draftaamplsldplinkshut00 Anush Mohan anushmohan ericssoncom Anupkumar T anupkumartericssoncom TOPOLOGY All the nodes are LDP enabled We ID: 778902
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Slide1
LDP Behavior in link-down scenariodraft-aa-mpls-ldp-link-shut-00
Anush Mohan
anush.mohan
@ericsson.com
Anupkumar T.
anupkumar.t@ericsson.com
Slide2TOPOLOGY
All the nodes are LDP enabled. We
have the following LDP LSPs to prefix ‘E’ at node ‘B’ Primary LSP(PRE) : B-A-E Backup LSP(BKE) : B-C-D-A-E
A
D
B
C
E
PR
E
BK
E
Slide3OBSERVED INTEROP ISSUE
t0
: physical link between node ‘A’ and
‘B’ is shut t1: ‘B’ receives LDP ‘shutdown’ notification from peer ‘A’. (Messages over tcp session can reach router ‘B’ from ‘A’ as long as some reachability exists from ‘A’ to ‘B’)PRE
A
D
B
C
E
BK
E
shutdown
t0 t1 t2 t3 t4
Sequence of events at LDPd on node ‘B’
Slide4OBSERVED INTEROP ISSUE CONTD.
t2: ‘B’ tears down LDP lsp to prefix ‘E’. Both PR
E
and BKE (which is tied to PRE) are deleted. L2VPN/L3VPN services (on node B) using LDP LSP to node ‘E’ see traffic loss till PRE reconverges (post IGP convergence, t4) t3: ‘B’ receives link down event for B-A physical link t4: LDP LSP (PRE
) reconverges over ‘B-C-D-A-E’ path and traffic resumes
A
D
B
C
E
PR
E
BK
E
t0 t1 t2 t3 t4
Sequence of events at LDPd on node ‘B’
Slide5Possible Solutions
Relax requirement of flushing labels immediately on receiving ‘shutdown’ notification.
LDP needn’t reset session to peer immediately on link ‘down’ event (i.e. when physical connectivity to LDP peer is down). It would be reasonable to wait for LDP hello adjacency timeout.
Slide6Next StepsReview, questions, suggestions are most welcomeWG adoption – post discussion
Thank you!