BSCI (Building Scalable Cisco Internetworks) Exam 
Practice Questions: IS-IS Questions
LSP (Link State Packets in IS-IS

Cisco^® Exam ref: 642-801 (BSCI)

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Q2. Routers participating in IS-IS normally flood LSP (Link State Packets) to adjacent neighbors (except on the interface that the LSP was received). The LSPs have a lifetime, a checksum, and a sequence number. What is the lifetime of an LSP that resides in a link-state database?

A. 2 minutes

B. 5 minutes

C. 10 minutes

D. 20 minutes

Ans: D

Explanation: Routers participating in IS-IS normally, flood LSPs (Link State Packets) to adjacent neighbors, except for the interface on which the LSP was received. Note that in a shared media like LAN, a DIS (Designated Intermediate System) is elected, and DIS floods the media with LSPs. There might be several other scenarios where some routers are not allowed to flood the LSPs. The LSPs are used for constructing link state database. The LSPs have a life time of 20 minutes. The LSPs are refreshed by the originator periodically. Note that, LSPs also maintain a checksum and a sequence number.

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