The answer is B, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_te_path_setup/configuration/xe-16-12/mp-te-path-setup-xe-17-book/mpls-traffic-engineering-and-enhancements.html The MPLS traffic engineering feature does not support routing and signaling of LSPs over unnumbered IP links. So do not configure the feature over those links.

The constraints of MPLS TE Tunnel is not supporting Qos aware, DS-TE does support Qos aware Tunneling. The correct answer is A

Kind of leaning toward answer D because Cisco currently supports only Type 10 LSAs, which have area-local scopes and are flooded within the area.

I found it, it's B The MPLS traffic engineering feature does not support routing and signaling of LSPs over unnumbered IP links. Therefore, do not configure the feature over those links. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_te_path_setup/configuration/xe-3s/mp-te-path-setup-xe-3s-book/mp-te-enhance-xe.html#GUID-96C9B528-9D61-4E5E-83EE-3BA1631A34CB

A should be the correct answer. You need MPLS DS-TE. MPLS traffic engineering allows constraint-based routing (CBR) of IP traffic. One of the constraints satisfied by CBR is the availability of required bandwidth over a selected path. DiffServ-aware Traffic Engineering extends MPLS traffic engineering to enable you to perform constraint-based routing of "guaranteed" traffic, which satisfies a more restrictive bandwidth constraint than that satisfied by CBR for regular traffic. https://www.cisco.com/c/en/us/td/docs/ios/12_2sr/12_2srb/feature/guide/dsteietf.html#wp1053951

I found evidence that seems to point the other way here: https://www.networkworld.com/article/2281049/chapter-4--cisco-mpls-traffic-engineering.html#:~:text=Example%204%2D5%20Definition%20of%20a%20TE%20LSP%20Headend%20in%20Cisco%20IOS Not saying B isn't correct, but I thought I would mention this. I wonder if ios-xe is different than the IOS shown in this article. Always confusing though :P

For every ABR that is running OSPF, do the following steps to configure traffic engineering on each area where you want tunnels in or across. With multiple areas and traffic engineering configured in and across each area, the router can contain changes within the network within an area.

Selected Answer: B The QoS argument is flawed imo, DS-TE is an extension to MPLS-TE that allows that. That means it is no longer a constraint. Even when configured under the MPLS Traffic engineering commands, that would be like saying MPLS-TE can't dynamically create paths because it relies on an IGP. However, the link posted by another user: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_te_path_setup/configuration/xe-16-12/mp-te-path-setup-xe-17-book/mpls-traffic-engineering-and-enhancements.html Clearly states that unnumbered links are not supported. XE 17 is current firmware as well, so it is not outdated. Also to the user that rebuttaled that, unnumbered link is not the same thing as an unnumbed loopback. Even in the documentation linked, the examples have unnumbered loopbacks.

You can span TE tunnels across multiple areas, but not dynamic ones without PCE. Explicit path is supported as well.

Selected Answer: D B is wrong. MPLS TE tunnels can be configured to use IP unnumbered links, often by referencing a loopback interface. Since the question refers to "constraints", the right answer is D: In OSPF, the extensions used to distribute TE information, specifically Opaque LSA type 10, have an area-wide flooding scope. ABRs typically stop this type of LSA, preventing the full TE topology from crossing OSPF area boundaries.