17. Operational Considerations This section discusses issues relevant to operators operating networks where ICE will be used by endpoints. 17.1. NAT and Firewall Types ICE was designed to work with existing NAT and firewall equipment. Consequently, it is not necessary to replace or reconfigure existing firewall and NAT equipment in order to facilitate deployment of ICE. Indeed, ICE was developed to be deployed in environments where the Voice over IP (VoIP) operator has no control over the IP network infrastructure, including firewalls and NATs. That said, ICE works best in environments where the NAT devices are "behave" compliant, meeting the recommendations defined in [RFC4787] and [RFC5382]. In networks with behave-compliant NAT, ICE will work without the need for a TURN server, thus improving voice quality, decreasing call setup times, and reducing the bandwidth demands on the network operator. 17.2. Bandwidth Requirements Deployment of ICE can have several interactions with available network capacity that operators need to take into consideration. 17.2.1. STUN and TURN Server-Capacity Planning First and foremost, ICE makes use of TURN and STUN servers, which would typically be located in data centers. The STUN servers require relatively little bandwidth. For each component of each data stream, there will be one or more STUN transactions from each client to the STUN server. In a basic voice-only IPv4 VoIP deployment, there will be four transactions per call (one for RTP and one for RTCP, for both the caller and callee). Each transaction is a single request and a single response, the former being 20 bytes long, and the latter, 28.
Consequently, if a system has N users, and each makes four calls in a busy hour, this would require N*1.7bps. For one million users, this is 1.7 Mbps, a very small number (relatively speaking). TURN traffic is more substantial. The TURN server will see traffic volume equal to the STUN volume (indeed, if TURN servers are deployed, there is no need for a separate STUN server), in addition to the traffic for the actual data. The amount of calls requiring TURN for data relay is highly dependent on network topologies, and can and will vary over time. In a network with 100% behave-compliant NATs, it is exactly zero. The planning considerations above become more significant in multimedia scenarios (e.g., audio and video conferences) and when the numbers of participants in a session grow. 17.2.2. Gathering and Connectivity Checks The process of gathering candidates and performing connectivity checks can be bandwidth intensive. ICE has been designed to pace both of these processes. The gathering and connectivity-check phases are meant to generate traffic at roughly the same bandwidth as the data traffic itself will consume once the ICE process concludes. This was done to ensure that if a network is designed to support communication traffic of a certain type (voice, video, or just text), it will have sufficient capacity to support the ICE checks for that data. Once ICE has concluded, the subsequent ICE keepalives will later cause a marginal increase in the total bandwidth utilization; however, this will typically be an extremely small increase. Congestion due to the gathering and check phases has proven to be a problem in deployments that did not utilize pacing. Typically, access links became congested as the endpoints flooded the network with checks as fast as they could send them. Consequently, network operators need to ensure that their ICE implementations support the pacing feature. Though this pacing does increase call setup times, it makes ICE network friendly and easier to deploy. 17.2.3. Keepalives STUN keepalives (in the form of STUN Binding Indications) are sent in the middle of a data session. However, they are sent only in the absence of actual data traffic. In deployments with continuous media and without utilizing Voice Activity Detection (VAD), or deployments where VAD is utilized together with short interval (max 1 second) comfort noise, the keepalives are never used and there is no increase in bandwidth usage. When VAD is being used without comfort noise, keepalives will be sent during silence periods. This involves a
single packet every 15-20 seconds, far less than the packet every 20-30 ms that is sent when there is voice. Therefore, keepalives do not have any real impact on capacity planning. 17.3. ICE and ICE-Lite Deployments utilizing a mix of ICE and ICE-lite interoperate with each other. They have been explicitly designed to do so. However, ICE-lite can only be deployed in limited use cases. Those cases, and the caveats involved in doing so, are documented in Appendix A. 17.4. Troubleshooting and Performance Management ICE utilizes end-to-end connectivity checks and places much of the processing in the endpoints. This introduces a challenge to the network operator -- how can they troubleshoot ICE deployments? How can they know how ICE is performing? ICE has built-in features to help deal with these problems. Signaling servers, typically deployed in data centers of the network operator, will see the contents of the candidate exchanges that convey the ICE parameters. These parameters include the type of each candidate (host, server reflexive, or relayed), along with their related addresses. Once ICE processing has completed, an updated candidate exchange takes place, signaling the selected address (and its type). This updated signaling is performed exactly for the purposes of educating network equipment (such as a diagnostic tool attached to a signaling) about the results of ICE processing. As a consequence, through the logs generated by a signaling server, a network operator can observe what types of candidates are being used for each call and what addresses were selected by ICE. This is the primary information that helps evaluate how ICE is performing. 17.5. Endpoint Configuration ICE relies on several pieces of data being configured into the endpoints. This configuration data includes timers, credentials for TURN servers, and hostnames for STUN and TURN servers. ICE itself does not provide a mechanism for this configuration. Instead, it is assumed that this information is attached to whatever mechanism is used to configure all of the other parameters in the endpoint. For SIP phones, standard solutions such as the configuration framework [RFC6080] have been defined.
