Figure 31: Srlg Penalty Weight Operation - Alcatel-Lucent 7450 Manual

Shared Risk Link Groups
Legend:
(1),(2) SRLGs
The primary LSP path includes a link between A and D with SRLG (1) and (2). The bypass around
this link through nodes B and C includes links (a) and (d), which are members of SRLG (1), and
links (b) and (c), which are members of SRLG 2. If the link metrics are equal, then this gives four
ECMP paths from A to D via B and C:
•
•
•
•
Two of these paths include undesirable (from a reliability perspective) link (c). SRLG penalty
weights or costs can be used to provide a tiebreaker between these paths so that the path including
(c) is less likely to be chosen. For example, if the penalty associated with SRLG (1) is 5, and the
penalty associated with SRLG (2) is 10, and the penalty associated with SRLG (3) is 1, then the
cumulative penalty of each of the paths above is calculated by summing the penalty weights for
each SRLG that a path has in common with the primary path:
•
•
•
•
Therefore path (a), (d), (e) is chosen since it has the lowest cumulative penalty.
Penalties are applied by summing the values for SRLGs in common with the protected part of the
primary path.
Page 138
A
(a)(1) (b)(2)
(c)(2)
B
(d)(1)
Primary LSP path

Figure 31: SRLG Penalty Weight Operation

(a), (d), (e)
(a), (c), (e)
(b), (c), (e)
(b), (d), (e)
(a), (d), (e) = 10
(a), (c), (e) = 15
(b), (c), (e) = 20
(b), (d), (e) = 15
(1),(2) D
(e)(3)
uWave
C
24823
7450 ESS MPLS Guide