Information About ePBR
Enhanced Policy-based Redirect (ePBR) in Elastic Services Re-direction (ESR) provides traffic redirection and service chaining across the standalone and fabric topologies by leveraging policy-based redirect solution and achieves service chaining without adding extra headers, and avoids latency in using extrra headers.
ePBR enables application-based routing and provides a flexible, device-agnostic policy-based redirect solution without impacting application performance. The ePBR service flow includes the following tasks:
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Configuring ePBR Service and Policy
You must first create an ePBR service which defines the attributes of service end points. Service end points are the service appliances such as firewall, IPS, etc., that can be associated with switches. You can also define probes to monitor the health of the service end points and can define the forward and reverse interfaces where the traffic policies are applied. ePBR also supports load balancing along with service chaining. ePBR allows you to configure multiple service end points as a part of the service configuration.
After creating the ePBR service, you must create an ePBR policy. The ePBR policy allows you to define traffic selection, redirection of traffic to the service end point and various fail-action mechanisms on the end point health failure. You may use IP access-list end points with permit access control entries (ACE) to define the traffic of interest to match and take the appropriate action.
The ePBR policy supports multiple ACL match definitions. A match can have multiple services in a chain which can be sequenced by a sequence number. This allows flexibility to add, insert, and modify elements in a chain in a single service policy. In every service sequence, you can define the fail action method such as drop, forward, and bypass. The ePBR policy allows you to specify source or destination-based load balancing and bucket counts in order to have granular load balancing of traffic.
Applying ePBR to an Interface
After creating the ePBR policy you need to apply the policy on an interface. This allows you to define the interface at which the traffic ingresses into the standalone or Nexus fabric. You can also apply the policy in both the forward and reverse directions. There may only be two IPv4/IPv6 policies applied to the interface, one in the forward and one in the reverse direction.
Creating Bucket and Load Balancing
ePBR computes the number of traffic buckets based on the service that has maximum number of service-end-points in the chain. If you configure the load balance buckets, your configuration will have the precedence. ePBR supports load balancing methods of source IP and destination IP but does not support L4-based source or destination load balancing methods.
ePBR Object Tracking, Health Monitoring, and Fail-Action
ePBR creates SLA and Track objects based on the probe types configured in the service and supports various probes and timers such as ICMP, TCP, UDP, DNS, HTTP. ePBR also supports user defined tracks, which allows you to create tracks with various parameters including milli second probes in associating with ePBR.
ePBR monitors the health of the end points by provisioning IP SLA probes and object tracks to track the IP SLA reachability when you apply the ePBR probe configuration.
You can configure the ePBR probe options for a service or for each of the forward or reverse end points. You can also configure frequency, timeout, retry up and down counts, and source loopback interface so that they can be used for source IP of an IP SLA session. You can define any type of tracks and associate them with the forward or the reverse end points. The same track objects is re-used for all policies using the same ePBR service.
You can define tracks separately and assign the track ID to each service-end point in ePBR. If you do not assign any user-defined track to an endpoint, ePBR will create a track using probe method for the end point. If no probe method is defined at the end point level, the probe method configured for the service level will be used.
ePBR supports the following fail-action mechanisms for its service chain sequences:
Drop on Fail
Bypass of a service sequence indicates that the traffic must be redirected to the next service sequence when there is a failure of the current sequence.
Drop on fail of a service sequence indicates that the traffic must be dropped when all the service-end-points of the service become unreachable.
Forward is the default option and indicates that upon failure of the current service, traffic should use the regular routing tables. This is the default fail-action mechanism.
Symmetry is maintained when fail-action bypass is configured for all the services in the service chain. In other fail-action scenarios, when there are one or more failed services, symmetry is not maintained in the forward and the reverse flow.
ePBR Session-based Configuration
ePBR sessions allow addition, deletion or modification of the following aspects of in-service services or policies. The in-service refers to a service that is associated with a policy that has been applied to an active interface or a policy that is being modified and currently configured on an active interface.
Service endpoints with their interfaces and probes
Reverse endpoints and probes
Matches under policies
Load-balance methods for matches
Match sequences and fail-action
ePBR session ACL refresh allows you to update the policy generated ACLs, when the user-provided ACL gets modified or added or deleted with ACEs. On the refresh trigger, ePBR will identify the policies that are impacted by this change and create or delete or modify the buckets’ generated ACLs for those policies.
For ePBR scale values, see Cisco Nexus 9000 Series NX-OS Verified Scalability Guide.