draft-ietf-straw-b2bua-stun-04.txt   draft-ietf-straw-b2bua-stun-05.txt 
STRAW R. Ravindranath STRAW Ram. Ravindranath
Internet-Draft T. Reddy Internet-Draft T. Reddy
Intended status: Standards Track G. Salgueiro Intended status: Standards Track G. Salgueiro
Expires: September 10, 2015 Cisco Expires: October 30, 2015 Cisco
March 9, 2015 April 28, 2015
Session Traversal Utilities for NAT (STUN) Message Handling for Session Session Traversal Utilities for NAT (STUN) Message Handling for Session
Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs) Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs)
draft-ietf-straw-b2bua-stun-04 draft-ietf-straw-b2bua-stun-05
Abstract Abstract
Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs) Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs)
are often designed to be on the media path, rather than just are often designed to be on the media path, rather than just
intercepting signaling. This means that B2BUAs often act on the intercepting signaling. This means that B2BUAs often act on the
media path leading to separate media legs that the B2BUA correlates media path leading to separate media legs that the B2BUA correlates
and bridges together. When acting on the media path, B2BUAs are and bridges together. When acting on the media path, B2BUAs are
likely to receive Session Traversal Utilities for NAT (STUN) packets likely to receive Session Traversal Utilities for NAT (STUN) packets
as part of Interactive Connectivity Establishment (ICE) processing. as part of Interactive Connectivity Establishment (ICE) processing.
It is critical that B2BUAs handle these STUN messages properly.
This document defines behavior for a B2BUA performing ICE processing. This document defines behavior for a B2BUA performing ICE processing.
The goal of this draft is to ensure that ICE used for NAT and The goal of this draft is to ensure that B2BUAs properly handle STUN
Firewall traversal of multimedia sessions works when there are B2BUAs messages received as part of the ICE procedures used for NAT and
in place and the B2BUAs handle STUN messages properly. Firewall traversal of multimedia sessions.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2015. This Internet-Draft will expire on October 30, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 27 skipping to change at page 2, line 22
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SDP-Modifying Signaling-only B2BUA . . . . . . . . . . . . . 5 3. SDP-Modifying Signaling-only B2BUA . . . . . . . . . . . . . 5
4. Media Plane B2BUAs . . . . . . . . . . . . . . . . . . . . . 5 4. Media Plane B2BUAs . . . . . . . . . . . . . . . . . . . . . 5
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. ICE Termination with B2BUA . . . . . . . . . . . . . . . 6 4.2. Mandatory ICE Termination with B2BUA . . . . . . . . . . 5
4.3. ICE Passthrough with B2BUAs . . . . . . . . . . . . . . . 8 4.3. Optional ICE Termination with B2BUA . . . . . . . . . . . 8
4.4. STUN Handling in B2BUA with Forked Signaling . . . . . . 11 4.4. STUN Handling in B2BUA with Forked Signaling . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
In many SIP deployments, SIP entities exist in the SIP signaling and In many Session Initiation Protocol (SIP) deployments, SIP entities
media path between the originating and final terminating endpoints, exist in the SIP signaling and media path between the originating and
which go beyond the definition of a traditional SIP proxy. These SIP final terminating endpoints, which go beyond the definition of a
entities, commonly known as Back-to-Back User Agents (B2BUAs), are traditional SIP proxy. These SIP entities, commonly known as Back-
described in [RFC7092] and often perform functions not defined in to-Back User Agents (B2BUAs), are described in [RFC7092] and often
Standards Track RFCs. perform functions not defined in Standards Track RFCs.
The Session Initiation Protocol (SIP) [RFC3261], and other session SIP [RFC3261], and other session control protocols that try to use
control protocols that try to use direct path for media, are direct path for media, are typically difficult to use across Network
typically difficult to use across Network Address Translators (NATs). Address Translators (NATs). These protocols use IP addresses and
These protocols use IP addresses and transport port numbers encoded transport port numbers encoded in the signaling, such as the Session
in the signaling, such as the Session Description Protocol (SDP) Description Protocol (SDP) [RFC4566] and, in the case of SIP, various
[RFC4566] and, in the case of SIP, various header fields. Such header fields. Such addresses and ports are unreachable if any peers
addresses and ports are unreachable unless all peers in a session are are separated by NATs.
located behind the same NAT.
