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352-001 · Question #42

Refer to the exhibit. Will traffic sourced from router A and destined for a host on network 10.1.1.0/24 always take the optimal path to that host?

The correct answer is A. No, if router A chooses to forward traffic destined to a host on the 10.1.1.0/24 network to router B,. Traffic from router A to 10.1.1.0/24 is not guaranteed to take the optimal path because forwarding through router B results in a longer or suboptimal route compared to forwarding through router C.

Layer 3 Control Plane

Question

Refer to the exhibit. Will traffic sourced from router A and destined for a host on network 10.1.1.0/24 always take the optimal path to that host?

Options

  • ANo, if router A chooses to forward traffic destined to a host on the 10.1.1.0/24 network to router B,
  • BYes, router A has enough information to always direct traffic to router C when forwarding traffic to
  • CYes, router B will forward the traffic towards 10.1.1.0/24 correctly, if router A chooses that path.
  • DIt doesn't matter which path to a host on 10.1.1.0/24 router A chooses, through router B or router C,
  • EIt depends on the routing protocol.

How the community answered

(30 responses)
  • A
    60% (18)
  • B
    10% (3)
  • C
    3% (1)
  • D
    20% (6)
  • E
    7% (2)

Why each option

Traffic from router A to 10.1.1.0/24 is not guaranteed to take the optimal path because forwarding through router B results in a longer or suboptimal route compared to forwarding through router C.

ANo, if router A chooses to forward traffic destined to a host on the 10.1.1.0/24 network to router B,Correct

If router A load-balances or selects router B as the next-hop toward 10.1.1.0/24, the traffic will traverse a suboptimal path since router B does not have a direct or equally optimal connection to that network. Because router A may not have the granular routing information needed to always distinguish the better path, it can forward traffic through the longer path via router B rather than the optimal path via router C.

BYes, router A has enough information to always direct traffic to router C when forwarding traffic to

Router A does not always have sufficient specific routing information to guarantee it will consistently select router C as the optimal next-hop toward 10.1.1.0/24.

CYes, router B will forward the traffic towards 10.1.1.0/24 correctly, if router A chooses that path.

Router B does not forward traffic toward 10.1.1.0/24 via the optimal path - the path through router B is longer or less efficient than the direct path through router C.

DIt doesn't matter which path to a host on 10.1.1.0/24 router A chooses, through router B or router C,

The two paths through router B and router C are not equivalent in terms of optimality - one results in suboptimal routing, making the choice of path significant.

EIt depends on the routing protocol.

The routing protocol in use does not change the underlying path topology - the suboptimal routing problem through router B exists regardless of which protocol is running.

Concept tested: Suboptimal path selection with multiple next-hop routers

Topics

#path selection#routing optimality#subnet visibility#forwarding decisions

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