I
have a solution for this problem.
Basically
if any LSR receives an Label withdraw message from its valid Next hop
neighbor then before propagating to its upstream peers it need to check the
value of the label being withdrawn, if the label happens to be an NULL label
then it should not propagate the label withdraw to its upstream peers. Now
this LSR should now assume itself as an egress for that LSP.
[Vijayanand C - CTD,
Chennai.] What will happen in valid cases when the eggress actually
wants to withdraw label and when u no longer want to switch for that
FEC ?The pennultimate hop should not hold the label in that case.
How will the Phop know for which case the withdraw applies
?
[Ramia, Kannan Babu] Actually here we
are not holding the egress label, we are sending a label release for
the corresponding withdraw message and also i am expecting
only the INGRESS will start the LSP deletion process for any genuine case
(of course assumption is all LSR is configured with the forwarding of the
label release)
Second
one could be there should be a provision to change the label for the
particular FEC. I.e any point of time the valid next hop LSR can advertise a
change of label for that FEC. Here problems are we need to maintain the
context of that advertisement (LM).
[Vijayanand C - CTD, Chennai.] This becomes
unsolicited advertisement.
[Ramia, Kannan Babu] i dont see any problem in this
kind of advertisement, even if u are configured with DOD ordered mode if
any change in hop count or PV, the downstream LSR will anyway
generate a LM with out any outstanding LR. So i want to treat the
change in label also the same way as that of change in hop
count.
A better way would be for the
egress to withdraw the label. However the ingress will not issue a
request unless it is in Independent control. This anyway is
a problem. My suggestin would be - The ingress after sending a release
can issue a fresh request for the label even if its not in independent
control if it still supports label switching on the FEC. I feel
This would be more cleaner .
[Ramia, Kannan Babu] How the ingress
will know that it need to request again or initate LSP establishment once
again for the same FEC (i mean here what criteria or conditions it checks
before it does this again..) because in some genuine cases if egress wants
to remove the LSP then it may lead to infinite
looping.
Vijay
