MPLS and RSVP LSP Traffic Issue
Question
You have configured MPLS and RSVP in your network using all of the Junos defaults. You established an LSP in your network which is reporting an up status but no traffic is using it.
Which two statements reflect potential causes for this issue? (Choose two)
Answers
Explanations
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A. B. C. D.CD
MPLS and RSVP are protocols used for establishing Label Switched Paths (LSPs) in a network. An LSP is a path through the network that is determined by a series of labels assigned to each packet at the ingress point. These labels are used to forward the packet through the network to the egress point.
When an LSP is established in a network, it is important to ensure that traffic is using it. If the LSP is reporting an up status but no traffic is using it, there are several potential causes for this issue:
A. The LSP egress address is a physical interface address: If the LSP egress address is a physical interface address, this means that the traffic is being routed to a specific physical interface rather than through the LSP. In this case, the LSP is not being used at all. This could be because the configuration is incorrect, or because there is an issue with the physical interface or the associated routing.
B. Family MPLS was omitted from the router configurations: If the "family MPLS" configuration was omitted from the routers, the routers will not be able to understand and process MPLS labels. As a result, the LSP will not be used for traffic forwarding, and regular IP routing will be used instead.
C. No BGP routes are being advertised from the remote neighbor: BGP is the protocol used to exchange routing information between different Autonomous Systems (ASes). If there are no BGP routes being advertised from the remote neighbor, this could indicate that the remote neighbor is not advertising the correct routes to the local router. As a result, traffic is not being directed to the LSP and is instead being routed through the regular IP routing table.
D. The LSP egress address does not match the BGP next-hop address: If the LSP egress address does not match the BGP next-hop address, this means that traffic is being routed to a different egress point than the one specified in the LSP. This could be because the configuration is incorrect, or because there is an issue with the BGP routing table.
In conclusion, when an LSP is reporting an up status but no traffic is using it, it is important to check the above potential causes to identify and resolve the issue.
