Cisco Application Centric Infrastructure Fundamentals, Release 3.x and Earlier
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The Cisco Application
Policy Infrastructure Controller (APIC) manages network services. Policies
are used to insert services.
APIC service integration provides a life
cycle automation framework that enables the system to dynamically respond when
a service comes online or goes offline. Shared services that are available to
the entire fabric are administered by the fabric administrator. Services that
are for a single tenant are administered by the tenant administrator.
The
APIC provides automated service insertion
while acting as a central point of policy control.
APIC policies manage both the network
fabric and services appliances. The
APIC can configure the network
automatically so that traffic flows through the services. Also, the
APIC can automatically configure the
service according to the application's requirements. This approach allows
organizations to automate service insertion and eliminate the challenge of
managing all of the complex traffic-steering techniques of traditional service
insertion.
Layer 4 to Layer 7
Policy Model
The Layer 4 to Layer
7 service device type policies includes key managed objects such as services
supported by the package and device scripts. The following figure shows the
objects of the Layer 4 to Layer 7 service device type policy model.
Layer 4 to Layer 7
service policies contain the following:
Services—Contains
metadata for all the functions provided by a device such as SSL offloading and
load-balancing. This MO contains the connector names, encapsulation type, such
as VLAN and VXLAN, and any interface labels.
Device Script—Represents
a device script handler that contains meta information about the related
attributes of the script handler including its name, package name, and version.
Function Profile Group
Container—Objects that contain the functions available to the service
device type. Function profiles contain all the configurable parameters
supported by the device organized into folders.
About Service
Graphs
The Cisco Application Centric
Infrastructure (ACI) treats services as an integral part of an application. Any services that are required are treated as a service graph that
is instantiated on the ACI fabric from the Cisco Application Policy Infrastructure Controller (APIC). Users define the service for the application, while service graphs identify the set of network or service functions that
are needed by the application.
A service graph represents the network using the following elements:
Function node—A function node represents a function that is applied to the traffic, such as a transform (SSL termination,
VPN gateway), filter (firewalls), or terminal (intrusion detection systems). A function within the service graph might require
one or more parameters and have one or more connectors.
Terminal node—A terminal node enables input and output from the service graph.
Connector—A connector enables input and output from a node.
Connection—A connection determines how traffic is forwarded through the network.
After the graph is configured in the APIC, the APIC automatically configures the services according to the service function requirements that are specified in the service graph.
The APIC also automatically configures the network according to the needs of the service function that is specified in the service
graph, which does not require any change in the service device.
A service graph is represented as two or more tiers of an application with the appropriate service function inserted between.
A service appliance (device) performs a service function within the graph. One or more service appliances might be required
to render the services required by a graph. One or more service functions can be performed by a single-service device.
Service graphs and service functions have the following characteristics:
Traffic sent or received by an endpoint group can be filtered based on a policy, and a subset of the traffic can be redirected
to different edges in the graph.
Service graph edges are directional.
Taps (hardware-based packet copy service) can be attached to different points in the service graph.
Logical functions can be rendered on the appropriate (physical or virtual) device, based on the policy.
The service graph supports splits and joins of edges, and it does not restrict the administrator to linear service chains.
Traffic can be reclassified again in the network after a service appliance emits it.
Logical service functions can be scaled up or down or can be deployed in a cluster mode or 1:1 active-standby high-availability
mode, depending on the requirements.
The following figure provides an example of a service graph deployment:
By using a service graph, you can install a service, such as an ASA firewall, once and deploy it multiple times in different
logical topologies. Each time the graph is deployed, ACI takes care of changing the configuration on the firewall to enable the forwarding in the new logical topology.
Deploying a service graph requires bridge domains and VRFs, as shown in the following figure:
Note
If you have some of the legs of a service graph that are attached to endpoint groups in other tenants, when you use the Remove Related Objects of Graph Template function in the GUI, the APIC does not remove contracts that were imported from tenants other than where the service graph is located. The APIC also does not clean endpoint group contracts that are located in a different tenant than the service graph. You must manually
remove these objects that are in different tenants.
