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300-620 · Question #260

A network engineer is implementing a Layer 3 Out in the Cisco ACI fabric. The data center core switches must connect to a pair of leaf switches and exchange routes via a routing protocol. In…

The correct answer is A. Configure the OSPF Protocol policy with an area of 0. To meet the requirements for a Cisco ACI L3Out, configuring the OSPF Protocol policy with an area of 0 offers rapid convergence time and low CPU usage for exchanging routes.

External Network Connectivity

Question

A network engineer is implementing a Layer 3 Out in the Cisco ACI fabric. The data center core switches must connect to a pair of leaf switches and exchange routes via a routing protocol. In addition, the implementation must meet these criteria:

  • The external switch interface must use 802.1Q tagging.
  • Access to the Internet for the ACI fabric must be the L3Out.
  • The L3Out must use a routing protocol that has rapid convergence time

and low CPU usage. Which configuration set meets these requirements?

Options

  • AConfigure the OSPF Protocol policy with an area of 0.
  • BConfigure the BGP Protocol policy with the appropriate Autonomous System number.
  • CImplement the IS-IS Protocol policy with the selected Autonomous System number.
  • DImplement the EIGRP Protocol policy with the selected Autonomous System number.

How the community answered

(38 responses)
  • A
    61% (23)
  • B
    24% (9)
  • C
    5% (2)
  • D
    11% (4)

Why each option

To meet the requirements for a Cisco ACI L3Out, configuring the OSPF Protocol policy with an area of 0 offers rapid convergence time and low CPU usage for exchanging routes.

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

OSPF is a link-state routing protocol known for its rapid convergence times and generally low CPU usage, making it an excellent choice for internal routing in a data center environment connected via an ACI L3Out. Configuring Area 0 is the standard backbone area, simplifying initial deployment and fulfilling the specified criteria.

BConfigure the BGP Protocol policy with the appropriate Autonomous System number.

BGP is a path-vector protocol primarily used for inter-autonomous system routing and typically has slower convergence times and higher CPU usage compared to Interior Gateway Protocols (IGPs) like OSPF for internal data center routing.

CImplement the IS-IS Protocol policy with the selected Autonomous System number.

IS-IS is a good link-state protocol but is less commonly deployed in enterprise data centers compared to OSPF, and OSPF directly addresses the rapid convergence and low CPU requirements effectively.

DImplement the EIGRP Protocol policy with the selected Autonomous System number.

EIGRP is known for rapid convergence but was historically Cisco proprietary, and OSPF is often preferred in vendor-neutral environments while still meeting the rapid convergence and low CPU usage criteria for the data center core.

Concept tested: ACI L3Out Routing Protocol Selection

Source: https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/5x/sw/config-guide/l3out/b_Cisco_APIC_Layer_3_Networking_Configuration_Guide_50x/m_configuring_l3out.html

Topics

#L3Out configuration#Routing protocols#OSPF#External connectivity#802.1Q

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