The MPLS-OPS Archive

[Vishal M <vishal_study@yahoo.com>]

Hi again,

After going thru relevant RFC sections one more time,
it appears that I was reading the incorrect portion of
Appendix.

Step LMp3 to LMp7 are if a loop is detected. LMp9 and
above address the no loops scenarios. 

So basically LSR can accept duplicate Label Mappings
with same Fec and label. However, if label is
different, a Label Release should be sent to the
originating LSR.

Sorry for the confusion created...

regards,
Vishal.

===================================================== 



Hi Gopal,

Well, the RFC doesn't use the word "SHOULD"...nor does
it say "MAY". It just says "remove the label from
forwarding use". Pls see LMp.7 below...

thanks,
Vishal.

Following is exert from the RFC 3036:
=======================================
Algorithm:
LMp.1   Does the received label mapping match an
outstanding label request for FEC previously sent to
MsgSource.

If not, goto LMp.3.

LMp.2   Delete record of outstanding FEC label
request.

LMp.3   Execute procedure Check_Received_Attributes
(MsgSource, LabelMapping, RAttributes).
 If No Loop Detected, goto LMp.9.

LMp.4   Does the LSR have a previously received label
mapping for FEC from MsgSource? (See Note 1.)
If not, goto LMp.8.  (See Note 2.)

LMp.5   Does the label previously received from
MsgSource match Label (i.e., the label received in the
message)?  (See Note 3.)
         If not, goto LMp.8.  (See Note 4.)

LMp.6   Delete matching label mapping for FEC
previously received from MsgSource.

LMp.7   Remove Label from forwarding/switching use. 
(See Note 5.)
              Goto LMp.33.

===================================================
      
--- "Gopal@Yahoo" <gnaganab@yahoo.com> wrote:
> Vishal, May be i missed. Where does it say "it
> > should remove the label from the forwarding use"?
> Could you copy/paste as-is?
> Thanhks,
> Gopal
> --- Vishal M <vishal_study@yahoo.com> wrote:
> > Hello,
> > 
> > According to RFC 3036 Appendix A.1.2 (Receive
> Label
> > Mapping), if a LSR receives duplicate Label
> Mapping
> > from the peer (i.e. same fec and label again), it
> > should remove the label from the forwarding use.
> > 
> >              RtrX ---LDP----- Cisco GSR
> > 
> > Using RtrX, I advertise duplicate label mapping to
> > the
> > adjacent Cisco GSR (IOS 12.0(14)ST). I observe
> that
> > Cisco accepts the duplicate Label Mapping. 
> > 
> > It doesn't tear down the existing mapping from its
> > tables (atleast "show mpls ldp bindings" still
> > displays the binding).
> > 
> > I turned on the debugs at cisco (attached below)
> and
> > notice that it does detect the duplicate binding
> but
> > doesn't take any (apparant) action.
> > 
> > Has someone noticed this and could someone please
> > comment on the behavior.
> > 
> > Thanks for your time,
> > 
> > Regards,
> > Vishal.
> > 
> > cisco debug log for FEC: 99.99.12.12/32
> > ==============================================
> > 006889: 1d04h: ldp: Rcvd label mapping msg from
> > 172.19.78.85:0 (pp 0x64E8E138)
> > 006890: 1d04h: tagcon: tibent(99.99.12.12/32):
> > created; remote label learned
> > 006891: 1d04h: tagcon: tibent(99.99.12.12/32):
> label
> > 65544 from 172.19.78.85:0 added
> > 
> > 006892: 1d04h: ldp: Rcvd label mapping msg from
> > 172.19.78.85:0 (pp 0x64E8E138)
> > 006893: 1d04h: tagcon: tibent(99.99.12.12/32):
> label
> > 65544 from 172.19.78.85:0 added
> > 
> > 
> > 
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