About Policy-Based Redirect
Cisco Application Centric
Infrastructure (ACI) policy-based redirect (PBR) enables provisioning service appliances, such as firewalls or load balancers, as managed or
unmanaged nodes without needing a Layer 4 to Layer 7 package. Typical use cases include provisioning service appliances that
can be pooled, tailored to application profiles, scaled easily, and have reduced exposure to service outages. PBR simplifies
the deployment of service appliances by enabling the provisioning consumer and provider endpoint groups to be all in the same
virtual redirect and forwarding (VRF) instance. PBR deployment consists of configuring a route redirect policy and a cluster
redirect policy, and creating a service graph template that uses the route and cluster redirect policies. After the service
graph template is deployed, use the service appliance by enabling endpoint groups to consume the service graph provider endpoint
group. This can be further simplified and automated by using vzAny. While performance requirements may dictate provisioning
dedicated service appliances, virtual service appliances can also be deployed easily using PBR.
The following figure illustrates the use case of redirecting specific traffic to the firewall:
In this use case, you must create two subjects. The first subject permits HTTP traffic, which then gets redirected to the
firewall. After the traffic passes through the firewall, it goes to the Web endpoint. The second subject permits all traffic,
which captures traffic that is not redirected by the first subject. This traffic goes directly to the Web endpoint.
The following figure illustrates a sample ACI PBR physical topology:
The following figure illustrates a sample ACI PBR logical topology:
While these examples illustrate simple deployments, ACI PBR enables scaling up mixtures of both physical and virtual service appliances for multiple services, such as firewalls
and server load balancers.
About Symmetric Policy-Based Redirect
Symmetric policy-based redirect (PBR) configurations enable provisioning a pool of service appliances so that the consumer
and provider endpoint groups traffic is policy-based. The traffic is redirected to one of the service nodes in the pool, depending
on the source and destination IP equal-cost multi-path routing (ECMP) prefix hashing.
The following commands set the redirect policy under the device selection policy connector:
apic1(config-service)# connector external
apic1(config-connector)# svcredir-pol tenant solar name fw-external
Automated Service
Insertion
Although VLAN and
virtual routing and forwarding (VRF) stitching is supported by traditional
service insertion models, the
Application Policy Infrastructure Controller (APIC) can automate service insertion and
the provisioning of network services, such as Secure Sockets Layer (SSL)
offload, server load balancing (SLB), Web Application firewall (WAF), and
firewall, while acting as a central point of policy control. The network
services are typically rendered by service appliances, such as Application
Delivery Controllers (ADCs) and firewalls. The
APIC policies manage both the network
fabric and services appliances. The
APIC can configure the network
automatically so that traffic flows through the services. The
APIC can also automatically configure the
service according to the application's requirements, which allows organizations
to automate service insertion and eliminate the challenge of managing the
complex techniques of traditional service insertion.
About Device
Packages
The Application Policy Infrastructure Controller (APIC) requires a device package to configure and monitor service devices. You add service functions to the APIC through the device package. A device package manages a single class of service devices and provides the APIC with information about the device and its capabilities. A device package is a zip file that contains the following parts:
Device specification
An XML file that defines the following:
Device properties:
Model—Model of the device.
Vendor—Vendor of the device.
Version—Software version of the device.
Functions provided by a device, such as load balancing, content switching, and SSL termination.
Interfaces and network connectivity information for each function.
Device configuration parameters.
Configuration parameters for each function.
Device script
A Python script that interacts with the device from the APIC. APIC events are mapped to function calls that are defined in the device script. A device package can contain multiple device scripts.
A device script can interface with the device by using REST, SSH, or any similar mechanism.
Function profile
Function parameters with default values that are specified by the vendor. You can configure a function to use these default
values.
