Category Archives: 3. Data Center

Study about data center.
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ACI Training Videos

ACI Training Videos

ACI Training Videos help you understand how to deliver software flexibility to modern IT consumption models and ensure agile Data Center network environments. The ACI development team and senior ACI leaders share their experiences and knowledge about the challenges and best practices to maximize the power of scalable centralized automation solutions and policy-driven application profiles within your network environment.

OTV Deployment

Important OTV Features


Extends Layer 2 LANs over any network that supports IP
Designed to scale across multiple data centers

Supports transparent deployment over existing network without redesign
Requires minimal configuration commands (as few as four)
Provides single-touch site configuration for adding new data centers

Preserves existing Layer 3 failure boundaries
Provides automated multihoming
Includes built-in loop prevention

Optimizes available bandwidth, by using equal-cost multipathing and optimal multicast replication


Transparent Interconnection of Lots of Links:

ACI Stretch Fabric Design

  1. Cisco recommend a minimum of 3 APIC Server?
    • Is this per site or possible to have distributive setup which installed on different site? -“We only allow a single APIC in lab/test environments where redundancy is not required.” So meaning you can still use a single server to control the devices? But in this statement “When the connection between two sites is lost, the site with one APIC controller will be in the minority (site 2 in the figure above). When a controller is in the minority, it cannot be the leader for any shards. This limits the controller in site 2 to read only operations; administrators cannot make any configuration changes through the controller in site 2”

So meaning I cannot use a singe APIC server to control the infrastructure?

  1. Split brain condition?
    • What does split brain condition means? Is it for 2 APIC server or This is for multiple sites with distributed APICS?
    • Can give simple scenario that split brain occur?



APIC/Fabric Discovery Process II

In this discovery process, a fabric node is considered active when the APIC and node can exchange heartbeats through the Intra-Fabric Messaging (IFM) process. The IFM process is also used by the APIC to push policy to the fabric leaf nodes.

Fabric discovery happens in three stages. The leaf node directly connected to the APIC is discovered in the first stage. The second stage of discovery brings in the spines connected to that initial seed leaf. Then the third stage processes the discovery of the other leaf nodes and APICs in the cluster.

The diagram below illustrates the discovery process for switches that are directly connected to the APIC. Coverage of specific verification for other parts of the process will be presented later in the chapter.

The steps are:

Link Layer Discovery Protocol (LLDP) Neighbor Discovery
Tunnel End Point (TEP) IP address assignment to the node
Node software upgraded if necessary
Policy Element IFM Setup


During fabric registration and initialization a port might transition to an “out-of-service” state. Once a port has transitioned to an out-of-service status, only DHCP and CDP/LLDP protocols are allowed to be transmitted. Below is a description of each out-of-service issue that may be encountered:

fabric-domain-mismatch – Adjacent node belongs to a different fabric
ctrlr-uuid-mismatch – APIC UUID mismatch (duplicate APIC ID)
wiring-mismatch – Invalid connection (Leaf to Leaf, Spine to non-leaf, Leaf fabric port to non-spine etc.)
adjaceny-not-detected – No LLDP adjacency on fabric port
Ports can go out-of-service due to wiring issues. Wiring Issues get reported through the lldpIf object information on this object can be browsed at the following object location in the MIT: /mit/sys/lldp/inst/if-[eth1/1]/summary.