Subject: [secdir] secdir review of draft-ietf-mpls-special-purpose-labels-05

From: Tom Yu <[email-masked]>
Date: Mon, 10 Mar 2014 17:30:46 -0400

I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG.  These comments were written primarily for the benefit of the
security area directors.  Document editors and WG chairs should treat
these comments just like any other last call comments.

Summary: ready with nits

I believe the Security Considerations section of this document is
reasonable.

Query: I'm not very familiar with MPLS; is the handling of the Entropy
Label Indicator the only situation where a Label Switching Router
would need to inspect (as opposed to hash for load balancing) labels
below the top of the label stack?

I was confused by the explanation of why Label 7 (ELI) has meaning as
both an ordinary Special Label and an Extended Special Purpose Label
until I read RFC 6790.  Perhaps explain that looking for the ELI is
typically the only reason why a LSR would inspect the middle of the
label stack?

Re answer 6 of Section 3:

If an ingress LSR pushes ESPLs onto the label stack, any downstream
LSRs that do not understand ESPLs could erroneously use the ESPLs as
load balancing inputs.  Would it be a good idea to recommend that
ingress LSRs avoid pushing ESPLs onto the label stack if their policy
cannot tolerate variations in downstream load balancing caused by
inappropriate use of the ESPLs as load balancing inputs by downstream
LSRs that don't understand ESPLs?