On 22/03/15 21:06, Eric W. Biederman wrote:

ebiederm@xmission.com (Eric W. Biederman) writes:

quoted

Robert Shearman [off-list ref] writes:

quoted

The control plane can advertise labels for neighbours that don't have
an outgoing label. RFC 3032 s3.22 states that either the remaining
labels should be popped (if the control plane can determine that it's
safe to do so, which in light of MPLS-VPN, RFC 4364, is never the case
now) or that the packet should be discarded.

I can not figure out what you are referring to.  There is no section 3.2
in RFC3022.

I have found it.  That is is RFC3021 Section 3.22.  This is something
the code already does.  If the label can not be looked up with
mpls_route_input_rcu the packet is dropped.

No, the existing code handles the lack of an incoming label. s3.22 is 
stating what should be done with the lack of an outgoing label.

Beyond that I believe the rest of my comments still stand.  If you want
to do this explicitly some form of explicit blackhole route needs to be
supported.  Either just allowing a route to be configured with no output
device or an explicit RTN_BLACKHOLE route.

No, that isn't going to address the problem this patch solves.

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Therefore, if the peer is unlabeled and the last label wasn't popped
then drop the packet. The peer being unlabeled is signalled by an
empty label stack. However, implicit-null still needs to be supported
(i.e. penultimate hop popping) where the incoming label is popped and
no labels are put on and the packet can still go out labeled with the
unpopped part of the stack. This is achieved by the control plane
specifying a label stack consisting of the single special
implicit-null value.

As I understand it you want to handle the case for a label for which
there is no next hop, and the packet should be black-holed.

In struct mpls_route such routes are currently represented by routes
that have no network device.  And in rtnetlink should be represented
with routes of type RTN_BLACKHOLE which I do not currently support
parsing.  But that should be simple enough to correc.t

With respect to Implicit NULL it should be an error to accept a route
that has an RTA_NEWDST that includes an implicit NULL.

The rtnetlink is not ldp nor should it have ldp semantics and be made
complicated by those semantics.

This isn't specific to LDP - it is used by MP-BGP as well, or indeed 
would be perfectly valid to be specified in static configuration. As per 
RFC3031 s4.1.5 (https://tools.ietf.org/html/rfc3031#section-4.1.5) this 
signals that penultimate hop popping should be done, as opposed to 
dropping the packet if it would go out as MPLS (s3.22).

Thanks,
Rob

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The semantics of RTA_NEWDST are the labels to push on after the top most
label has been popped off.  I see no reason to include other mechanisms
into that processing when it is easy enough to add or tweak other
attributes to have those semantics.

Certainly it is not something that I think is worth special casing on
the fast path in mpls_forward.