18. IAB Considerations The IAB has studied the problem of "Unilateral Self-Address Fixing" (UNSAF), which is the general process by which an ICE agent attempts to determine its address in another realm on the other side of a NAT through a collaborative protocol reflection mechanism [RFC3424]. ICE is an example of a protocol that performs this type of function. Interestingly, the process for ICE is not unilateral, but bilateral, and the difference has a significant impact on the issues raised by the IAB. Indeed, ICE can be considered a Bilateral Self-Address Fixing (B-SAF) protocol, rather than an UNSAF protocol. Regardless, the IAB has mandated that any protocols developed for this purpose document a specific set of considerations. This section meets those requirements. 18.1. Problem Definition From RFC 3424, any UNSAF proposal needs to provide: Precise definition of a specific, limited-scope problem that is to be solved with the UNSAF proposal. A short term fix should not be generalized to solve other problems. Such generalizations lead to the the prolonged dependence on and usage of the supposed short term fix -- meaning that it is no longer accurate to call it "short term". The specific problems being solved by ICE are: Providing a means for two peers to determine the set of transport addresses that can be used for communication. Providing a means for an agent to determine an address that is reachable by another peer with which it wishes to communicate. 18.2. Exit Strategy From RFC 3424, any UNSAF proposal needs to provide: Description of an exit strategy/transition plan. The better short term fixes are the ones that will naturally see less and less use as the appropriate technology is deployed. ICE itself doesn't easily get phased out. However, it is useful even in a globally connected Internet, to serve as a means for detecting whether a router failure has temporarily disrupted connectivity, for example. ICE also helps prevent certain security attacks that have nothing to do with NAT. However, what ICE does is help phase out other UNSAF mechanisms. ICE effectively picks amongst those
mechanisms, prioritizing ones that are better and deprioritizing ones that are worse. As NATs begin to dissipate as IPv6 is introduced, server-reflexive and relayed candidates (both forms of UNSAF addresses) simply never get used, because higher-priority connectivity exists to the native host candidates. Therefore, the servers get used less and less and can eventually be removed when their usage goes to zero. Indeed, ICE can assist in the transition from IPv4 to IPv6. It can be used to determine whether to use IPv6 or IPv4 when two dual-stack hosts communicate with SIP (IPv6 gets used). It can also allow a network with both 6to4 and native v6 connectivity to determine which address to use when communicating with a peer. 18.3. Brittleness Introduced by ICE From RFC 3424, any UNSAF proposal needs to provide: Discussion of specific issues that may render systems more "brittle". For example, approaches that involve using data at multiple network layers create more dependencies, increase debugging challenges, and make it harder to transition. ICE actually removes brittleness from existing UNSAF mechanisms. In particular, classic STUN (as described in RFC 3489 [RFC3489]) has several points of brittleness. One of them is the discovery process that requires an ICE agent to try to classify the type of NAT it is behind. This process is error prone. With ICE, that discovery process is simply not used. Rather than unilaterally assessing the validity of the address, its validity is dynamically determined by measuring connectivity to a peer. The process of determining connectivity is very robust. Another point of brittleness in classic STUN and any other unilateral mechanism is its absolute reliance on an additional server. ICE makes use of a server for allocating unilateral addresses, but it allows agents to directly connect if possible. Therefore, in some cases, the failure of a STUN server would still allow for a call to progress when ICE is used. Another point of brittleness in classic STUN is that it assumes the STUN server is on the public Internet. Interestingly, with ICE, that is not necessary. There can be a multitude of STUN servers in a variety of address realms. ICE will discover the one that has provided a usable address.
