Router's Packet Type for Requesting Link-State Information
Question
Which packet type does the router use to request up-to-date link-state information?
Answers
Explanations
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A. B. C. D.C
The Juniper Networks Certified Internet Specialist (JNCIS) exam focuses on Juniper Networks technologies, including Junos OS, routing, and switching. Based on this, the question appears to be related to routing protocols that use link-state advertisements (LSAs) to share network topology information between routers.
In a link-state routing protocol, each router builds a complete map of the network by gathering information about the network topology from other routers. This information is then used to calculate the best path to each destination network. To ensure that each router has the most up-to-date information, routers periodically exchange LSAs with each other.
The different types of LSAs used by a routing protocol are as follows:
IIH (Hello) - These packets are used to discover and maintain neighbor relationships between routers. Hello packets are sent periodically to ensure that neighboring routers are still reachable.
LSP (Link-State Packet) - These packets contain information about the state of a router's links, including its neighbors, the cost to reach each neighbor, and the type of link (e.g., point-to-point, broadcast).
PSNP (Partial Sequence Number Packet) - These packets are sent by a router to request missing LSAs from its neighbors. PSNPs are used when a router has received an LSA from a neighbor but is missing one or more LSAs referenced in that LSA's sequence number.
CSNP (Complete Sequence Number Packet) - These packets are sent by a router to provide a complete list of all LSAs in its database. CSNPs are used when a router first establishes a new neighbor relationship or when it needs to synchronize its database with a neighbor's.
Based on the above information, the answer to the question is C. PSNP. Routers use PSNPs to request missing LSAs from their neighbors to ensure that they have the most up-to-date information about the network topology. The other options (A. IIH, B. LSP, and D. CSNP) are also types of LSAs used by routing protocols but are not specifically used to request up-to-date link-state information.