Mechanisms such as Session Traversal Utilities for NAT (STUN) Mechanisms such as Session Traversal Utilities for NAT (STUN)
[RFC5389], Traversal Using Relays around NAT (TURN) [RFC5766], and [RFC5389], Traversal Using Relays around NAT (TURN) [RFC5766], and
Interactive Connectivity Establishment (ICE) [RFC5245] did not exist Interactive Connectivity Establishment (ICE) [RFC5245] did not exist
when protocols like SIP began being deployed. Some mechanisms, such when protocols like SIP began being deployed. Some mechanisms, such
as the early versions of STUN, started appearing but they were as the early versions of STUN, started appearing but they were
unreliable and suffered a number of issues typical for UNilateral unreliable and suffered a number of issues typical for UNilateral
Self-Address Fixing (UNSAF) and described in [RFC3424]. For these Self-Address Fixing (UNSAF) and described in [RFC3424]. For these
and other reasons, Session Border Controllers (SBCs) that were and other reasons, B2BUAs were already being used by SIP domains for
already being used by SIP domains for other SIP and media-related other SIP and media-related purposes began to use proprietary
purposes began to use proprietary mechanisms to enable SIP devices mechanisms to enable SIP devices behind NATs to communicate across
behind NATs to communicate across the NAT. [RFC7362] describes how the NAT.
B2BUAs can perform Hosted NAT Traversal (HNT) in certain deployments.
Section 5 of [RFC7362] describes some of the issues with SBCs [RFC7362] describes how B2BUAs can perform Hosted NAT Traversal (HNT)
implementing HNT and offers some mitigation strategies. The most in certain deployments. Section 5 of [RFC7362] describes some of the
commonly used approach to solve these issues is "restricted- issues with SBCs implementing HNT and offers some mitigation
latching", whereby the B2BUA will not latch to any packets from a strategies. The most commonly used approach to solve these issues is
source public IP address other than the one the SIP UA uses for SIP "restricted-latching", whereby the B2BUA will not latch to any
signaling. However, this is susceptible to attacks, where an packets from a source public IP address other than the one the SIP UA
attacker who is able to see the source IP address of the SIP UA may uses for SIP signaling. However, this is susceptible to attacks,
generate packets using the same IP address. There are other threats where an attacker who is able to see the source IP address of the SIP
described in Section 5 of [RFC7362] for which Secure Real-time UA may generate packets using the same IP address. There are other
Transport Protocol (SRTP) [RFC3711] can be used as a solution. threats described in Section 5 of [RFC7362] for which Secure Real-
However, this would require the B2BUAs to be terminating/re- time Transport Protocol (SRTP) [RFC3711] can be used as a solution.
originating SRTP, which is not always desirable. A B2BUA can use ICE However, this would require the B2BUAs to terminate and re-originate
[RFC5245], which provides authentication tokens (conveyed in the ice- SRTP, which is not always desirable.
ufrag and ice-pwd attributes) that allow the identity of a peer to be
confirmed before engaging in media exchange. This can solve some of A B2BUA can use ICE [RFC5245], which provides authentication tokens
the security concerns with HNT solution. Further, ICE has other (conveyed in the ice-ufrag and ice-pwd attributes) that allow the
benefits like selecting an address when more than one address is identity of a peer to be confirmed before engaging in media exchange.
available (e.g., dual-stack environment where host can have both IPv4 This can solve some of the security concerns with HNT solution.
and IPv6 addresses), verifying that a path works before connecting Further, ICE has other benefits like selecting an address when more
the call etc. For these reasons endpoints often use ICE to pick a than one address is available (e.g., dual-stack environment where
candidate pair for media traffic between two agents. host can have both IPv4 and IPv6 addresses), verifying that a path
works before connecting the call etc. For these reasons endpoints
often use ICE to pick a candidate pair for media traffic between two
agents.