The most troubling point of brittleness in classic STUN is that it doesn't work in all network topologies. In cases where there is a shared NAT between each agent and the STUN server, traditional STUN may not work. With ICE, that restriction is removed. Classic STUN also introduces some security considerations. Fortunately, those security considerations are also mitigated by ICE. Consequently, ICE serves to repair the brittleness introduced in classic STUN, and it does not introduce any additional brittleness into the system. The penalty of these improvements is that ICE increases session establishment times. 18.4. Requirements for a Long-Term Solution From RFC 3424, any UNSAF proposal needs to provide the following: Identify requirements for longer term, sound technical solutions; contribute to the process of finding the right longer term solution. Our conclusions from RFC 3489 remain unchanged. However, we feel ICE actually helps because we believe it can be part of the long-term solution. 18.5. Issues with Existing NAPT Boxes From RFC 3424, any UNSAF proposal needs to provide: Discussion of the impact of the noted practical issues with existing, deployed NA[P]Ts and experience reports. A number of NAT boxes are now being deployed into the market that try to provide "generic" ALG functionality. These generic ALGs hunt for IP addresses, in either text or binary form within a packet, and rewrite them if they match a binding. This interferes with classic STUN. However, the update to STUN [RFC5389] uses an encoding that hides these binary addresses from generic ALGs. Existing NAPT boxes have non-deterministic and typically short expiration times for UDP-based bindings. This requires implementations to send periodic keepalives to maintain those bindings. ICE uses a default of 15 s, which is a very conservative estimate. Eventually, over time, as NAT boxes become compliant to behave [RFC4787], this minimum keepalive will become deterministic
and well known, and the ICE timers can be adjusted. Having a way to discover and control the minimum keepalive interval would be far better still. 19. Security Considerations 19.1. IP Address Privacy The process of probing for candidates reveals the source addresses of the client and its peer to any on-network listening attacker, and the process of exchanging candidates reveals the addresses to any attacker that is able to see the negotiation. Some addresses, such as the server-reflexive addresses gathered through the local interface of VPN users, may be sensitive information. If these potential attacks cannot be mitigated, ICE usages can define mechanisms for controlling which addresses are revealed to the negotiation and/or probing process. Individual implementations may also have implementation-specific rules for controlling which addresses are revealed. For example, [WebRTC-IP-HANDLING] provides additional information about the privacy aspects of revealing IP addresses via ICE for WebRTC applications. ICE implementations where such issues can arise are RECOMMENDED to provide a programmatic or user interface that provides control over which network interfaces are used to generate candidates. Based on the types of candidates provided by the peer, and the results of the connectivity tests performed against those candidates, the peer might be able to determine characteristics of the local network, e.g., if different timings are apparent to the peer. Within the limit, the peer might be able to probe the local network. There are several types of attacks possible in an ICE system. The subsections consider these attacks and their countermeasures. 19.2. Attacks on Connectivity Checks An attacker might attempt to disrupt the STUN connectivity checks. Ultimately, all of these attacks fool an ICE agent into thinking something incorrect about the results of the connectivity checks. Depending on the type of attack, the attacker needs to have different capabilities. In some cases, the attacker needs to be on the path of the connectivity checks. In other cases, the attacker does not need to be on the path, as long as it is able to generate STUN connectivity checks. While attacks on connectivity checks are typically performed by network entities, if an attacker is able to control an endpoint, it might be able to trigger connectivity-check attacks. The possible false conclusions an attacker can try and cause are:
