The MPLS WG Archive

[Gopala Naganaboyina <gnaganab@yahoo.com>]

It is OK. Out of labels 0 thru 15, 0 thru 3 are
defined with specific function. The Egress router will
give the Implicit-null, explicit-null or any number in
the range depending on the case(implicit-null is more
common. 4 thru 15 are not defined yet but are
reserved. So, interoperability problems may arise in
future if you use them now).

Cheers,
Gopal


Hi,

I have questions for the rsvpte label value.

According to the draft the tunnel 09.txt section 4.1 ,
the contents of a
LABEL is a single label, and encoded in 4 octets.
Each generic MPLS label is an unsigned integer in the
range of through
1048575.  -----> here it does not meantion the
reserved label value.

Suppose there is engress router, is it correct for the
Egress router to
send a resv msg with the label value to be
'00000001'O?
I think it is OK as far as it is within the range as
mentioned in the
draft.

It is OK


But how about the RFC3202. section 2.1, it mentioned
the value for the
label value:

There are several reserved label values:

           i. A value of 0 represents the "IPv4
Explicit NULL Label".
              This label value is only legal at the
bottom of the label
              stack.  It indicates that the label
stack must be popped,
              and the forwarding of the packet must
then be based on the
              IPv4 header.

          ii. A value of 1 represents the "Router
Alert Label".  This
              label value is legal anywhere in the
label stack except at
              the bottom.  When a received packet
contains this label
              value at the top of the label stack, it
is delivered to a
              local software module for processing. 
The actual
              forwarding of the packet is determined
by the label
              beneath it in the stack.  However, if
the packet is
              forwarded further, the Router Alert
Label should be pushed
              back onto the label stack before
forwarding.  The use of
              this label is analogous to the use of
the "Router Alert
              Option" in IP packets [5].  Since this
label cannot occur
              at the bottom of the stack, it is not
associated with a
              particular network layer protocol.

Then if that is the case, the 1 is the reserved one,
it is not correct to
sent out the resv msg with label value '00000001'O or
not?

It is OK. Out of labels 0 thru 15, 0 thru 3 are
defined with specific function. The Egress router will
give the Implicit-null, explicit-null or a any number
>= 16 depending on the situation(implicit-null is more
common).

Cheers,
Gopal


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