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Re: [Captive-portals] I-D Action: draft-ietf-capport-api-01.txt

Hi David,

On Jul 13, 2018, at 9:59 AM, David Bird <[email protected]> wrote:

Hi Tommy,

No doubt, I see the benefits from the UE point of view... and, I can see the value when everything is working just right. 

We want to optimize the cases when things are working "right", but of course also have reasonable behavior when things aren't.

The edge cases the worry me...  as does the deployment / integration. 

- What does the UE do if the API says "Your online" ... but you are not (e.g. Network enforcement indicates captivity) ? (learns to ignore API?)

If the network enforcement indicates captivity, this translates into either (a) failures to access resources, which may or may not be notified with a helpful error; or (b) redirects to portal sites. The UE will not be aware of captivity (or captive-like behavior, since it can't really tell the difference between a real portal and someone redirecting websites) until the user loads some resource, and which point the user may get the landing page in their browser as they do today. This is exactly what happens to us often today, especially when our probes for captivity are defeated. It's not great for the user, but it works (as proven by existing deployments).

- What does the UE do if the API says "Your captive" ... but you are not (the only way you know, really, is that all your friends with older devices or laptops have no issues getting on-line, so you call UE vendor support!!) ?

In this case, the user will see a landing page prompt when they join the network. That's the only "harm" in this scenario. Just like today when the user gets a prompt for a captive network, they can ignore it and stay on the network and continue to use it. I don't view getting a portal page as an issue to getting online; perhaps I see this when I get on an airplane network, or a coffee shop network, and it just gives me extra information about the flight, without restricting my network access.

- After releasing captivity (or starting without captivity) and transitioning back to captive state -- do you agree that indication comes from the network? Or, or is the UE suppose to poll for updates (perhaps based on some expiration in the API) ?

The ultimate enforcement of captivity comes from the network. However, the best way to renew access will be to have a notion of both a "soft lifetime" (when you should try to re-auth) and a "hard lifetime" (when your access is totally revoked). The hard lifetime is the job of the network, but it's often a bit too late to keep existing connections up by that point. The API allows us to have a hint of when the soft lifetime is; this is not a matter of polling, but a way to trigger (perhaps) a local notification to let the user know that they have 5 minutes left, and should renew if they want to stay on the network.

I agree that enforcement isn't the job of the UE, it is the job of the network... But, the examples above, I think, demonstrate that the UE *is* making different decisions concerning enforcement / captivity than non CAPPORT devices...

These decisions, as far as I can tell, are about improving use experience, rather than actually enforcing anything. The UE won't block traffic if it sees the API mark things as captive, etc; but it will be able to give the user better opportunities to interact with the portal.


On Fri, Jul 13, 2018 at 9:17 AM Tommy Pauly <[email protected]> wrote:

On Jul 13, 2018, at 7:58 AM, David Bird <[email protected]> wrote:

Hi Tommy,

Thanks for the reply... See one follow-up inline.

On Mon, Jul 9, 2018 at 4:33 PM Tommy Pauly <[email protected]> wrote:
Hi David,

Thanks for the read-through. Some responses inline!


On Jul 2, 2018, at 7:48 AM, David Bird <[email protected]> wrote:

Some comments (will not be at meeting)

Section 1. The introduction states the purpose of the API as:

   o The state of captivity (whether or not the host has access to the

   o  A URI that a host's browser can present to a user to get out of

   o  An encrypted connection (TLS for both the API and portal URI)

The state of captivity is not all or nothing and being detailed about "captivity" (e.g. listing walled garden resources up front, down to protocol, port, hostnames, etc) will be complex and error prone. The URI for the captive portal can be gotten by RFC 7710. Captivity signaling should be granular; because we can, and it includes more use-cases.

Agreed. The fundamental thing about this API draft is that it is not the exhaustive set of information that the portal may want to communicate to the UE. The example of the state being captive or not is a very simple case, and there can certainly be more values to pass down.

