Hi, Please see my comments inline. Den 2018-01-30 kl. 15:34, skrev Christer Holmberg:
Hi, Please see inline. As requested, I include my replies to the comments you already provided earlier.Significant Issues: A. Section 5.2: Lite implementations only utilize host candidates. A lite implementation MUST, for each component of each data stream, allocate zero or one IPv4 candidates. It MAY allocate zero or more IPv6 candidates, but no more than one per each IPv6 address utilized by the host. Since there can be no more than one IPv4 candidate per component of each data stream, if an ICE agent has multiple IPv4 addresses, it MUST choose one for allocating the candidate. If a host is dual-stack, it is RECOMMENDED that it allocate one IPv4 candidate and one global IPv6 address. With the lite implementation, ICE cannot be used to dynamically choose amongst candidates. Therefore, including more than one candidate from a particular scope is NOT RECOMMENDED, since only a connectivity check can truly determine whether to use one address or the other. I find it quite strange that the above text says there can only be single IPv4 based candidate, while for IPv6 a LITE implementation may have one candidate per IPv6 address. Isn't the LITE implication of having multiple candidates for the same address family similar? Yes, IPv6 kind of forces the need for dealing with multiple IPv6 addresses on any host. However, I can see that certain servers will actually be multi-homed in IPv4 and thus can in a sensible way actually have multiple IPv4 candidates, and let the clients select which interface has the best reachability. Can you please be explicit on what in ICE prevents things to work for IPv4 but the same case works for IPv6?This is text from RFC 5245. I agree it is confusing, and unfortunately I don’t have a good answer. I guess my approach would be to suggest that we simply remove the restriction. In addition, there is generic text about dual-stack etc elsewhere, and I don’t see anything ICE lite specific. OLD: "Lite implementations only utilize host candidates. A lite implementation MUST, for each component of each data stream, allocate zero or one IPv4 candidates. It MAY allocate zero or more IPv6 candidates, but no more than one per each IPv6 address utilized by the host. Since there can be no more than one IPv4 candidate per component of each data stream, if an ICE agent has multiple IPv4 addresses, it MUST choose one for allocating the candidate. If a host is dual-stack, it is RECOMMENDED that it allocate one IPv4 candidate and one global IPv6 address. With the lite implementation, ICE cannot be used to dynamically choose amongst candidates. Therefore, including more than one candidate from a particular scope is NOT RECOMMENDED, since only a connectivity check can truly determine whether to use one address or the other." NEW: "Lite implementations only utilize host candidates. With the lite implementation, ICE cannot be used to dynamically choose amongst candidates. Therefore, including more than one candidate from a particular IP address family is NOT RECOMMENDED, since only a connectivity check can Truly determine whether to use one address or the other."
I have read Ben's comment on this issue. I think something needs to be done to avoid the confusion. There are I think two alternatives, either retain the restriction with an added note on why this restriction exists. The second I think is to go with an amended version of the text proposal, possibly with even clearer wording that if you are running multiple addresses in the same family, you should really should be using a full implementation.
I noted that the "NEW" text above needs an amendment, and that is because I think a very important part of what was cut needs to be retained.
It MAY allocate zero or more IPv6 candidates, but no more than one per each IPv6 address utilized by the host.If one generalize this what is missing is the limitation that only a single candidate per IP address utilized by the host can be added by a lite implementation. Using multiple would be redundant, but lets use a direct statement to this affect, rather than a subordinate clause to a MAY statement.
---B. Section 6.1.1: An agent MUST be prepared that the peer might re-determine the roles as part of any ICE restart, even if the criteria for doing so are not fulfilled. This can happen if the peer is compliant with an older version of this specification. What does it mean to be prepared for a peer that re-determine the roles? What is it one MUST do? If the peer changes its role upon an ICE restart, isn't that going to result in a role mismatch? Thus causing yet another ICE restart, where also this peer will re-evalute? Isn't that good enough? Or is it something else it can do?The roles are re-negotiated during the ICE restart: it may, or may not, result in a role mismatch. "Prepared" means that the peer might change its role even though it does not fulfil the 5245bis criteria for being allowed to do so.
Yes, but prepared is not actionable. I guess what you mean is that an implementation MUST accept and perform re-determination of the role initiated by the peer agent, even if the criteria are not fulfilled.
