[spring] Kathleen Moriarty's Discuss on draft-ietf-spring-segment-routing-13: (with DISCUSS)

[Kathleen Moriarty <[e-mail]>]

Kathleen Moriarty has entered the following ballot position for
draft-ietf-spring-segment-routing-13: Discuss

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DISCUSS:
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While I understand the assumption that following the capabilities of existing
protocols that incorporate similar functionality is okay, I'd like to walk
through the security properties left off in the security considerations section
to prevent tampering and see what can be done to correct that or minimally to
list out the considerations.

There's a few places in the security considerations section to call out
specifically.

Section 8.1:
   "The received information is validated using
   existing control plane protocols providing authentication and
   security mechanisms.  Segment Routing does not define any additional
   security mechanism in existing control plane protocols."

For MPLS what "security mechanisms" are referred to in this text?  It would be
helpful to list any properties explicitly or drop this phrase if there are no
additional security mechanisms.  Since segment routing lists an explicit list
of segments (I see that this can be done with MPLS labels and you note it is
already exposed), why is there no mention of integrity protection and origin
authentication to prevent tampering?  I think EKR's comment is already hinting
at this with his comments on IPv6, but I'd like to see explicit text to
preferably fix this gap in the architecture, but minimally to document it and
the associated security threats that result from this gap for MPLS and IPv6.

Section 8.2:

   "From a network protection standpoint, there is an assumed trust model
   such that any node adding an SRH to the packet is assumed to be
   allowed to do so.  Therefore, by default, the explicit routing
   information MUST NOT be leaked through the boundaries of the
   administered domain.  Segment Routing extensions that have been
   defined in various protocols, leverage the security mechanisms of
   these protocols such as encryption, authentication, filtering, etc."

This document focuses on the same threats as the MPLS use cases with no mention
of tampering or mitigations.  Text should be added to describe how origin
authentication and integrity are provided in the source routing header for IPv6
with the associated threats or to describe this gap if a solution does not
exist.  I have not read the draft referred to at the start of this section, so
I don't know if it addresses the concern or not.  In any case, this document
isn't complete without some text on tampering considerations within your
trusted domain.

Thank you.