False Invalid: An attacker can fool a pair of agents into thinking a candidate pair is invalid, when it isn't. This can be used to cause an agent to prefer a different candidate (such as one injected by the attacker) or to disrupt a call by forcing all candidates to fail. False Valid: An attacker can fool a pair of agents into thinking a candidate pair is valid, when it isn't. This can cause an agent to proceed with a session but then not be able to receive any data. False Peer-Reflexive Candidate: An attacker can cause an agent to discover a new peer-reflexive candidate when it is not expected to. This can be used to redirect data streams to a DoS target or to the attacker, for eavesdropping or other purposes. False Valid on False Candidate: An attacker has already convinced an agent that there is a candidate with an address that does not actually route to that agent (e.g., by injecting a false peer- reflexive candidate or false server-reflexive candidate). The attacker then launches an attack that forces the agents to believe that this candidate is valid. If an attacker can cause a false peer-reflexive candidate or false valid on a false candidate, it can launch any of the attacks described in [RFC5389]. To force the false invalid result, the attacker has to wait for the connectivity check from one of the agents to be sent. When it is, the attacker needs to inject a fake response with an unrecoverable error response (such as a 400), or drop the response so that it never reaches the agent. However, since the candidate is, in fact, valid, the original request may reach the peer agent and result in a success response. The attacker needs to force this packet or its response to be dropped through a DoS attack, a Layer 2 network disruption, or another technique. If it doesn't do this, the success response will also reach the originator, alerting it to a possible attack. The ability for the attacker to generate a fake response is mitigated through the STUN short-term credential mechanism. In order for this response to be processed, the attacker needs the password. If the candidate exchange signaling is secured, the attacker will not have the password, and its response will be discarded. Spoofed ICMP Hard Errors (Type 3, codes 2-4) can also be used to create false invalid results. If an ICE agent implements a response to these ICMP errors, the attacker is capable of generating an ICMP message that is delivered to the agent sending the connectivity check. The validation of the ICMP error message by the agent is its
only defense. For Type 3 code=4, the outer IP header provides no validation, unless the connectivity check was sent with DF=0. For codes 2 or 3, which are originated by the host, the address is expected to be any of the remote agent's host, reflexive, or relay candidate IP addresses. The ICMP message includes the IP header and UDP header of the message triggering the error. These fields also need to be validated. The IP destination and UDP destination port need to match either the targeted candidate address and port or the candidate's base address. The source IP address and port can be any candidate for the same base address of the agent sending the connectivity check. Thus, any attacker having access to the exchange of the candidates will have the necessary information. Hence, the validation is a weak defense, and the sending of spoofed ICMP attacks is also possible for off-path attackers from a node in a network without source address validation. Forcing the fake valid result works in a similar way. The attacker needs to wait for the Binding request from each agent and inject a fake success response. Again, due to the STUN short-term credential mechanism, in order for the attacker to inject a valid success response, the attacker needs the password. Alternatively, the attacker can route (e.g., using a tunneling mechanism) a valid success response, which normally would be dropped or rejected by the network, to the agent. Forcing the false peer-reflexive candidate result can be done with either fake requests or responses, or with replays. We consider the fake requests and responses case first. It requires the attacker to send a Binding request to one agent with a source IP address and port for the false candidate. In addition, the attacker needs to wait for a Binding request from the other agent and generate a fake response with a XOR-MAPPED-ADDRESS attribute containing the false candidate. Like the other attacks described here, this attack is mitigated by the STUN message integrity mechanisms and secure candidate exchanges. Forcing the false peer-reflexive candidate result with packet replays is different. The attacker waits until one of the agents sends a check. It intercepts this request and replays it towards the other agent with a faked source IP address. It also needs to prevent the original request from reaching the remote agent, by either launching a DoS attack to cause the packet to be dropped or forcing it to be dropped using Layer 2 mechanisms. The replayed packet is received at the other agent, and accepted, since the integrity check passes (the integrity check cannot and does not cover the source IP address and port). It is then responded to. This response will contain a XOR- MAPPED-ADDRESS with the false candidate, and it will be sent to that false candidate. The attacker then needs to receive it and relay it towards the originator.
