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Difficulty: HardRouting Concepts and Dynamic Routing Protocols

A senior network engineer is designing a multi-protocol enterprise network architecture utilizing both Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs). Which of the following statements correctly describe dynamic routing protocol characteristics and path evaluation behaviors in this environment? (Select TWO)

  1. Internal BGP (iBGP) routes have a default Administrative Distance of 200, causing a router to prefer an internal OSPF route (Administrative Distance of 110) if both protocols advertise the exact same prefix length.Answer
  2. Link-state dynamic routing protocols, such as OSPF, exchange Link-State Advertisements (LSAs) to construct a complete link-state database (LSDB) before running the Dijkstra algorithm to calculate the shortest path tree.Answer
  3. C
    Dynamic routing protocol algorithms evaluate metrics exclusively at Layer 2, appending hop-by-hop MAC address tables to frame headers to complete end-to-end path calculations across WAN boundaries.
  4. D
    Border Gateway Protocol (BGP) neighbors establish peerings using connectionless UDP transport on port 179 to minimize packet encapsulation delay when exchanging full routing tables.

Answer

The statement regarding Internal BGP having an Administrative Distance of 200 compared to OSPF's 110, and the statement regarding link-state protocols building an LSDB via LSAs prior to running the Dijkstra algorithm, are both correct.
The statement concerning Internal BGP (iBGP) is correct because iBGP carries a default Administrative Distance of 200, which is higher (less preferred) than OSPF's default AD of 110 when choosing between equal prefix matches. The statement concerning link-state protocols is also correct because OSPF routers gather topology information via LSAs to populate the local Link-State Database (LSDB) before running the Dijkstra algorithm to calculate optimal routes.

Step-by-Step Solution

1
Evaluate the Administrative Distance relationship between iBGP and OSPF.
OSPF routes have an Administrative Distance (AD) of 110, whereas iBGP routes have an AD of 200. Because lower AD indicates higher trustworthiness, OSPF is preferred over iBGP for equal prefix matches.
Administrative Distance is the first tie-breaker used by the routing table manager when multiple protocols advertise the same prefix.
2
Analyze link-state routing protocol convergence and database synchronization mechanisms.
OSPF routers synchronize their Link-State Database (LSDB) by exchanging Link-State Advertisements (LSAs) and then run Dijkstra's Shortest Path First (SPF) algorithm.
Unlike distance-vector protocols that share routing tables by rumor, link-state protocols require a complete topology map prior to path computation.
3
Verify OSI layer boundaries for routing protocols and BGP transport requirements.
Routing decisions occur at Layer 3 using IP headers, and BGP uses TCP port 179 for reliable peering.
Layer 2 MAC headers change at each router hop, and BGP relies on TCP's connection-oriented guarantees rather than connectionless UDP.

Key Concept

Administrative Distance hierarchy and Link-State Routing Protocol convergence mechanisms
Estimated Time:2m 0s
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Topics

Routing Concepts and Dynamic Routing Protocols

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