ACI Multi-Pod IPN Requirements: VLAN 4 and OSPF

300-620 By islever Editorial Last updated

Describe Multi-Pod Implement Layer 3 out (excludes transit routing and VRF route leaking)

Short answer

DE Implementing a Multi-Pod ACI fabric requires the IPN network to use VLAN ID 4 for traffic tagging and OSPF as the routing protocol between spines and IPN devices.

Question

What are two requirements for the IPN network when implementing a Multi-Pod ACI fabric? (Choose two.)
  1. EIGRP routing
  2. PIM ASM multicast routing
  3. BGP routing
  4. VLAN ID 4 Correct Answer
  5. OSPF routing Correct Answer

Key Takeaways

The main trap is confusing PIM ASM with PIM Bidir; while multicast is used for BUM traffic, the IPN specifically requires PIM Bidir, not ASM. Additionally, candidates must know that OSPF is the mandated routing protocol, not BGP or EIGRP.

This question covers the specific networking requirements for the Inter-Pod Network (IPN) in a Cisco ACI Multi-Pod deployment, highlighting the necessity of VLAN ID 4 tagging and OSPF routing.

Common mistake: Candidates often incorrectly select PIM ASM (Option B) because they associate multicast with general ACI operations, failing to recognize that Multi-Pod IPN specifically mandates PIM Bidir. Others might mistakenly choose BGP (Option C) due to its common use in large enterprise networks, overlooking the ACI-specific requirement for OSPF.

Expert Analysis

The Inter-Pod Network (IPN) in a Cisco ACI Multi-Pod architecture has specific technical requirements to ensure proper communication between pods. The primary requirements are:

  1. VLAN ID 4: Traffic originated from the spine interfaces is always tagged with an 802.1q VLAN 4 value when connecting to the IPN devices. This is a strict requirement for the sub-interfaces on the spine switches.
  2. OSPF Routing: In the initial release of ACI Multi-Pod fabric, OSPFv2 is the supported routing protocol (in addition to static routing) on the spine interfaces connecting to the IPN devices.

Let's evaluate the options:

  • A. EIGRP routing: Not supported for IPN in ACI Multi-Pod.
  • B. PIM ASM multicast routing: Incorrect. The IPN uses PIM Bidir (Bidirectional), not PIM ASM (Any-Source Multicast). Using PIM ASM would result in inefficiencies or issues with BUM traffic handling across pods.
  • C. BGP routing: Not supported for IPN in ACI Multi-Pod.
  • D. VLAN ID 4: Correct. This is a mandatory tagging requirement for the spine-to-IPN links.
  • E. OSPF routing: Correct. OSPFv2 is the required routing protocol for the IPN links.

Therefore, the two requirements are VLAN ID 4 and OSPF routing.

Official Reference

https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737855.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When studying ACI Multi-Pod configurations, focus on the specific protocols and identifiers mandated by Cisco. Memorize that the IPN relies on OSPF for unicast routing and PIM Bidir for multicast/BUM traffic. Also, remember the hard-coded VLAN ID 4 for spine-to-IPN connections. For exam questions, eliminate options based on these specific constraints rather than general networking knowledge.

Frequently Asked Questions

Why is PIM Bidir used instead of PIM ASM in ACI Multi-Pod IPN?

PIM Bidir is more efficient for handling Broadcast, Unknown Unicast, and Multicast (BUM) traffic across multiple pods. PIM ASM can lead to suboptimal paths and increased state maintenance, which is undesirable in a multi-pod environment.

Can I use BGP for the Inter-Pod Network in ACI Multi-Pod?

No, BGP is not supported for the IPN in ACI Multi-Pod deployments. The official requirement specifies OSPFv2 (or static routing) for connectivity between the spine switches and the IPN devices.

