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When SiteLink is enabled, traffic will prefer the path with the lowest AS path prepend count. In this case:
- CE2 prepends its ASN twice before advertising 10.0.0.0/24 to ALD1.
- ALD3 prepends its ASN once before advertising the same prefix to ALD1.
- So ALD1 will prefer the path through CE2, since it has a lower AS path prepend count (2 vs 1).
Figure 7 shows traffic taking the green path through CE4/NY instead of CE2. This is likely because CE4's configuration results in an even lower prepend count.
The blog statement about ALD1 preferring CE2's path is correct, but Figure 7 depicts a different scenario where CE4 provides the optimal path. SiteLink always selects the path with the fewest prepends.
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