---C. Section 6.1.3: The ICE agent has a state determined by the state of the check lists. The state is Completed if all check lists are Completed, Failed if all check lists are Failed, and Running otherwise. Does failed really require all the checklists to fail, or simply any to fail if the others are completed?If there are one or more completed, the session can still continue. As described in section 8.1.2: "If at least one of the check lists for other data streams is Completed, the controlling agent SHOULD remove the failed data stream from the session while sending updated candidate list to its peer." ---
Okay, so the statement above is actually fulfilled, by pruning the failed checklists through signalling, so that all lists are completed.
I reacted, because it looked like you can actually arrive at a result where some checklists are completed and some are failed. And if I interpret this it should always be considered as running, as more can be done before things are completed.
I guess there is no real need for additional text here. Just a sense from me as a reader that statements looks wrong, even if it isn't.
D. Section 6.1.4.2: I don't know if I misunderstand the algorithm here in the bullet list. To me it appears that it will terminate prior to have initiated all possible tests, as it appears that it will not unfreeze some of the candidate pairs. If one have tests running for a foundation, but all other candidate checks have been started, then the steps are aborted. Is the bullet list rechecked every Ta?No. Whenever Ta fires, one check list in Running state is checked. When all check lists have been checked, it will start over from the top of the list. Or, did I misunderstand your issue?
No, It was unclear that this is re-run every time Ta fires. I think the reason for this is this sentence in step 4.
If this happens for every single check list in the Running state, meaning there are no remaining candidate pairs to perform connectivity checks for, abort these steps.It was unclear to me that this doesn't mean aborting the whole procedure. Because if the requirement is fulfilled then there is nothing to do until the next Ta, which will possible unfreeze another candidate pair in step 2. I would recommend that you reformulate this sentence to make it clear that the processing for this Ta is stopped, and processing will be resumed the next time Ta fires.
---E. Section 7.2.5.2.2. ICMP Error An ICE agent MAY support processing of ICMP errors for connectivity checks. If the agent supports processing of ICMP errors, and if a Binging request generates an ICMP error, the agent SHOULD set the state of the candidate pair to Failed. I am a bit worried by this blanket statement on ICMP errors. I think it should be clarified which ICMP message types that are relevant to consider as errors? I assume Type 3 (Destination Unreachable) but maybe not all responde codes as Codes 4, 11,12 may be addressable in other ways, and likely Type 11 (Time exceeded) with response code 0, response code 1 is not a clear indication of a non working path.This is from RFC 5245. I don’t think the ICE WG should go through all different codes and combinations, and determine what should be considered an error, and what not. If you can provide something (table, guidance etc), we are happy to include it. Otherwise I’d like to keep it as it is, and let implementations deal with it, as at least I am not aware that this would Have caused issues in ICE deployments.
I think we there is a point to clarify that this applies to ICMP messages indicating a non-usable path. So maybe it could be rewritten to something like this:
An ICE agent MAY support processing of ICMP messaging indicating a non-functioning path for connectivity checks. ICMP messages of type 3 (Destination Unreachable) are indicators of a currently non-functioning path. However, the issue can be temporary as it can depend on routing transients, this for example applies to codes 0, 1 and 5. Other messages that appear to indicate non-functioning path such as Type=11 (Time Exceeded) with code=0 (Time to Live exceeded in Transit) are not clear indicator as the IP packets potentially can reach the destination with a larger TTL value set at transmission. Therefore, implementation needs to analyse the different ICMP messages types and codes for which it considers the path as non-functioning. If the agent supports processing of ICMP errors, and if a Binging request generates an ICMP error, the agent SHOULD set the state of the candidate pair to Failed.What also is not addressed in this is the risk of denial of service attacks using spoofed ICMP messages to shutdown certain connectivity checks. The security considerations lack any discussion of this issue. If ICMP processing are retained, I think a recommendation about validation is needed to avoid at least off path attackers from doing these attacks easily. Unfortunately ICMP response will only include the IP/UDP header, thus no data from the STUN messages which would allow verification that the ICMP messages matches an actually sent check.
It may be simplest to recommend against reacting to ICMP errors from both the perspective that it is a risk for denial of service attack, as well as that it represents a risk terminating connectivity checks for a transient issue. From my perspective I expect this to reduce the number of sent connectivity checks very little
---F. Section 7.2.5.2.3. Timeout If the Binding request times out, the ICE agent MUST set the candidate pair state to Failed. Isn't this erroneous? Timeout for the connectivity check is happening when all the (re-)transmissions have timed out, isn't it? or as simple as missing the word "transaction"?Correct. I will change to "Binding request transaction"
Good!