Section 2. The workflow is stated as:

   1.  Provisioning, in which a host discovers that a network has a
       captive portal, and learns the URI of the API server

   2.  API Server interaction, in which a host queries the state of the
       captive portal and retrieves the necessary information to get out
       of captivity

    3.  Enforcement, in which the enforcement device in the network
       blocks disallowed traffic, and sends ICMP messages to let hosts
       know they are blocked by the captive portal

My issue is with the ordering... At step 2, we have Capport compliant devices enforcing themselves.. while non-Capport devices wait for the network enforcement. We have the (likely) scenarios of API server saying one thing (implying "self enforcement"), while the network "Enforcement" is telling the UE something else.... who is right? Answer: always the network.

This workflow is the summary of of the CAPPORT architecture document. I completely agree that the enforcement is handled by the network, which is why this is all in the third step. The API server does not imply enforcement—It's the way for the portal that is doing enforcement to communicate information to the UE.

Non-CAPPORT devices currently do:

1. Provisioning, without knowing about captivity
3. Enforcement via blocking and redirects, in which UE's need to guess what happened

The enforcement is always the network, but the UE can provide a better user experience with 2.

Do you envision CAPPORT devices doing 1, 2, and 3 before notifying the user of captivity? Or, will CAPPORT devices just do 1 and 2 before notifying the user (or attempting to "login")? It is the latter that I would call 'self enforcement' because the client doesn't *know* there is captivity yet. 

Okay, I understand your point better now. You're right that until something goes wrong (3 blocks us) we don't truly *know* that we're captive and traffic will be blocked. However, I'd argue that this doesn't need to be the central point of the user experience going forward.

Once the device has done 1 and 2, it can present the user with some UI with a login page, or other experience. All this guarantees to the device and the user is that they are on some network that provides a portal landing page experience. That landing page can describe what the contract of the network is—maybe it's totally captive, but maybe some services are allowed through without any extra login (like texting on airplanes, which I'm seeing these days). In the future, maybe some network won't even block traffic, but just use this landing page advertisement as a way to get some information to the user.

As an OS vendor implementor, I view the responsibility of the OS as making sure the user sees the portal landing page if it exists, so as to allow the user to interact with the portal to remove captivity. Enforcement or making any guarantees about enforcement is not the job of the UE, it's the job of the network. The OS can choose whether or not to make a network it's default route for Internet traffic based on hints it has about captivity, as well as its experience of traffic working or not, but that's a reactionary step, not one of enforcement.



Section 3.2. I think the JSON keys represent a too narrow view of walled gardens, and while simplicity is good, here it artificially and severely limits use-cases. 

Obviously, the "permitted" field is a boolean, not reflecting the fact the location very likely has freely available resources in the walled garden.

The "expire-date" and "bytes-remaining" will be hard to synchronize with network enforcement... the enforcement function might not be counting *all* bytes (some might be "free"), session expiry could happen because of time and/or data limits - possibly being consumed by multiple concurrent devices/sessions - but also things like Idle Time or software restart (NAS / AP / etc) or a number of reasons

As mentioned above, this is just the basic set of minimal keys. It is intended to be extendable as we flesh out the use cases.

What would be useful in the API, in my opinion, is for the API to provide a sort of validation, authentication, and additional information for and about network notifications.

Yes, I agree! This was partly discussed at the last meeting; when we had the HMAC key to validate network notifications, we decided to remove that until we had further specified the use cases for validating the network notifications.

On Sun, Jul 1, 2018 at 10:35 AM <[email protected]> wrote:

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Captive Portal Interaction WG of the IETF.

        Title           : Captive Portal API
        Authors         : Tommy Pauly
                          Darshak Thakore
        Filename        : draft-ietf-capport-api-01.txt
        Pages           : 7
        Date            : 2018-07-01

   This document describes an HTTP API that allows hosts to interact
   with a Captive Portal system.

The IETF datatracker status page for this draft is:

There are also htmlized versions available at:

A diff from the previous version is available at:

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:

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