RFC 8910

Wed Apr 20 14:57:14 UTC 2022

The server will only send these options if the client asks for them.  In the discover or request packets from the client, have a look at option 55 (parameter request list).  If that list does not contain option 114 or 160 then the server won't send them.  Even if the server did send them without being requested, the client would likely ignore them not knowing what to do with them.

----- Original Message -----
> From: "Ÿnérant" <ynerant at crans.org>
> To: "Users of ISC DHCP" <dhcp-users at lists.isc.org>
> Sent: Wednesday, April 20, 2022 10:04:00 AM
> Subject: RFC 8910

> Hello!

> For my organization, I am using isc-dhcp-server as DHCP server.

> We want to deploy a captive portal for a new open Wifi to authenticate
> users. However, we want to do it great, and avoid to do Man-in-the-
> middle attacks to access the portal. The RFC 8910 let the DHCP server
> to send an API URI that indicates the presence of a captive portal, and
> let the clients to detect the presence of a captive portal and the URL
> that let them to authenticate.

> However, I think that the RFC is not implemented yet. The RFC replaces
> the RFC 7710 (which added a captivep-portal-url option) and the RFC
> 3679, which added a default-url option. The present RFC overwrites this
> option, number 114.

> I just added in my configuration the following options:

> option default-url "https://example.com/api.json"; # 114 from RFC3679
> option v4-captive-portal "https://example.com/api.json"; # 160 from
> RFC7710

> These are recognized by isc-dhcp-server. But when I launch the server
> and add a client, I don't see any of the two options when I analyse the
> DHCP packets (with tcpdump or Wireshark for example). Did I make
> something wrong? Is there something unimplemented?

> One more question: does someone know how clients react to this DHCP
> option? Who really cares about this URL? When is the client informed
> that there is a captive portal, and how is they redirected?

> Regards,

> --
> Yohann D'Anello

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