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300-620 · Question #152

An ACI engineer is implementing a Layer 3 out inside the Cisco ACI fabric that must meet these requirements: - The data center core switch must be connected to one of the leaf switches with a single…

The correct answer is C. Configure the OSPF Protocol policy with an area of 0. To establish a Layer 3 Out (L3Out) with a core switch using a hierarchical link-state routing protocol and 802.1Q tagging, configuring an OSPF Protocol policy with Area 0 is the correct approach. OSPF is a link-state protocol that supports hierarchical design, fulfilling the…

External Network Connectivity

Question

An ACI engineer is implementing a Layer 3 out inside the Cisco ACI fabric that must meet these requirements:

  • The data center core switch must be connected to one of the leaf

switches with a single 1G link.

  • The routes must be exchanged using a link-state routing protocol that

supports hierarchical network design.

  • The data center core switch interface must be using 802.1Q tagging,

and each vlan will be configured with a dedicated IP address. Which set of steps accomplishes these goals?

Options

  • ASet up the ElGRP Protocol policy with the selected Autonomous System number.
  • BSet up the BGP Protocol policy with the Autonomous System number of 0.
  • CConfigure the OSPF Protocol policy with an area of 0.
  • DSet up the ElGRP Protocol policy with the selected Autonomous System number.

How the community answered

(29 responses)
  • A
    3% (1)
  • B
    7% (2)
  • C
    76% (22)
  • D
    14% (4)

Why each option

To establish a Layer 3 Out (L3Out) with a core switch using a hierarchical link-state routing protocol and 802.1Q tagging, configuring an OSPF Protocol policy with Area 0 is the correct approach. OSPF is a link-state protocol that supports hierarchical design, fulfilling the routing requirement.

ASet up the ElGRP Protocol policy with the selected Autonomous System number.

EIGRP (Enhanced Interior Gateway Routing Protocol) is a distance-vector routing protocol, not a link-state protocol, failing to meet the specified routing protocol requirement.

BSet up the BGP Protocol policy with the Autonomous System number of 0.

BGP (Border Gateway Protocol) is a path-vector routing protocol primarily used for inter-AS routing, not an interior gateway link-state protocol suitable for the specified hierarchical data center internal routing requirement; an Autonomous System number of 0 is also generally invalid for BGP.

CConfigure the OSPF Protocol policy with an area of 0.Correct

OSPF (Open Shortest Path Path First) is a link-state routing protocol that inherently supports hierarchical network design through the use of areas, with Area 0 being the backbone area. This directly fulfills the requirement for a link-state protocol with hierarchical design. For 802.1Q tagging with dedicated IP addresses per VLAN, ACI's L3Out configuration supports sub-interfaces or SVI configurations on the border leaf, which align with OSPF for route exchange.

DSet up the ElGRP Protocol policy with the selected Autonomous System number.

EIGRP (Enhanced Interior Gateway Routing Protocol) is a distance-vector routing protocol, not a link-state protocol, failing to meet the specified routing protocol requirement.

Concept tested: ACI L3Out, OSPF for hierarchical routing, protocol selection

Source: https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/5x/l3out-config/cisco-aci-l3out-config-guide-50/m-ospf-l3out.html

Topics

#L3Out#OSPF#802.1Q tagging#link-state routing

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