B2BUAs often operate on the media path and have the ability to modify B2BUAs often operate on the media path and have the ability to modify
SIP headers and SDP bodies as part of their normal operation. Such SIP headers and SDP bodies as part of their normal operation. Such
entities, when present on the media path, are likely to take an entities, when present on the media path, are likely to take an
active role in the session signaling depending on their level of active role in the session signaling depending on their level of
activity on the media path. For example, some B2BUAs modify portions activity on the media path. For example, some B2BUAs modify portions
of the SDP body (e.g., IP address, port) and subsequently modify the of the SDP body (e.g., IP address, port) and subsequently modify the
media packet headers as well. Section 18.6 of ICE [RFC5245] explains media packet headers as well. Section 18.6 of ICE [RFC5245] explains
two different behaviors when B2BUAs are present. Some B2BUAs are two different behaviors when B2BUAs are present. Some B2BUAs are
likely to remove all the SDP ICE attributes before sending the SDP likely to remove all the SDP ICE attributes before sending the SDP
across to the other side. Consequently, the call will appear to both across to the other side. Consequently, the call will appear to both
endpoints as though the other side doesn't support ICE. There are endpoints as though the other side doesn't support ICE. There are
other types of B2BUAs that pass the ICE attributes without other types of B2BUAs that pass the ICE attributes without
modification, yet modify the default destination for media contained modification, yet modify the default destination for media contained
in the m= and c= lines and rtcp attribute (defined in [RFC3605]). in the m= and c= lines and rtcp attribute (defined in [RFC3605]).
This will be detected as an ICE mismatch and ICE processing is
aborted for the call. The call may continue if the endpoints are This will be detected as an ICE mismatch and ICE processing will be
able to reach each other over the default candidate (sent in m= and aborted for the session. The session may continue if the endpoints
c= lines). are able to reach each other over the default candidate (sent in m=
and c= lines).
Section 3.1.3 of [RFC7092] defines a SDP-Modifying Signaling-only Section 3.1.3 of [RFC7092] defines a SDP-Modifying Signaling-only
B2BUA that operates in the signaling plane only and is not in the B2BUA that operates in the signaling plane only and is not in the
media path, but it does modify SDP bodies and is thus aware of and media path, but it does modify SDP bodies and is thus aware of and
understands SDP syntax and semantics. Such B2BUA MUST follow the understands SDP syntax and semantics. Such B2BUA MUST follow the
behavior mentioned in Section 3 of this specification. behavior mentioned in Section 3.
Section 3.2 of [RFC7092] describes three different categories of Section 3.2 of [RFC7092] describes three different categories of
B2BUAs that operates on both signaling(SIP and SDP) and media plane B2BUAs that operates on both signaling(SIP and SDP) and media plane
according to the level of involvement and active participation in the according to the level of involvement and active participation in the
media plane: media plane:
o A B2BUA that acts as a simple media relay effectively unaware of o A B2BUA that acts as a simple media relay effectively unaware of
anything that is transported and only modifies the transport anything that is transported and only modifies the transport
header (could be UDP/IP) of the media packets. header (could be UDP/IP) of the media packets.
o A B2BUA that performs a media-aware role. It inspects and o A B2BUA that performs a media-aware role. It inspects and
potentially modifies RTP or RTP Control Protocol (RTCP) headers; potentially modifies RTP or RTP Control Protocol (RTCP) headers;
but it does not modify the payload of RTP/RTCP. but it does not modify the payload of RTP/RTCP.
o A B2BUA that performs a media-termination role and operates at the o A B2BUA that performs a media-termination role and operates at the
media payload layer, such as RTP/RTCP payload (e.g., a media payload layer, such as RTP/RTCP payload (e.g., a
transcoder). transcoder).
