ACI

DHCP in Cisco ACI

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The Dynamic Host Configuration Protocol (DHCP) automates IP address assignment through a four-step dialogue known as DORA: Discover, Offer, Request, and Acknowledge. This process ensures that clients can join a network without manual IP configuration.

Because DHCP discovery messages are broadcasts, they cannot cross Layer 3 boundaries. A DHCP relay policy may be used when the DHCP client and server are in different subnets. ACI’s built-in DHCP relay function solves this by intercepting the broadcast and forwarding it as a unicast packet to a configured DHCP server.

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EPG vs. ESG

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The evolution of Cisco ACI’s security model from EPGs to ESGs represents a significant maturation of the platform. While EPGs were instrumental in ACI’s original design, their tightly coupled nature presented challenges in large-scale and complex environments. The ESG model directly addresses these limitations by providing a more flexible, scalable, and operationally efficient approach to security.

The ESG’s ability to decouple security policy from forwarding, expand its scope to the VRF level, and leverage dynamic endpoint selectors allows network professionals to align their security posture with business logic in a way that was not previously possible. This shift not only simplifies complex tasks like route leaking and brownfield migrations but also conserves valuable hardware resources.

The decision of whether to primarily utilize EPGs or ESGs hinges on your specific application requirements and design philosophy.

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ACI EPG vs. ESG – Quiz

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Hey there, ACI enthusiasts! Ready to put your knowledge to the test? – Cisco ACI: EPG vs. ESG Quiz! Test your knowledge on the differences between EPGs and ESGs in Cisco ACI.

In the world of Cisco Application Centric Infrastructure (ACI), understanding the subtle but critical differences between network constructs is key to building a robust and secure fabric. While you might be very familiar with Endpoint Groups (EPGs) and their role in defining both forwarding and security policy, ACI 5.0 introduced a new player to the game: Endpoint Security Groups (ESGs).

Are you ready to see if you can tell the difference? Let’s dive in and find out if you’re an EPG expert or an ESG master!

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Chat with Your ACI Fabric

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ACI Fabric, Meet Your AI Assistant: The Dawn of Conversational Network Management. Model Context Protocol (MCP) is A pivotal enabler for the intelligent interaction. MCP is an emerging open standard that functions as a “universal translator” or, more colloquially, a “USB-C port for AI applications”. It provides a standardized method for AI models to connect with diverse external data sources and tools. This protocol standardizes how AI applications can supply crucial context, such as documents, database records, API data, and web search results, to the Large Language Models (LLMs), thereby allowing them to interact meaningfully with external systems.

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Command Your ACI Fabric with Conversation: AI + MCP in Action

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The Model Context Protocol (MCP) is reshaping the way network professionals interact with network infrastructures. Instead of relying on complex CLI commands or APIs, MCP enables natural language communication with the network. APIC-MCP-Server is a Python-based MCP (Model-Context-Protocol) server I developed to enable interactive communication with Cisco ACI fabrics through the APIC. Designed for scalability and intelligence, it allows AI agents to use targeted “tools” to perform specific operations across the network. Built with Python and the FastMCP framework, this server offers a dynamic and extensible interface that can discover and execute a wide range of ACI functions.

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ACI Application Centric Deployment (ACD) and Subnet Sharing with Route Leaking

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1. Overview In Cisco ACI, a powerful feature called route leaking enables applications and services to communicate seamlessly across Virtual Routing and Forwarding (VRF) instances. This allows for efficient data flow within the network infrastructure, even when applications reside in separate VRFs for security or isolation purposes. Route leaking achieves this by sharing routing information

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ACI Data Plane Policing (DPP): A Deep Dive on L3Out Bandwidth Control

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DPP

1. Overview and Core Concepts Data Plane Policing (DPP) is a crucial ACI feature used to manage and restrict bandwidth consumption on specific fabric access interfaces, ensuring efficient and controlled use of network resources. This blog uses an ACI fabric running 5.2(7f) and focuses on Data Plane Policing of l3Out interfaces. Action on Excess Traffic:

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ACI Route Leaking – Shared Services (Network Centric Deployment)

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Cisco ACI (Application Centric Infrastructure) uses route leaking technique to allow routes to be shared between VRFs in the same tenant or in different tenants.

Route leaking reduces routing devices involved in a multiple VRF environment and improve network performance by avoiding traffic to use outside path for inter-VRF communication. But accidental route leaking can happen if manual configuration is used in a scaled environment which may increase the complexity of network operation and troubleshooting.

ACI route leaking is a powerful feature and it’s critical to understand the pros and cons during the design phase to get the most out of it based on the unique requirements of the specific deployment.

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Cisco ACI Contract

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Cisco ACI security architecture is based on allow-list where explicit definition of traffic flow need to be defined. Contract is a foundation for ACI security architecture where communication between EPGs|ESGs is defined. The contract relationship is between ESGs, EPGs (regular or uSig EPGs) or within EPG|ESG for intra-EPG contract.

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Cisco ACI Floating L3Out

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ACI uses L3Out to connect to external L3 domains via routing (dynamic routing protocol or static). There are multiple options and tools to optimize the L3Out for effective L3 communications between ACI and external network services. One of those is Floating L3Out.

