20030
Explanation:
Understanding SR-MPLS Label Calculation
SR-MPLS uses Segment Routing Global Block (SRGB) and Prefix SIDs to assign labels dynamically. The MPLS label for a node's loopback interface is calculated as follows:
MPLS Label=SRGB Base+Prefix SID Index
Where:
* SRGB Base = 20000 (as given in the figure)
* Prefix SID Index = 30 (configured for R3's Loopback1)
Label Calculation:
20000+30=20030
Thus, the MPLS label corresponding to the loopback1 interface of R3 is 20030.
Why the Answer is 20030?
# The SRGB defines the base label range.# Each router is assigned a unique Prefix SID index.# The label is dynamically computed by adding the Prefix SID Index to the SRGB Base.
Why Other Numbers Are Incorrect?
# Any value outside the range 20000-21000
* Would be incorrect because it must be within R3's SRGB range.
# Using the Prefix SID Index directly (30)
* Incorrect because MPLS labels are not assigned directly using Prefix SIDs; they are computed using the SRGB.
# Reference: Huawei HCIE Datacom - SR-MPLS Label Calculation and SRGB