Subject: [mpls] What happens to the FECs advertised by LDP when the router is no longer egress for that FEC

From: "Dutta, Pranjal" <[email-masked]>
Date: Thu, 2 Jun 2005 09:37:32 +0530

Hi All,

                    I am a bit not clear on one point from MPLS
Architecture RFC. In downstream unsolicited and ordered control mode,
the egress router takes the initiative for label binding for the FECs
for which it is egress. No let's consider the following simple topology.

        Native IP
-------->R1----mpls------->R2-------mpls-------->R3--------------Native
IP----->R4-----------------Native IP--------->10.171.2..0/24

Here there is an LSP established by LDP from R1 to R3 for FEC
10.171.2.0/24 and R3 is the egress point for the LSP since the FEC is
routed over a native IP interface from R3 (R3->R4->). Now let's say that
we have enabled MPLS in R4 and also in R3---R4 interface. At this point
R4 becomes the egress point for FEC 10.171.2.0/24. Now the question is
at this moment whether R3 will withdraw the local binding for the FEC
and trigger the same in upstream direction through LDP and will wait for
a remote binding from R4 to meet the requirement of ordered control. Or
R3 will still be the egress point till it receives a remote binding from
R4 for the FEC. 

Thanking in advance,

Pranjal

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