Device-level configuration parameters
A configuration file that specifies parameters that are required by a device. This configuration can be shared by one or more
graphs using a device.
You can create a device package or it can be provided by a device vendor or Cisco.
The following figure illustrates the interaction of a device package and the APIC:
The functions in a
device script are classified into the following categories:
Device/Infrastructure—For device level configuration and monitoring
Service Events—For
configuring functions, such as a server load balancer or Secure Sockets Layer,
on the device
Endpoint/Network
Events—For handling endpoint and network attach/detach events
The
APIC
uses the device configuration model that is provided in the device package to
pass the appropriate configuration to the device scripts. The device script
handlers interface with the device using its REST or CLI interface.
The device package enables an administrator to automate the management of the following services:
Device attachment and detachment
Endpoint attachment and detachment
Service graph rendering
Health monitoring
Alarms, notifications, and logging
Counters
For more information
about device packages and how to develop a device package, see
Cisco APIC Layer 4 to Layer 7 Device Package Development Guide
About Device
Clusters
A device cluster (also known as a logical device) is one or more
concrete devices that act as a single device. A device cluster has cluster
(logical) interfaces, which describe the interface information for the device
cluster. During service graph template rendering, function node connectors are
associated with cluster (logical) interfaces. The
Application Policy Infrastructure Controller
(APIC)
allocates the network resources (VLAN or Virtual Extensible Local Area Network
[VXLAN]) for a function node connector during service graph template
instantiation and rendering and programs the network resources onto the cluster
(logical) interfaces.
The service graph template uses a specific device that is based on a
device selection policy (called a
logical device context) that an administrator defines.
An administrator can set up a maximum of two concrete devices in
active-standby mode.
To set up a device cluster, you must perform the following tasks:
Connect the concrete devices to the fabric.
Assign the management IP address to the device cluster.
Register the device cluster with the
APIC.
The
APIC
validates the device using the device specifications from the device package.
Note
The APIC does not validate a duplicate IP address that is assigned to two device clusters. The APIC can provision the wrong device cluster when two device clusters have the same management IP address. If you have duplicate
IP addresses for your device clusters, delete the IP address configuration on one of the devices and ensure there are no duplicate
IP addresses that are provisioned for the management IP address configuration.
About Device
Managers and Chassis Managers
A device manager
serves as a single point of configuration for a set of clusters in a
Cisco Application Centric
Infrastructure
(ACI)
fabric. The administration or operational state is presented in the native GUI
of the devices. A device manager handles configuration on individual devices
and enables you to simplify the configuration in the
Application Policy Infrastructure Controller
(APIC).
You create a template in device manager, then populate the device manager with
instance-specific values from the
APIC,
which requires only a few values.
The following figure illustrates a device manager controlling multiple
devices in a cluster:
A chassis manager is a physical or virtual "container" of processing
resources. A chassis manager supports a number of virtual service devices that
are represented as
CDev
objects. A chassis manager handles networking, while
CDev handles processing. A chassis manager enables the
on-demand creation of virtual processing nodes. For a virtual device, some
parts of a service (specifically the VLANs) must be applied to the chassis
rather than to the virtual machine. To accomplish this, the chassis management
IP address and credentials must be included in callouts.
The following figure illustrates a chassis manager acting as a
container of processing resources:
Without a device
manager or chassis manager, the model for service devices contains the
following key managed objects:
MDev—Represents a device type (vendor, model, version).
LDevVIP—Represents a cluster, a set of identically configured devices for Cold Standby. Contains CMgmt and CCred for access to the device.
CDev—Represents a
member of a cluster, either physical or virtual. Contains
CMgmt and
CCred for access to the device.
VDev—Represents a context on a cluster, similar to a
virtual machine on a server.
The following figure
illustrates the model for the key managed objects, with
CMgmt
(management connectivity) and
CCred
(credentials) included:
CMgmt
(host + port) and
CCred
(username + password) allow the script to access the device and cluster.