When such a B2BUA operating on a media plane is involved in a call When such a B2BUA operating on a media plane is involved in a session
between two endpoints performing ICE, then it MUST follow the between two endpoints performing ICE, then it MUST follow the
behavior described in section 4 of this specification. behavior described in Section 4.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The following generalized terms are defined in [RFC3261], Section 6.
B2BUA: A SIP Back-to-Back User Agent, which is the logical
combination of a User Agent Server (UAS) and User Agent Client
(UAC).
UAS: A SIP User Agent Server.
UAC: A SIP User Agent Client.
All of the pertinent B2BUA terminology and taxonomy used in this All of the pertinent B2BUA terminology and taxonomy used in this
document is based on [RFC7092]. document is defined in [RFC7092].
Network Address Translators (NATs) are widely used in the Internet by Network Address Translators (NATs) are widely used in the Internet by
consumers and organizations. Although specific NAT behaviors vary, consumers and organizations. Although specific NAT behaviors vary,
this document uses the term "NAT", which maps to NAT and NAPT terms this document uses the term "NAT", which maps to NAT and NAPT terms
from [RFC3022], for devices that map any IPv4 or IPv6 address and from [RFC3022], for devices that map any IPv4 or IPv6 address and
transport port number to another IPv4 or IPv6 address and transport transport port number to another IPv4 or IPv6 address and transport
port number. This includes consumer NATs, Firewall-NATs, IPv4-IPv6 port number. This includes consumer NATs, Firewall-NATs, IPv4-IPv6
NATs, Carrier-Grade NATs (CGNs) [RFC6888], etc. NATs, Carrier-Grade NATs (CGNs) [RFC6888], etc.
3. SDP-Modifying Signaling-only B2BUA 3. SDP-Modifying Signaling-only B2BUA
An SDP-Modifying Signaling-only B2BUA is one that operates in the An SDP-Modifying Signaling-only B2BUA is one that operates in the
signaling plane only and is not in the media path, but it modifies signaling plane only and is not in the media path, but it modifies
SDP bodies as described in section 3.1.3 of [RFC7092]. Such B2BUAs SDP bodies as described in section 3.1.3 of [RFC7092]. Such B2BUAs
MUST ensure that they don't change IP address in c= line, port in m= MUST NOT change IP address in c= line, port in m= line and ICE
line and ICE semantics of SDP as doing so can cause ICE-mismatch. semantics of SDP as doing so can cause ICE-mismatch.
4. Media Plane B2BUAs 4. Media Plane B2BUAs
4.1. Overview 4.1. Overview
When one or both of the endpoints are behind a NAT, and there is a When one or both of the endpoints are behind a NAT, and there is a
B2BUA between the endpoints, the B2BUAs MUST support ICE or at a B2BUA between the endpoints, the B2BUAs MUST support ICE or at a
minimum support ICE LITE functionality as described in [RFC5245]. minimum support ICE LITE functionality as described in [RFC5245].
Such B2BUAs MUST use the mechanism described in Section 2.2 of Such B2BUAs MUST use the mechanism described in Section 2.2 of
[RFC5245] to demultiplex STUN packets that arrive on the Real-time [RFC5245] to demultiplex STUN packets that arrive on the Real-time
Transport Protocol(RTP)/RTP Control Protocol (RTCP) port. Transport Protocol(RTP)/RTP Control Protocol (RTCP) port.
