keep |
|<-- 200 OK ---------------| |
| Via: Alice;keep | |
| | |
| |
|--- ACK --------------------------------------------->|
| |
|--- UPDATE ------------------------------------------>|
| Via: Alice;keep |
| |
|<-- 200 OK ------------------------------------------>|
| Via: UAC;keep=30 |
| |
| |
| *** Timeout *** |
| |
|=== STUN request ====================================>|
|<== STUN response ====================================|
| |
| *** Timeout *** |
| |
|=== STUN request ====================================>|
|<== STUN response ====================================|
| |
| |
|--- BYE --------------------------------------------->|
| |
|<-- 200 OK -------------------------------------------|
| |
Figure 3: Example call flow
8. Grammar
This specification defines a new Via header field parameter, "keep".
The ABNF [RFC5234] is:
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via-params =/ keep
keep = "keep" [ EQUAL 1*(DIGIT) ]
9. IANA Considerations
9.1. keep
This specification defines a new Via header field parameter called
keep in the "Header Field Parameters and Parameter Values" sub-
registry as per the registry created by [RFC3968]. The syntax is
defined in Section 8. The required information is:
Predefined
Header Field Parameter Name Values Reference
---------------------- --------------------- ---------- ---------
Via keep No [RFCXXXX]
10. Security Considerations
SIP entities that send or receive keep-alives are often required to
use a connection reuse mechanism, in order to ensure that requests
sent in the reverse direction, towards the sender of the keep-alives,
traverse NATs etc. This specification does not specify a connection
reuse mechanism, and it does it address security issues related to
connection reuse. SIP entities that wish to reuse connections need
to use a dedicated connection reuse mechanism, in conjunction with
the keep-alive negotiation mechanism.
Unless SIP messages are integrity protected hop-by-hop (e.g. using
TLS or DTLS), a man-in-the-middle can modify Via header fields used
by two entities to negotiate sending of keep-alives, e.g. by removing
the indications used to indicate willingness to send and receive
keep-alives, or by decreasing the timer value to a very low value,
which might trigger additional resource consumption due to the
frequently sent keep-alives.
The behavior defined in Sections 4.3 and 4.4 require a SIP entity
using the mechanism defined in this specification to place a value in
the "keep" parameter in the topmost Via header field value of a
response the SIP entity sends. They do not instruct the enity to
place a value in a "keep" parameter of any request it forwards. In
particular, SIP proxies MUST NOT place a value into the keep
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parameter of the topmost Via header field value of a request it
receives before forwarding it. A SIP proxy implementing this
specification SHOULD remove any keep parameter values in any Via
header field values below the topmost one in responses it receives
before forwarding them.
When requests are forwarded across multiple hops, it is possible for
a malicious downstream SIP entity to tamper with the accrued values
in the Via header field. The malicious SIP entity could place a
value, or change an existing value in a "keep" parameter in any of
the Via header field values, not just the topmost value. A proxy
implementation that simply forwards responses by stripping the
topmost Via header field value and not inspecting the resulting new
topmost Via header field value risks being adversely affected by such
a malicious downstream SIP entity. In particular, such a proxy may
start receiving STUN requests if it blindly forwards a response with
a keep parameter with a value it did not create in the topmost Via
header field. To lower the chances of the malicious SIP entity's
actions having adverse affects on such proxies, when a SIP entity
sends STUN keep-alives to an adjacent downstream SIP entity and does
not receive a response to those STUN messages, it MUST stop sending
the keep-alive requests for the remaining duration of the dialog (if
the sending of keep-alives were negotiated for a dialog) or until the
sending of keep-alives is re-negotiated for the registration (if the
sending keep-alives were negotiated for a registration).
In order to prevent attacks, when a SIP entity sends STUN keep-alives
to an adjacent downstream SIP entity that is not willing to receive
keep-alives (or does not support STUN), but for which willingness to
receive keep-alives has been inidicated by some other downstream SIP
entity, if the sending SIP entity does not receive a response to any
of the STUN keep-alive requests, it MUST stop sending the keep-alive
requests for the remaining duration of the dialog (if the sending of
keep-alives were negotiated for a dialog) or until the sending of
keep-alives is re-negotiated for the registration (if the sending
keep-alives were negotiated for a registration). Further actions
taken by the sending SIP entity is outside the scope of this
specification.
Apart from the issues described above, this specification does not
introduce security considerations in addition to those specified for
keep-alives in [RFC5626].
11. Acknowledgements
Thanks to Staffan Blau, Francois Audet, Hadriel Kaplan, Sean Schneyer
and Milo Orsic for their comments on the initial draft. Thanks to
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Juha Heinaenen, Jiri Kuthan, Dean Willis, John Elwell, Paul Kyzivat,
Peter Musgrave, Dale Worley, Adam Roach and Robert Sparks for their
comments on the list. Thanks to Vijay Gurbani for providing text
about the relationship with the connect reuse specification.
12. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-sipcore-keep-08
o Changes based on AD review comments by Robert Sparks
o Additional security considerations text provided by Robert Sparks
o http://www.ietf.org/mail-archive/web/sipcore/current/msg03779.html
(Nov 23rd)
o http://www.ietf.org/mail-archive/web/sipcore/current/msg03780.html
(Nov 23rd)
Changes from draft-ietf-sipcore-keep-07
o Last paragraph of section 4.2.2 removed
o Reference correction
Changes from draft-ietf-sipcore-keep-06
o New text added to the security considerations
Changes from draft-ietf-sipcore-keep-05
o New section about connection reuse added
o Clarify that the specification does not define a mechanism for
connection reuse
o New text added to the security considerations
o CRLF changed to double-CRLF in some places
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
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[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client-
Initiated Connections in the Session Initiation Protocol
(SIP)", RFC 5626, October 2009.
13.2. Informative References
[RFC3968] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Header Field Parameter Registry for the Session
Initiation Protocol (SIP)", BCP 98, RFC 3968,
December 2004.
[RFC5923] Gurbani, V., Mahy, R., and B. Tate, "Connection Reuse in
the Session Initiation Protocol (SIP)", RFC 5923,
June 2010.
Author's Address
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
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