The other agent will then initiate a connectivity check towards that false candidate. This validation needs to succeed. This requires the attacker to force a false valid on a false candidate. The injecting of fake requests or responses to achieve this goal is prevented using the integrity mechanisms of STUN and the candidate exchange. Thus, this attack can only be launched through replays. To do that, the attacker needs to intercept the check towards this false candidate and replay it towards the other agent. Then, it needs to intercept the response and replay that back as well. This attack is very hard to launch unless the attacker is identified by the fake candidate. This is because it requires the attacker to intercept and replay packets sent by two different hosts. If both agents are on different networks (e.g., across the public Internet), this attack can be hard to coordinate, since it needs to occur against two different endpoints on different parts of the network at the same time. If the attacker itself is identified by the fake candidate, the attack is easier to coordinate. However, if the data path is secured (e.g., using the Secure Real-time Transport Protocol (SRTP) [RFC3711]), the attacker will not be able to process the data packets, but will only be able to discard them, effectively disabling the data stream. However, this attack requires the agent to disrupt packets in order to block the connectivity check from reaching the target. In that case, if the goal is to disrupt the data stream, it's much easier to just disrupt it with the same mechanism, rather than attack ICE. 19.3. Attacks on Server-Reflexive Address Gathering ICE endpoints make use of STUN Binding requests for gathering server- reflexive candidates from a STUN server. These requests are not authenticated in any way. As a consequence, there are numerous techniques an attacker can employ to provide the client with a false server-reflexive candidate: o An attacker can compromise the DNS, causing DNS queries to return a rogue STUN server address. That server can provide the client with fake server-reflexive candidates. This attack is mitigated by DNS security, though DNSSEC is not required to address it. o An attacker that can observe STUN messages (such as an attacker on a shared network segment, like Wi-Fi) can inject a fake response that is valid and will be accepted by the client. o An attacker can compromise a STUN server and cause it to send responses with incorrect mapped addresses.
A false mapped address learned by these attacks will be used as a server-reflexive candidate in the establishment of the ICE session. For this candidate to actually be used for data, the attacker also needs to attack the connectivity checks, and in particular, force a false valid on a false candidate. This attack is very hard to launch if the false address identifies a fourth party (neither the initiator, responder, nor attacker), since it requires attacking the checks generated by each ICE agent in the session and is prevented by SRTP if it identifies the attacker itself. If the attacker elects not to attack the connectivity checks, the worst it can do is prevent the server-reflexive candidate from being used. However, if the peer agent has at least one candidate that is reachable by the agent under attack, the STUN connectivity checks themselves will provide a peer-reflexive candidate that can be used for the exchange of data. Peer-reflexive candidates are generally preferred over server-reflexive candidates. As such, an attack solely on the STUN address gathering will normally have no impact on a session at all. 19.4. Attacks on Relayed Candidate Gathering An attacker might attempt to disrupt the gathering of relayed candidates, forcing the client to believe it has a false relayed candidate. Exchanges with the TURN server are authenticated using a long-term credential. Consequently, injection of fake responses or requests will not work. In addition, unlike Binding requests, Allocate requests are not susceptible to replay attacks with modified source IP addresses and ports, since the source IP address and port are not utilized to provide the client with its relayed candidate. Even if an attacker has caused the client to believe in a false relayed candidate, the connectivity checks cause such a candidate to be used only if they succeed. Thus, an attacker needs to launch a false valid on a false candidate, per above, which is a very difficult attack to coordinate. 19.5. Insider Attacks In addition to attacks where the attacker is a third party trying to insert fake candidate information or STUN messages, there are attacks possible with ICE when the attacker is an authenticated and valid participant in the ICE exchange.