---G. Section 14.3: Num-Of-Pairs: the number of pairs of candidates with STUN or TURN servers. I don't understand this definition. What does "with STUN or TURN servers" mean?
Candidate pairs where the local side is server-reflexive or relay?The text comes from RFC 5245, but I think it’s wrong. There are no pairs during the gathering phase. My suggestion is to change Num-Of-Pairs to Num-Of-Cands, and say: "Num-Of-Cands: the number of server-reflexive and relay candidates"
Sounds good to me.
---H. Section 14.3: Num-Waiting: the number of checks in the check list in the Waiting state. Num-In-Progress: the number of checks in the In-Progress state. Is "the number of checks" only per single checklist or across all the check lists?Per single check list.
Section 14.1 says: "Those formulas scale with N, the number of checks to be performed."But, from my perspective, that number N is not on a single checklist, but for the whole ICE session, i.e. all the checklists. Thus, I think there needs a clarification on why this is per checklist, making it clear why these two things match up.
---I. Section 17.2.3: When VAD is being used, keepalives will be sent during silence periods. I would claim that this is only true for when VAD without any comfort noise is used. A lot of codecs with VAD operations still generates comfort noise on a frequency of a couple packets a second, way more often then the minimal for ICE keep-alives.What about: "In deployments that are not utilizing Voice Activity Detection (VAD), without any comfort noise, the keepalives are never..."
That is also not true. As keep-alives is not expected to be needed for: 1. Continous media withouth any VAD etc.2. Media with VAD, but with comfort noise not allowing intervals to be to long (<=1 second).
=======Minor/Editorial Issues: 1. Section 5.1.2: This section doesn't make it clear that higher priority values are more prioritized over lower values. That really should be defined here. Now that information only becomes evident implicitly in section 5.1.2.1.I suggest the following: "This priority will be used by ICE to determine the order of the connectivity checks and the relative preference for candidates. Higher priority values give more priority over lower values."
Good with me.
---2. Section 2.1. In order to execute ICE, an ICE agent has to identify all of its address candidates. I think this sentence is raising a too high requirement. An ICE agent has attempt to identify as many of the address candidates as possible. The better coverage of the potential candidates the more likely it is to function. I would also argue that there are multiple cases where you will not figure out that there are candidates that you don't know about. An obvious example is in cases of two NATs between the local address realm and the STUN server, the agent can't figure out that there was an address given to the flow in the middle address realm between the two NATs. That can be only learn if the agent has a STUN server in that address realm. Secondly, there are cases where policy may be applied to exclude certain interfaces and their related candidates.I suggest to replace with first sentence and simply say: "In order to execute ICE, an ICE agent identifies and gathers one or more address candidates."
Yes, works fine in this introduction context.
I also noted that this first paragraph and the second has a strange relation. The first part of first paragraph is general, then there is the part of the host candidate. Then the second part starts with STUN and TURN derived candidates. Maybe the first paragraph should be split between the general and the host part, or some other bridging is needed.I suggest to split the first paragraph into two paragraphs, where the second paragraph begins with the "At least one viable candidate뒰� sentence.
Looks like it should work.
---3. Section 2.3: If the transactions above succeed, the agents will set the nominated flag for the pairs, and will cancel any future checks for that component of the data stream. Although what is stated is normal, it is not guaranteed to happen, I know this is intended as a simplified overview, but ignoring that there can occur some shuffling back and forth if high priority checks complete after low priority ones should at least be hinted or at least allowed by the use of words.One of the tasks have been to simplify section 2, because it was too detailed for people who just wanted to get an overview of ICE. For example, we removed the text about role conflicts. So, I would prefer to not cover your case in section 2. I don¹t think it is essential for people who want to get an overview. Implementers obviously will need to read the whole spec.
Okay, I understand the point.
---4. Section 3. As RFC 7825 do describe a significant enough different usage of ICE from SIP, I think it would be good to actually included an informational reference to this usage.I can do that. However, note that RFC 7825 references RFC 5245. It even references specific sections, which may not be the same in 5245bis. In addition, RFC 7825 uses ³aggressive nomination² terminology, which has been removed from 5245bis. What about: "RFC 7825 defines an ICE usage for the Real-Time Streaming Protocol (RTSP). Note, however, that the ICE usage is based on RFC 5245."
