Apart from the
Question of syntactical correctness of sending an unsolicited label map there
is another problem.
There are cases in
which DoD vs DU distribution and Ordered vs Independent
control
become rather vague
distinctions. That is the problem hidden behind the fact
that
people talk past
each other on this topic, rather than talking to each other.
Rather than talking
about the gross terms, consider the details of
implementation
you are likely to
encounter. If the negotiated mode between two LSRs is DoD,
then
each LSR is required
to accept one or more Label Request messages for each FEC
and neither is
required to accept _any_
unsolicited Label Mapping messages. The
LSR that receives an
unsolicited Label Mapping may decide to immediate release
it - or worse yet -
it may assume the peer has become confused and tear down the
LDP session. This is
in essence the problem that Vijay is probably concerned
with.
However, there is
always the robust notion of being generous in what you
accept.
While, IMHO, the LSR
that sends an unsolicited Label Mapping when in DoD mode
is generally in the
wrong, it seems _very_
un-robust behavior to terminate the LDP
session and it might
be more robust to at least retain the new Label Mapping
(yes,
even if in
conservative retention mode - thus blurring another distinction). In
fact,
it is likely that
some implementations will treat such an unsolicited Label
Mapping
as an implied Label
Withdraw (though - with effort - I can dredge up an old
E-Mail
message in which
members of the LDP design team were adamant that this was
not the way it is
intended to work).
In the case Kannan
is pointing out, the retention of the new Label Mapping (in
case
the previous one is
withdrawn) is very much more robust than almost anything else
you might do (with
the possible exception of using it as an implied Withdraw).
If
the new Label
Mapping is not retained, then the LSP is removed edge to edge
and
must be
re-established.
[Ramia, Kannan
Babu] here i am using the Label Withdraw message (which is again
doesnt lose any context) as my implied Label mapping message in addition to
its withdrawing function, but here only difference is that implied label
mapping may not have any out standing label request so in the sense it is
unsolicited label mapping. But in this case the main difference will be this
label mapping is not a pure Unsolicited case because it has the context of the
LSP it refers. so i dont see this procedural changes should not confuse the
LSRs operating in DOD ordered mode.
This - by the way -
is exactly the behavior originally intended in the DoD, Ordered
control mode: LSR A
in Kannan's case would Withdraw all Labels associated with
forwarding toward
the newly discovered peer LSR C and then wait for all
affected
ingress LSRs to send
Label Requests to re-establish LSPs. I brought this up with
the LDP design team
3 years ago and many of them agreed that this would not be
good behavior.
However, it was not clear that any other behavior should be
explicitly
specified.