The Implementing Cisco Application Centric Infrastructure (300-620 DCACI) (300-620)

The purpose of the Overlay Multicast TEP (O-MTEP) in a Cisco ACI Multi-Site deployment is to perform head-end replication for BUM (Broadcast, Unknown unicast, Multicast) traffic.  This common anycast address is shared by all the spine nodes in the same site and is used to replicate BUM traffic across the sites 4 .

To configure a Cisco ACI system to detect network loops for both untagged and tagged traffic and to stop the loop by disabling an interface within 4 seconds, the following configuration must be used:

Enable Mis-Cabling Protocol (MCP) : MCP detects loops from external sources and will err-disable the interface on which Cisco ACI receives its own packet.  This is crucial for preventing loops in the network 1 .

Configure MCP Transmit Frequency : Set the MCP transmit frequency to a value that allows for quick loop detection. The Cisco ACI fabric provides faster loop detection with transmit frequencies from 100 milliseconds to 300 seconds.  To meet the requirement of detecting and stopping a loop within 4 seconds, you would set the transmit frequency to a value less than 4 seconds 2 .

Set Action on Loop Detection : Configure the MCP policies to identify loops and decide how to act upon them.  You can set the policy to generate a syslog message or disable the port upon loop detection 2 .

Implement Error Disabled Recovery Policy : Configure an error disabled recovery policy to automatically re-enable ports that were disabled due to loop detection after a configurable interval 2 .

By implementing these configurations, the Cisco ACI system will be able to detect and stop network loops quickly and efficiently, ensuring network stability and preventing potential disruptions.

References  :=

Cisco APIC Online Help - Loop Detection 2

Cisco ACI Best Practices Quick Summary

In Cisco ACI, a leaf switch learns a source IP or MAC as a remote endpoint when VXLAN traffic arrives on a leaf fabric port from the spine, and the inner source IP is within the range of the bridge domain subnets associated with the leaf. This process is part of the ACI’s COOP (Council Of Oracles Protocol), which ensures that endpoint information is accurately disseminated across the fabric for efficient traffic forwarding.

On the egress leaf switch, when traffic is received from an L3Out,  no source MAC or IP address of the traffic is learned as a remote endpoint 1 .  The Cisco ACI fabric does not learn the IP addresses from the data plane in an L3Out domain; instead, it uses ARP to resolve next-hop IP and MAC relationships to reach the prefixes behind external routers 1 .

When a pre-provision immediacy is used, the policy is downloaded to the Cisco ACI leaf switch and programmed into the hardware policy Content Addressable Memory (CAM) as soon as the change is implemented on the Cisco Application Policy Infrastructure Controller (APIC). This means that the policy is ready on the leaf switch before any endpoints are actually connected.

 The statement about the MTU value of MP-BGP EVPN control plane packets in Cisco ACI that is true for communication between spine nodes in different sites is that by default, spine nodes generate  9000-bytes packets  to exchange endpoints routing information.  As a result, the Inter-Site network should be able to carry  9000-bytes packets 2 .  This ensures that the control plane traffic, which is not VXLAN encapsulated, can be properly handled across the sites 2 .

In a Cisco ACI environment with multiple silent hosts that are often relocated between leaf switches, configuring IP Data-Plane Learning to ‘No’ will minimize the relocation impact and make the ACI fabric relearn the new location of the host faster.  Disabling IP Data-Plane Learning prevents the fabric from learning IP addresses from the data plane, which can speed up the process of relearning host locations when they move 3 .

The COOP (Council Of Oracle Protocol) database is located on each  spine switch  within the Cisco ACI fabric.  The COOP database is responsible for maintaining a consistent copy of endpoint address and location information across the fabric

To ensure that servers supporting only Cisco Discovery Protocol are discovered automatically by the Cisco ACI fabric when connected, the action that must be taken is to Create an override policy that enables Cisco Discovery Protocol after LLDP is enabled in the default policy group