Alcatel-Lucent 7450 - Figure 33: ABR Node Protection Using Dynamic Bypass LSP

MPLS and RSVP
7450 ESS MPLS Guide Page 147
Dynamic bypass protection provides for the automatic computation, signaling, and association
with the primary path of an inter-area P2P LSP to provide ABR node protection. Figure 33
illustrates the role of each node in the ABR node protection using a dynamic bypass LSP.
Figure 33: ABR Node Protection Using Dynamic Bypass LSP
In order for a PLR node within the local area of the ingress LER to provide ABR node protection,
it must dynamically signal a bypass LSP and associate it with the primary path of the inter-area
LSP using the following new procedures:
• The PLR node must inspect the node-id RRO of the LSP primary path to determine the
address of the node immediately downstream of the ABR in the other area.
• The PLR signals an inter-area bypass LSP with a destination address set to the address
downstream of the ABR node and with the XRO set to exclude the node-id of the
protected ABR node.
• The request to CSPF is for a path to the merge-point (i.e., the next-next-hop in the RRO
received in the RESV for the primary path) along with the constraint to exclude the
protected ABR node and the include/exclude admin-groups of the primary path. If CSPF
returns a path that can only go to an intermediate hop, then the PLR node signals the
dynamic bypass and will automatically include the XRO with the address of the protected
ABR node and propagate the admin-group constraints of the primary path into the Session
Attribute object of the bypass LSP. Otherwise, the PLR signals the dynamic bypass
directly to the merge-point node with no XRO object in the Path message.
• If a node-protect dynamic bypass cannot be found or signaled, the PLR node attempts a
link-protect dynamic bypass LSP. As in existing implementation of dynamic bypass
within the same area, the PLR attempts in the background to signal a node-protect bypass
at the receipt of every third Resv refresh message for the primary path.
ABR1_2
P2–Merge Point
P1–PLR
ERO::ABR1_2 [S], P2 [L]
XRO:ABR1_1
ABR2_1
PE1 PE2
al_0240
P3
P2
P1
ABR1_1
ERO: P2 [S], ABR2_1 [S], PE2 [L]
LSP Path Empty
Computed ERO: P1[S], ABR1_1 [S], PE2 [L]
ERO: P3 [S], PE2 [S]