Floating L3Out enables engineers to configure L3Out without specifying logical interfaces. Floating L3Out makes configuration, management, and troubleshooting easier. Only specific leaf nodes, called anchor leaf nodes establish routing adjacencies with external routers.

Anchor leaf node – is a leaf node that establish route peering / L3 adjacencies with the external routers. As of Cisco ACI release 6.0(1), the verified scalability number of anchor leaf nodes is 6 per L3Out.

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ACI Multi-site Object Naming Consideration

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Designing ACI multi-site object names should not be an after thought since it has an implication during inter-site communication deployment. When contract with the right scope is applied between site-local EPGs the ACI objects are mirrored on the remote sites. The mirrored objects appear as if they are deployed in each of these sites’ controllers, while only actually being deployed in one of the sites. These mirrored objects are called “shadow” objects and they appear with the same names as the ones that were deployed directly to each site. Because of the shadow objects requirement for inter-site communication between site-local EPGs, this blogs focus on ACI multi-site object naming consideration an engineer need to be aware of.

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ACI Contract Priority

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This blog post will focus on ACI contract priority. Contract is applied in a provider / consumer relationship and a leaf program a security policy (zoning rules) on TCAM (Ternary Content Addressable Memory). Zoning rule entry defines an action (permit, deny, redirect, log) based on the source EPG, the destination EPG, and filter. The source EPG and destination EPG are represented by a unique class ID ( pcTag ). Zoning rules are per VRF, defined with a unique scope and has a priority. The lower the number of the priority, the higher the priority. Zoning rule with the lower value (higher priority) win over zoning rule with a higher value (lower priority). When a traffic between EPGs match more than one zoning rules, the zoning rule priority with some higher level rules is used to decide the action applied on the traffic flow.

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ACI Contract

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The ACI security architecture plays a foundational role toward Zero Trust architecture and Micro Segmentation initiatives in data center. In this blog post ACI contract structure, contract inheritance, contract labels are discussed. EPG|ESG classification, policy enforcement, and ways of deploying contracts from Macro to micro level are also covered.

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Two Arm Load Balancer with ACI PBR destination in an L3out

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When inserting a load balancer into a Cisco ACI fabric, it is important to understand the desired traffic flow, the advantage of using the ACI fabric anycast gateway, the benefit of selective traffic redirection and if DSR is required. Load balancers can be inserted into ACI fabric using the following deployment options. Policy based redirect is a feature to selectively steer traffic to service nodes. PBR with load balancers (one-arm, two-arm) plays a key role on returning traffic back to the same load balancer as the incoming traffic while keeping the client IP as a source IP.

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ACI Custom EPG Name for Simple and Meaningful Port Group Naming

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An EPG with VMM domain association creates a port group on the APIC managed DVS. The name for the port group defaults to ‘Tenant_name|AP_name|EPG_name’. The name, depending on how the tenant, application profile and EPG are named, may not be simple or meaningful for the VMWare admin. The solution is custom EPG name. An EPG can optionally have a custom name with the VMM domain association. Beginning in release 4.2(3), custom EPG name is used to create a port group with a simple and meaningful name when the default ‘Tenant_name|AP_name|EPG_name’ naming doesn’t meet the need of the VMWare admin’s standard.

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One Arm Load Balancer with ACI PBR Destination in an L3out

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One Arm LB with ACI PBR Destination in an L3out - logical drawing

When inserting a load balancer into a Cisco ACI fabric, it is important to understand the desired traffic flow, the advantage of using the ACI fabric anycast gateway, the benefit of selective traffic redirection and if DSR is required. Load balancers can be inserted into ACI fabric using the following deployment options. Policy based redirect is a feature to selectively steer traffic to service nodes. PBR with load balancers (one-arm, two-arm) plays a key role on returning traffic back to the same load balancer as the incoming traffic while keeping the client IP as a source IP.

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One Arm Load Balancer with ACI Policy Based Redirect

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When inserting a load balancer into a Cisco ACI fabric, it is important to understand the desired traffic flow, the advantage of using the ACI fabric anycast gateway, the benefit of selective traffic redirection and if DSR is required. Load balancers can be inserted into ACI fabric using the following deployment options. Policy based redirect is a feature to selectively steer traffic to service nodes. PBR with load balancers (one-arm, two-arm) plays a key role on returning traffic back to the same load balancer as the incoming traffic while keeping the client IP as a source IP.

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Cisco ACI Transit Routing: A Step-by-Step Configuration Guide

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ACI fabric supports transit routing. This feature enables a border leaf to perform bidirectional redistribution between routing domains. A transit traffic can pass from one layer 3 domain to another layer 3 domain through ACI (the ACI acting as a transit between the two layer 3 domains). A transit route is defined to import traffic through a Layer 3 outside network of an L3out where it is to be imported. A different transit route is defined to export traffic through another L3out to the destination routing domain.

The route-maps for import and export route controls are made up of prefix-list matches. Each prefix-list consists of bridge domain (BD), external subnet prefixes in the VRF and the export prefixes that need to be advertised outside. Route control policies are defined in an l3out and controlled by properties and relations associated with the l3Out. APIC uses the enforce route control property of the l3Out to enforce route control directions. The default is to enforce control on export and allow all on import. The default scope for every route is import. These are the routes and prefixes which form a prefix-based EPG…

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