A device manager and
chassis manager adds the ability to control the configuration of clusters and
devices from a central management station. The chassis adds a parallel
hierarchy to the
MDev
object and
ALDev
object to allow a
CDev
object to be tagged as belonging to a specific chassis. The following managed
objects are added to the model to support the device and chassis manager
concept:
MDevMgr—Represents a type of device manager. An
MDevMgr can manage a set of different
MDevs, which are typically different products from the
same vendor.
DevMgr—Represents a
device manager. Access to the manager is provided using the contained
CMgmt and
CCred managed objects. Each cluster can be associated
with only one
DevMgr.
MChassis—Represents a type of chassis. This managed
object is typically included in the package.
Chassis—Represents a chassis instance. It contains the
CMgmt and
CCred[Secret] managed objects to provide connectivity
to the chassis.
The following figure
illustrates the device manager object model:
The following figure illustrates the chassis manager object model:
About Concrete
Devices
A concrete device can be either a physical device or a virtual device. A concrete device has concrete interfaces. When a concrete
device is added to a logical device, the concrete interfaces are mapped to the logical interfaces. During service graph template
instantiation, VLANs and VXLANs are programmed on concrete interfaces that are based on their association with logical interfaces.
About Function
Nodes
A function node
represents a single service function. A function node has function node
connectors, which represent the network requirement of a service function.
A function node within a service graph can require one or more parameters. The parameters can be specified by an endpoint
group (EPG), an application profile, or a tenant VRF. Parameters can also be assigned at the time that you define a service
graph. The parameter values can be locked to prevent any additional changes.
About Function Node
Connectors
A function node
connector connects a function node to the service graph and is associated with
the appropriate bridge domain and connections based on the graph's connector's
subset. Each connector is associated with a VLAN or Virtual Extensible LAN
(VXLAN). Each side of a connector is treated as an endpoint group (EPG), and
whitelists are downloaded to the switch to enable communication between the two
function nodes.
About Terminal
Nodes
Terminal nodes
connect a service graph with the contracts. You can insert a service graph for
the traffic between two application endpoint groups (EPGs) by connecting the
terminal node to a contract. Once connected, traffic between the consumer EPG
and provider EPG of the contract is redirected to the service graph.
About
Privileges
An administrator can
grant privileges to the roles in the
APIC.
Privileges determine what tasks a role is allowed to perform. Administrators
can grant the following privileges to the administrator roles:
Privilege
Description
nw-svc-connectivity
Create a management EPG
Create management
connectivity to other objects
nw-svc-policy
Create a service graph
Attach a service graph to an
application EPG and a contract
Monitor a service graph
nw-svc-device
Create a device cluster
Create a concrete device
Create a device context
Note
Only an
infrastructure administrator can upload a device package to the
APIC.
Service Automation
and Configuration Management
The Cisco
APIC
can optionally act as a point of configuration management and automation for
service devices and coordinate the service devices with the network automation.
The Cisco
APIC
interfaces with a service device by using Python scripts and calls
device-specific Python script functions on various events.
The device scripts and a device specification that defines functions
supported by the service device are bundled as a device package and installed
on the Cisco
APIC.
The device script handlers interface with the device by using its REST
interface (preferred) or CLI based on the device configuration model.
Service Resource
Pooling
The Cisco ACI fabric
can perform nonstateful load distribution across many destinations. This
capability allows organizations to group physical and virtual service devices
into service resource pools, which can be further grouped by function or
location. These pools can offer high availability by using standard
high-availability mechanisms or they can be used as simple stateful service
engines with the load redistributed to the other members if a failure occurs.
Either option provides horizontal scale out that far exceeds the current
limitations of the equal-cost multipath (ECMP), port channel features, and
service appliance clustering, which requires a shared state.
Cisco ACI can perform
a simple version of resource pooling with any service devices if the service
devices do not have to interact with the fabric, and it can perform more
advanced pooling that involves coordination between the fabric and the service
devices.