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Community Votes

E
50%
D
25%
B
25%

50% of anonymous learners picked answer E. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 15 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 15

  1. hybersat 👍 21
    I believe DE is correct.. According to https://haystacknetworks.com/cisco-aci-multi-pod-ipn-inter-pod-network-configuration-verification See these snips: The links (interfaces) between the IPN devices and the spine switches must have the following OSPF configuration on the interfaces (as discussed, these are actually the sub-i nterfaces for VLAN-4). ..... Cisco ACI requires\recommends (works best with) bi-dir multicast as we have many sources and many receivers
  2. hybersat 👍 6
    Also, itS PIM Bidir and not PIM ASM that are required for multi pod
  3. thomyohan 👍 4
    Answer : DE The spine interfaces are connected to the IPN devices through point-to-point routed interfaces. However, traffic originated from the spine interfaces is always tagged with an 802.1q VLAN 4 value PIM Bidir used in the IPN network - Since BUM traffic can be originated by all the leaf nodes deployed across Pods, the use of a different PIM protocol (like PIM ASM, for example) would results in the creation of multiple individual (S, G) entries on the IPN devices that may exceed the specific platform capabilities. With PIM Bidir, a single (*, G) entry must be created for a given BD, independently from the overall number of leaf nodes.
  4. memelas 👍 4
    Correct - D and E https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737855.html
  5. thiyagas 👍 4
    Correct Answer is BE
Show 10 more comments
  1. prospio971 👍 3
    When implementing a Cisco ACI Multi-Pod fabric, the Inter-Pod Network (IPN) must meet specific requirements to ensure proper communication and functionality across pods. These requirements include: PIM ASM Multicast Routing: Multicast is required in the IPN to handle BUM (Broadcast, Unknown Unicast, and Multicast) traffic across pods. Specifically, PIM ASM (Protocol Independent Multicast - Any Source Multicast) or PIM Bidirectional is used to replicate BUM traffic between the pods efficiently. OSPF Routing: The IPN must support OSPF (Open Shortest Path First) routing for establishing connectivity between spine nodes and IPN devices. OSPF is used to advertise the TEP (Tunnel Endpoint) pool prefixes between pods and ensure end-to-end IP reachability for VXLAN tunnels.
  2. Smoothey 👍 2
    Uses dot1.q with Vlan4 and OSPF for routing: interface Ethernet1/1.4 description 40G Link to POD1-SPINE-101(1/1) mtu 9150 encapsulation dot1q 4 vrf member fabric-mpod-vrf ip address 192.168.1.253/30 ip ospf network point-to-point
  3. Estevez 👍 2
    D+E B is incorrect, because IPN uses PIM Bidir, not PIM ASM. (https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737855.html)
  4. ostych 👍 1
    D+E D: OSPF support: In the initial release of ACI Multi-Pod fabric, OSPFv2 is the routing protocol (in addition to static routing) supported on the spine interfaces connecting to the IPN devices. E: The spine interfaces are connected to the IPN devices through point-to-point routed interfaces. However, traffic originated from the spine interfaces is always tagged with an 802.1q VLAN 4 value, which implies the need to define and support Layer 3 sub-interfaces on both the spines and the directly connected IPN devices E: "The main reasons for using PIM Bidir in the IPN network are" section states why Bidir is preferred when compared to ASM. PIM ASM is NOT used. https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737855.html#InterPodConnectivityDeploymentConsiderations
  5. rltk8029 👍 1
    D is incorrect!!! Actually found that VLAN4 is not required for both Multi-POD and Multi-Site. Sub-interface is requirement for both. But for Multi-Site is highly recommended sub-if vlan tag 4.
  6. rltk8029 👍 1
    what I mean here its not requirement for all IPN but only for link toward IPN from spine. While PIM ASM and OSPF requirements for routing and multicast delivery.
  7. rltk8029 👍 1
    Answer D is incorrect -its an exam trap. VLAN4 need to be a sub-interface with vlan tag 4 on ACI spine, but not necessary IPN must have the VLAN 4
  8. slogoheinzy 👍 1
    answer is DE - BUT as of 5.2, BGP is allowed as underlay protocol, so strictly speaking, this question has 2 possible answers, DE and CD
  9. rltk8029 👍 1
    ALSO VLAN 4 is for Multi-Site not Multi-POD!!!! this is main reason D is in correct.
  10. Kastel 👍 1
    I believe BE is the correct answer.

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