The subsequent sections describe the behavior B2BUA's MUST follow for The subsequent sections describe the behavior B2BUA's MUST follow for
handling ICE messages. A B2BUA can terminate ICE and thus have two handling ICE messages. A B2BUA can terminate ICE and thus have two
ICE contexts with either endpoint. The reason for ICE termination ICE contexts with either endpoint. The reason for ICE termination
could be due to the need for B2BUA to be in the media path ( e.g., could be due to the need for B2BUA to be in the media path ( e.g.,
address hiding for privacy, interworking between ICE to no-ICE, address hiding for privacy, interworking between ICE to no-ICE,
etc.). A B2BUA can also be in ICE passthrough mode and passes across etc.). A B2BUA can also be in optional ICE termination mode and
the candidate list and STUN short-term credentials (ice-ufrag and passes across the candidate list and STUN short-term credentials
ice-pwd attributes from one endpoint to the other side. A B2BUA may (ice-ufrag and ice-pwd attributes from one endpoint to the other side
be in ICE passthrough mode when it does not have a need to be on the after adding its own candidates. A B2BUA may be in optional ICE
media path. The below sections describes the behaviors for these two termination mode when it does not have a need to be on the media
path. The below sections describes the behaviors for these two
cases. cases.
4.2. ICE Termination with B2BUA 4.2. Mandatory ICE Termination with B2BUA
A B2BUA that wishes to be in the media path follows the below steps: A B2BUA that wishes to always be in the media path follows the below
steps:
o When a B2BUA sends out SDP, it MUST advertise support for ICE and o When a B2BUA sends out SDP, it MUST advertise support for ICE and
MAY include B2BUA candidates of different types for each component MAY include B2BUA candidates of different types for each component
of each media stream. of each media stream.
o If the B2BUA is in ICE lite mode as described in Section 2.7 of o If the B2BUA is in ICE lite mode as described in Section 2.7 of
[RFC5245] then it MUST send a=ice-lite attribute and MUST include [RFC5245] then it MUST send a=ice-lite attribute and MUST include
B2BUAs host candidates for each component of each media stream. B2BUAs host candidates for each component of each media stream.
o If the B2BUA supports full ICE then it MAY include B2BUAs o If the B2BUA supports full ICE then it MAY include B2BUAs
skipping to change at page 7, line 46 skipping to change at page 7, line 46
| (9) | checks +conclusion | | (9) | checks +conclusion |
| | (10) | | | (10) |
|<-------Media packets -->|<----Media packets-------->| |<-------Media packets -->|<----Media packets-------->|
| (13) | (14) | | (13) | (14) |
| | | | | |
|<---ICE keepalives 1---->| | |<---ICE keepalives 1---->| |
| (15) |<----ICE keep alives 2---->| | (15) |<----ICE keep alives 2---->|
(16) (16)
Figure 1: INVITE with SDP having ICE and with a Media Plane B2BUA Figure 1: INVITE with SDP having ICE and with a Media Plane B2BUA
terminating ICE
The above figure shows an example call flow with two endpoints Alice The above figure shows an example call flow with two endpoints Alice
and Bob doing ICE and a B2BUA handing STUN messages from both the and Bob doing ICE and a B2BUA handing STUN messages from both the
endpoints. For the sake of brevity the entire ICE SDP attributes are endpoints. For the sake of brevity the entire ICE SDP attributes are
not shown. Also the STUN messages exchanged as part of ICE not shown. Also the STUN messages exchanged as part of ICE
connectivity checks are not shown. Key steps to note from the call connectivity checks are not shown. Key steps to note from the call
flow are: flow are:
o Alice sends an INVITE with SDP having ICE candidates. o Alice sends an INVITE with SDP having ICE candidates.
skipping to change at page 8, line 40 skipping to change at page 8, line 42
and between Bob and B2BUA (step 16) to keep NAT and Firewall and between Bob and B2BUA (step 16) to keep NAT and Firewall
bindings alive. bindings alive.
Since there are two independent ICE contexts on either side of the Since there are two independent ICE contexts on either side of the
B2BUA it is possible that ICE checks will conclude on one side before B2BUA it is possible that ICE checks will conclude on one side before
concluding on the other side. This could result in an ongoing media concluding on the other side. This could result in an ongoing media
session for one end, while the other is still being set up. Any such session for one end, while the other is still being set up. Any such
media received by the B2BUA would continue to be sent to the other media received by the B2BUA would continue to be sent to the other
side on the default candidate address (that was sent in c= line). side on the default candidate address (that was sent in c= line).