Yes, I think that is very fair statement. But there is a point of actually indicating that there are different usages therefore I think it make sense to include that sentence.
---5. Section 5.1.1.4: An ICE agent SHOULD monitor the interfaces it uses, invalidate candidates whose base has gone away, and acquire new candidates as appropriate when new interfaces appear. I am missing discussion of new addresses here. If the base disappears, it might be that there is a new IP address that one should use. That doesn't necessary imply a new interface.What about: "Host candidates do not time out, but the candidate addresses may change or disappear for a number of reasons. An ICE agent SHOULD monitor the interfaces it uses, invalidate candidates whose base has gone away, and acquire new candidates as appropriate when new <new>IP addresses (on new or currently used interfaces)</new> appear."
Looks good to me.
---6. Section 7.2.5.1: If the Binding request generates a 487 (Role Conflict) error response, and if the ICE agent included an ICE-CONTROLLED attribute in the request, the agent MUST switch to the controlling role. If the agent included an ICE-CONTROLLING attribute in the request, the agent MUST switch to the controlled role. I think the first sentence should have a forward reference to Section 7.3.1.1 where the rest of the solution is described.I will add a reference.
Ok
---7. Section 7.3: If the agent is using Diffserv Codepoint markings [RFC2475] in its data packets, it SHOULD apply the same markings to Binding responses. I find this sentence a bit unclear. Is it intended to say: If the agent receiving the binding request, intended to use DSCP markings !=0 for the data, it SHOULD set, the same marking to binding responses. or If the agent receives a binding request with DSCP markings, then it should apply to corresponding code point when forming the binding response?It means that it will use the same markings in Binding responses that it uses in data packets (audio, video, etc).
Okay, I wonder if it is the temporal aspect of the sentence that makes it harder for me to parse correctly.
There are unclarity of which agent is referenced and whom "it" is in the sentence.
It is the STUN server. Would the following be more clear? "If the agent is using Diffserv Codepoint markings [RFC2475] in data packets that it sends, the agent SHOULD apply the same markings to Binding responses." Yes, except that I stumbles "it sends" where it is more likely "it will send" is the correct form.
8. Section 8.3.1: The procedures in Section 8 require that an ICE agent continue to listen for STUN requests and continue to generate triggered checks for a data stream, even once processing for that stream completes. That reference to Section 8, should that in fact be to Section 8.1 specifically? It looks strange with a self reference, which in some aspect a reference to section 8 means.
I think this issue was missed.
---9. Section 15: 4.57566E+18 (note that an implementation would represent this as a 64-bit integer so as not to lose precision). Why the floating point representation? Priorities are integer numbers and thus should be presented as such in this example.This is from RFC 5245, and unfortunately I don’t know.
Can you not just calculate the 64-bit integer and write it out?
---10. Section 17.2.1: First and foremost, ICE makes use of TURN and STUN servers, which would typically be located in the network operator's data centers. Is really network operator's data centers the right entity here? I would claim it is the service operators data centers, they may contract STUN services from network operators, but if the service operator isn't providing any STUN service for its own service, then ICE is unlikely to work.Could we simply say “located in data centers”?
Yes.
---11. Section 18.2: Local IPv6 addresses can be preferred. I think this sentence needs to clarify that it means local to host, rather than any form of relayed or translated address, rather than a local scope only IPv6 address.I could say: "Local IPv6 host addresses"
Maybe better: IPv6 address from the local host can be preferred.
---12. Section 18.5: 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, either in text or binary form within a packet, and rewrite them if they match a binding. Are actually these generic ALG functionality relevant today? They proved to be a very bad idea very quickly. A note that this was a consideration at the time RFC 5245 was published.I don’t know whether the functionality is relevant. But, I guess it doesn’t hurt to have the text.
Fine, I guess it does no real harm. Cheers Magnus Westerlund ---------------------------------------------------------------------- Media Technologies, Ericsson Research ---------------------------------------------------------------------- Ericsson AB | Phone +46 10 7148287 Torshamnsgatan 23 | Mobile +46 73 0949079 SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@xxxxxxxxxxxx ----------------------------------------------------------------------
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