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Showing posts from December 4, 2019

Cisco ACI - Port Tracking

Cisco ACI - Port Tracking One of the techniques to speed up convergence in case of internal fabric connectivity failures, "port-tracking" feature addresses an outage where a leaf node loses connectivity to "all" the spine nodes in the Cisco ACI fabric. In such a scenario, the hosts that are connected to such a leaf in active-standby setup are usually not aware of such an outage and continue to send traffic to the now isolated leaf. This is where the port-tracking feature brings down all the host facing ports of the isolated leaf node. For the servers that are dual homed to different leafs, this action would ensure that the uplink to the isolated leaf is not considered for forwarding the traffic. The changes can be made as below: System >> System Settings >> Port Tracking

Cisco ACI - CDP and LLDP

Cisco ACI has the concept of Anycast Gateway where the default gateway of the subnet (configured with the Bridge domain) exists on the Leaf devices. Now, more importantly, the anycast gateway / SVI (Switched Virtual Interface) is configured (rather programmed) on only those Leaf switches which have endpoints belonging to that bridge domain. How does Cisco ACI determine whether it should configure an SVI on a particular Leaf? It does this via CDP, LLDP or OpFlex (if the endpoints support it). This would imply, that CDP / LLDP is not just there for operational purposes, but rather, it actually holds a powerful influence on the actual traffic forwarding, unlike traditional switches. CDP uses the usual Cisco CDP timers with an interval of 60s and a holdtime of 120s. LLDP uses the usual LLDP timers with an interval of 30s and a holdtime of 120s. CDP support for Fabric Extenders has started from ACI 2.2 release. For older releases, LLDP should do the trick.

Cisco ACI - Interface Policies

For network guys coming from the traditional switching world, the interface configuration on Cisco ACI is not as simple as putting "switchport xxx" command under interface x/x. Rather there is a huge list of interface policies which needs to be configured, which is then referenced in the Interface policy group and then stitched with the actual interface (Interface selector). The list of interface policies are as follows: LLDP - Link Layer Discovery Protocol CDP - Cisco Discovery Protocol LACP - Link Aggregation Control Protocol Port Speed Storm Control MCP - Mis-Cabling Protocol Now each policy type is already configured with the default configuration. The best practice is to not touch this default configuration but create an explicit policy. For example, I always have an LLDP_ON, LLDP_OFF, CDP_ON, CDP_OFF and so on, configured explicitly for my setup. Explicit policies for each of these policy types also enables you to configure other parameters such as the CDP, LLDP i