4.3. ICE Passthrough with B2BUAs 4.3. Optional ICE Termination with B2BUA
If a B2BUA does not see a need to be in the media path, it can do the If a B2BUA is willing to be in the media path if needed for NAT
following steps mentioned in this section. traversal, but does not otherwise require it can do the following
steps mentioned in this section.
o When a B2BUA receives an incoming SDP with ICE semantics it copies o When a B2BUA receives an incoming SDP with ICE semantics it copies
the received candidate list and appends its own candidate list in the received candidate list and appends its own candidate list in
the outgoing SDP. The B2BUA also copies the ufrag/password values the outgoing SDP. The B2BUA also copies the ufrag/password values
it received in the incoming SDP to the outgoing SDP and then sends it received in the incoming SDP to the outgoing SDP and then sends
out the SDP. out the SDP.
o The B2BUAs candidates MAY have lower-priority than the candidates o The B2BUAs candidates MAY have lower-priority than the candidates
provided by the endpoint, this way endpoint and remote peer provided by the endpoint, this way endpoint and remote peer
candidate pairs are tested first before trying candidate pairs candidate pairs are tested first before trying candidate pairs
with B2BUA candidates. with B2BUA candidates.
o After offer/answer is complete, the endpoints will have both the o After offer/answer is complete, the endpoints will have both the
B2BUA's and remote peer candidates. It will then use ICE B2BUA's and remote peer candidates. It will then use ICE
procedures described in [RFC5245] to nominate a candidate pair for procedures described in Section 8 of [RFC5245] to nominate a
sending and receiving media streams. candidate pair for sending and receiving media streams.
o With this approach the B2BUA will be in the media path only if the o With this approach the B2BUA will be in the media path only if the
ICE checks between all the candidate pairs formed from both the ICE checks between all the candidate pairs formed from both the
endpoints fail. endpoints fail.
+-------+ +------------------+ +-----+ +-------+ +------------------+ +-----+
| Alice | | Mediaplane B2BUA | | Bob | | Alice | | Mediaplane B2BUA | | Bob |
+-------+ +------------------+ +-----+ +-------+ +------------------+ +-----+
|(1) INVITE | (3)INVITE | |(1) INVITE | (3)INVITE |
| a=ice-ufrag1 | a=ice-ufrag1 | | a=ice-ufrag1 | a=ice-ufrag1 |
skipping to change at page 10, line 49 skipping to change at page 10, line 49
| checks+conclusion |<-----ICE Connectivity 2-->| | checks+conclusion |<-----ICE Connectivity 2-->|
| (10) | checks +conclusion | | (10) | checks +conclusion |
| | (11) | | | (11) |
|<-------------------Media packets------------------->| |<-------------------Media packets------------------->|
| (12) | | (12) |
| | | | | |
|<------------------ICE keepalives------------------->| |<------------------ICE keepalives------------------->|
(13) (13)
Figure 2: INVITE with SDP having ICE and with a Media Plane B2BUA in Figure 2: INVITE with SDP having ICE and with a Media Plane B2BUA in
ICE Passthrough mode optional ICE termination mode
The above figure shows a sample call flow with two endpoints Alice The above figure shows a sample call flow with two endpoints Alice
and Bob doing ICE and a B2BUA handing STUN messages from both the and Bob doing ICE and a B2BUA handing STUN messages from both the
endpoints. For the sake of brevity the entire ICE SDP attributes are endpoints. For the sake of brevity the entire ICE SDP attributes are
not shown. Also the STUN messages exchanged as part of ICE not shown. Also the STUN messages exchanged as part of ICE
connectivity checks are not shown. Key steps to note from the call connectivity checks are not shown. Key steps to note from the call
flow are: flow are:
o Alice sends an INVITE with an SDP having its own candidate list. o Alice sends an INVITE with an SDP having its own candidate list.