20. IANA Considerations The original ICE specification registered four STUN attributes and one new STUN error response. The STUN attributes and error response are reproduced here. In addition, this specification registers a new ICE option. 20.1. STUN Attributes IANA has registered four STUN attributes: 0x0024 PRIORITY 0x0025 USE-CANDIDATE 0x8029 ICE-CONTROLLED 0x802A ICE-CONTROLLING 20.2. STUN Error Responses IANA has registered the following STUN error-response code: 487 Role Conflict: The client asserted an ICE role (controlling or controlled) that is in conflict with the role of the server. 20.3. ICE Options IANA has registered the following ICE option in the "ICE Options" subregistry of the "Interactive Connectivity Establishment (ICE)" registry, following the procedures defined in [RFC6336]. ICE Option name: ice2 Contact: Name: IESG Email: firstname.lastname@example.org Change Controller: IESG Description: The ICE option indicates that the ICE agent using the ICE option is implemented according to RFC 8445. Reference: RFC 8445
21. Changes from RFC 5245 The purpose of this updated ICE specification is to: o Clarify procedures in RFC 5245. o Make technical changes, due to discovered flaws in RFC 5245 and feedback from the community that has implemented and deployed ICE applications based on RFC 5245. o Make the procedures independent of the signaling protocol, by removing the SIP and SDP procedures. Procedures specific to a signaling protocol will be defined in separate usage documents. [ICE-SIP-SDP] defines ICE usage with SIP and SDP. The following technical changes have been done: o Aggressive nomination removed. o The procedures for calculating candidate pair states and scheduling connectivity checks modified. o Procedures for calculation of Ta and RTO modified. o Active checklist and Frozen checklist definitions removed. o 'ice2' ICE option added. o IPv6 considerations modified. o Usage with no-op for keepalives, and keepalives with non-ICE peers, removed. 22. References 22.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, <https://www.rfc-editor.org/info/rfc4941>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, DOI 10.17487/RFC5389, October 2008, <https://www.rfc-editor.org/info/rfc5389>. [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)", RFC 5766, DOI 10.17487/RFC5766, April 2010, <https://www.rfc-editor.org/info/rfc5766>. [RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for Interactive Connectivity Establishment (ICE) Options", RFC 6336, DOI 10.17487/RFC6336, July 2011, <https://www.rfc-editor.org/info/rfc6336>. [RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, <https://www.rfc-editor.org/info/rfc6724>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. 22.2. Informative References [ICE-SIP-SDP] Petit-Huguenin, M., Nandakumar, S., and A. Keranen, "Session Description Protocol (SDP) Offer/Answer procedures for Interactive Connectivity Establishment (ICE)", Work in Progress, draft-ietf-mmusic-ice-sip-sdp-21, June 2018. [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, <https://www.rfc-editor.org/info/rfc1918>. [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, <https://www.rfc-editor.org/info/rfc2475>. [RFC3102] Borella, M., Lo, J., Grabelsky, D., and G. Montenegro, "Realm Specific IP: Framework", RFC 3102, DOI 10.17487/RFC3102, October 2001, <https://www.rfc-editor.org/info/rfc3102>.
[RFC3103] Borella, M., Grabelsky, D., Lo, J., and K. Taniguchi, "Realm Specific IP: Protocol Specification", RFC 3103, DOI 10.17487/RFC3103, October 2001, <https://www.rfc-editor.org/info/rfc3103>. [RFC3235] Senie, D., "Network Address Translator (NAT)-Friendly Application Design Guidelines", RFC 3235, DOI 10.17487/RFC3235, January 2002, <https://www.rfc-editor.org/info/rfc3235>. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, <https://www.rfc-editor.org/info/rfc3261>. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002, <https://www.rfc-editor.org/info/rfc3264>. [RFC3303] Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A., and A. Rayhan, "Middlebox communication architecture and framework", RFC 3303, DOI 10.17487/RFC3303, August 2002, <https://www.rfc-editor.org/info/rfc3303>. [RFC3424] Daigle, L., Ed. and IAB, "IAB Considerations for UNilateral Self-Address Fixing (UNSAF) Across Network Address Translation", RFC 3424, DOI 10.17487/RFC3424, November 2002, <https://www.rfc-editor.org/info/rfc3424>. [RFC3489] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)", RFC 3489, DOI 10.17487/RFC3489, March 2003, <https://www.rfc-editor.org/info/rfc3489>. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, July 2003, <https://www.rfc-editor.org/info/rfc3550>. [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, DOI 10.17487/RFC3605, October 2003, <https://www.rfc-editor.org/info/rfc3605>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, DOI 10.17487/RFC3711, March 2004, <https://www.rfc-editor.org/info/rfc3711>. [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004, <https://www.rfc-editor.org/info/rfc3725>. [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2004, <https://www.rfc-editor.org/info/rfc3879>. [RFC4038] Shin, M-K., Ed., Hong, Y-G., Hagino, J., Savola, P., and E. Castro, "Application Aspects of IPv6 Transition", RFC 4038, DOI 10.17487/RFC4038, March 2005, <https://www.rfc-editor.org/info/rfc4038>. [RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network Address Types (ANAT) Semantics for the Session Description Protocol (SDP) Grouping Framework", RFC 4091, DOI 10.17487/RFC4091, June 2005, <https://www.rfc-editor.org/info/rfc4091>. [RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session Description Protocol (SDP) Alternative Network Address Types (ANAT) Semantics in the Session Initiation Protocol (SIP)", RFC 4092, DOI 10.17487/RFC4092, June 2005, <https://www.rfc-editor.org/info/rfc4092>. [RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", RFC 4103, DOI 10.17487/RFC4103, June 2005, <https://www.rfc-editor.org/info/rfc4103>. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <https://www.rfc-editor.org/info/rfc4291>. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006, <https://www.rfc-editor.org/info/rfc4566>. [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 2007, <https://www.rfc-editor.org/info/rfc4787>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, DOI 10.17487/RFC5245, April 2010, <https://www.rfc-editor.org/info/rfc5245>. [RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, RFC 5382, DOI 10.17487/RFC5382, October 2008, <https://www.rfc-editor.org/info/rfc5382>. [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, DOI 10.17487/RFC5761, April 2010, <https://www.rfc-editor.org/info/rfc5761>. [RFC6080] Petrie, D. and S. Channabasappa, Ed., "A Framework for Session Initiation Protocol User Agent Profile Delivery", RFC 6080, DOI 10.17487/RFC6080, March 2011, <https://www.rfc-editor.org/info/rfc6080>. [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, <https://www.rfc-editor.org/info/rfc6146>. [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van Beijnum, "DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", RFC 6147, DOI 10.17487/RFC6147, April 2011, <https://www.rfc-editor.org/info/rfc6147>. [RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent, "Computing TCP's Retransmission Timer", RFC 6298, DOI 10.17487/RFC6298, June 2011, <https://www.rfc-editor.org/info/rfc6298>. [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach, "TCP Candidates with Interactive Connectivity Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, March 2012, <https://www.rfc-editor.org/info/rfc6544>. [RFC6928] Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis, "Increasing TCP's Initial Window", RFC 6928, DOI 10.17487/RFC6928, April 2013, <https://www.rfc-editor.org/info/rfc6928>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis", RFC 7050, DOI 10.17487/RFC7050, November 2013, <https://www.rfc-editor.org/info/rfc7050>. [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy Considerations for IPv6 Address Generation Mechanisms", RFC 7721, DOI 10.17487/RFC7721, March 2016, <https://www.rfc-editor.org/info/rfc7721>. [RFC7825] Goldberg, J., Westerlund, M., and T. Zeng, "A Network Address Translator (NAT) Traversal Mechanism for Media Controlled by the Real-Time Streaming Protocol (RTSP)", RFC 7825, DOI 10.17487/RFC7825, December 2016, <https://www.rfc-editor.org/info/rfc7825>. [RFC8421] Martinsen, P., Reddy, T., and P. Patil, "Interactive Connectivity Establishment (ICE) Multihomed and IPv4/IPv6 Dual-Stack Guidelines", RFC 8421, DOI 10.17487/RFC8421, July 2018, <https://www.rfc-editor.org/info/rfc8421>. [WebRTC-IP-HANDLING] Uberti, J. and G. Shieh, "WebRTC IP Address Handling Requirements", Work in Progress, draft-ietf-rtcweb-ip- handling-09, June 2018.