Re: [lisp] Comments to draft-ietf-lisp-te-12

[Dino Farinacci <[e-mail]>]

> On the other hand, the draft proposes the recursive approach that *prepend*s more than one header. I'm confused of the

Only when you need to perserve an outer RLOC based header. Just like MPLS uses service-in-service through an ISP with stacked headers. But I think it would be rarely used in the LISP overlay case.

> *header*. Is the header consisted of outer IP header and LISP header, or just IP header (assuming the IP underlay network)? I want to make it clear whether the writing of 'recursive' means utilizing the TE capabilities of underlay network. (referring to the second example of recursion in 5.2)

The recursive header means this:

(1) First inner header with EIDs is constructed by the host.
(2) Outer header with RLOCs is constructed by the first ITR/RTR/PITR that gets the EID packet.
(3) A second outer header with RLOCs is constructed by any ITR/RTR/PITR that is on path of the RLOC packet.

And (3) is only performed, if that xTR is configured to add a header.

>     • If yes, I would argue that Section 5.2 in RFC 9300 describes the IPv6-in-IPv6 header format but it didn’t include the extensions of IPv6 header. Consequently, underlay TE is not available in this case since segment routing header(RFC 8754) requires the use of extension header. (Unless another IP header that involves extension header is prepended)

Extension headers are not used in general. If, for instance, an ITR/RTR/PITR wanted to add an SRH, a draft would need to be written to say exactly what they do when they want to use an underlay with such capability. But segment-route controls the path the ITR choose FOR THE underlay and not the encapsulation path (overlay path) which LISP-TE specs out.

>     • If no, it says that LISP has to prepend more headers (IP header or LISP header, or both of them). Obviously, it could be not efficient enough. In this case, why not make it a more elegant way, for example, enabling LISP header to carry the RLOC record.  

I am not following your suggestion. The LISP header has specific features like lisp-crypto, nonce-echoing, map-versioning, vpn-identificaion which are relevant to handling the packet and not what header is prepended to the packet. That is a later step after LISP header is prepended.

Note when you prepend an outer IPv4 or IPv6 header in front of a LISP header, it means that header has RLOC addresses in it.

Dino