skipping to change at page 12, line 7 skipping to change at page 12, line 7
ICE as described in Section 2.5 of [RFC5245] uses STUN short-term ICE as described in Section 2.5 of [RFC5245] uses STUN short-term
credential mechanism for authentication and message integrity. STUN credential mechanism for authentication and message integrity. STUN
connectivity checks include MESSAGE-INTEGRITY attribute that contains connectivity checks include MESSAGE-INTEGRITY attribute that contains
HMAC-SHA1 of the STUN message and the HMAC is computed using the key HMAC-SHA1 of the STUN message and the HMAC is computed using the key
exchanged in the signaling channel. The signaling channel between exchanged in the signaling channel. The signaling channel between
the endpoints and B2BUA MUST be encrypted so that the key is not the endpoints and B2BUA MUST be encrypted so that the key is not
visible to eavesdropper otherwise the security benefits of short-term visible to eavesdropper otherwise the security benefits of short-term
authentication would be lost. authentication would be lost.
The recommendations mentioned in Appendix of [RFC5245] for ICE and
Lite Agents also apply to a B2BUA doing ICE.
B2BUA when handling secure traffic (SRTP/SRTCP) SHOULD follow the
procedures mentioned in [I-D.ram-straw-b2bua-dtls-srtp] to ensure
that Man-in-the-Middle attacks are not possible.
6. IANA Considerations 6. IANA Considerations
This document makes no request of IANA. This document makes no request of IANA.
7. Acknowledgments 7. Acknowledgments
Special thanks to Dan Wing, Pal Martinsen, Charles Eckel, Marc Petit- Special thanks to Dan Wing, Pal Martinsen, Charles Eckel, Marc Petit-
Huguenin, Simon Perreault, Lorenzo Miniero, Ari Keranen and Huguenin, Simon Perreault, Lorenzo Miniero, Ari Keranen and
Parthasarathi R for their constructive comments, suggestions, and Parthasarathi R for their constructive comments, suggestions, and
early reviews that were critical to the formulation and refinement of early reviews that were critical to the formulation and refinement of
skipping to change at page 13, line 5 skipping to change at page 12, line 43
2010. 2010.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389, "Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008. October 2008.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.
8.2. Informative References [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents", RFC
7092, December 2013.
[I-D.ram-straw-b2bua-dtls-srtp] 8.2. Informative References
R, R., Reddy, T., Salgueiro, G., Pascual, V., and P.
Ravindran, "DTLS-SRTP Handling in Session Initiation
Protocol (SIP) Back-to-Back User Agents (B2BUAs)", draft-
ram-straw-b2bua-dtls-srtp-03 (work in progress), March
2015.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January Address Translator (Traditional NAT)", RFC 3022, January
2001. 2001.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
skipping to change at page 13, line 38 skipping to change at page 13, line 25
in Session Description Protocol (SDP)", RFC 3605, October in Session Description Protocol (SDP)", RFC 3605, October
2003. 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A., [RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Requirements for Carrier-Grade NATs and H. Ashida, "Common Requirements for Carrier-Grade NATs
(CGNs)", BCP 127, RFC 6888, April 2013. (CGNs)", BCP 127, RFC 6888, April 2013.
[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents", RFC
7092, December 2013.
[RFC7362] Ivov, E., Kaplan, H., and D. Wing, "Latching: Hosted NAT [RFC7362] Ivov, E., Kaplan, H., and D. Wing, "Latching: Hosted NAT
Traversal (HNT) for Media in Real-Time Communication", RFC Traversal (HNT) for Media in Real-Time Communication", RFC
7362, September 2014. 7362, September 2014.
Authors' Addresses Authors' Addresses
Ram Mohan Ravindranath Ram Mohan Ravindranath
Cisco Cisco
Cessna Business Park Cessna Business Park
Sarjapur-Marathahalli Outer Ring Road Sarjapur-Marathahalli Outer Ring Road
Bangalore, Karnataka 560103 Bangalore, Karnataka 560103
India India
Email: rmohanr@cisco.com Email: rmohanr@cisco.com
Tirumaleswar Reddy Tirumaleswar Reddy
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