A Layer 3 VPN customer opened a case that reports connectivity loss with remote sites.
An operations engineer realized this connectivity loss happened after the LDP label filtering was applied.
What is the root cause of this issue?
Click on the arrows to vote for the correct answer
A. B. C. D. E. F.E.
In a Layer 3 VPN, the Provider Edge (PE) routers assign labels to customer routes, which are used to forward the packets between the customer sites. LDP label filtering is a technique used to filter out unnecessary labels to reduce the size of the Label Information Base (LIB) and the amount of label distribution protocol (LDP) traffic.
In this scenario, the customer reported connectivity loss with remote sites after the LDP label filtering was applied. This indicates that the root cause of the issue is related to label allocation. The correct answer depends on which interfaces or loopbacks were not allocated labels.
Option A suggests that labels were not allocated for the P loopbacks, which means that the Provider (P) routers do not have labels to forward traffic to the customer sites. However, this does not explain why the connectivity loss occurred after LDP label filtering was applied.
Option B suggests that labels were not allocated for both the P and PE physical interfaces. This means that the P and PE routers do not have labels to forward traffic between them, resulting in connectivity loss. However, this does not explain why the connectivity loss occurred after LDP label filtering was applied.
Option C suggests that labels were not allocated for the PE loopbacks. This means that the PE routers do not have labels to forward traffic to the customer sites. This could explain why the connectivity loss occurred after LDP label filtering was applied, as the filtering could have removed the labels that were previously allocated.
Option D suggests that labels were not allocated for the PE, P and Route Reflector (RR) physical interfaces. This means that the PE, P and RR routers do not have labels to forward traffic between them, resulting in connectivity loss. However, this does not explain why the connectivity loss occurred after LDP label filtering was applied.
Option E suggests that labels were not allocated for the PE, P and RR loopbacks. This means that the routers do not have labels to forward traffic to the customer sites. This could explain why the connectivity loss occurred after LDP label filtering was applied, as the filtering could have removed the labels that were previously allocated.
Option F suggests that labels were not allocated for the Customer Edge (CE) loopbacks and physical interfaces. This means that the CE routers do not have labels to forward traffic to the provider network, resulting in connectivity loss. However, this does not explain why the connectivity loss occurred after LDP label filtering was applied.
Therefore, the most likely root cause of this issue is option C, where labels were not allocated for the PE loopbacks.