5- en_ROUTE_v7_Ch05.pdf

Implementing Cisco IP Routing (ROUTE)

Chapter 5: Implementing Path Control

Elaborated by: Ing. Ariel Germán For: ITLA Based on: Foundation Learning Guide CCNP ROUTE 300-101 Diane Teare, Bob Vachon, Rick Graziani 2015 ROUTE v6 Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Chapter 5 Topics  Using Cisco Express Forwarding Switching  Understanding Path Control  Summary

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Using Cisco Express Forwarding Switching

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 Upon completing this section, you will be able to do the following: • Describe the different switching mechanisms that a Cisco router uses • Describe how Cisco Express Forwarding (CEF) works

• Describe how to verify that CEF is working • Describe how to verify the content of the CEF tables • Describe how to enable and disable CEF by interface and globally

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Control and Data Plane  The exchange of routing protocol information is performed in the control plane by the route processor.  Data packets are forwarded in the data plane by an interface microcoded processor.  Control plane and data plane are relatively independent.

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Cisco Switching Mechanisms

 Process switching

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• Is the slowest method. • Every packet is examined by the CPU in the control plane and all forwarding decisions are made in software. • It greatly degrades performance and is generally used only as a last resort or during troubleshooting. © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Cisco Switching Mechanisms

 Fast switching • Is faster than process switching. • The first packet is process switched, subsequent frames in the flow arrive, the destination is found in the hardware fast-switching cache and the frames are then forwarded without interrupting the CPU. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Cisco Switching Mechanisms

 Cisco Express Forwarding • Is the fastest method. • Two tables are created beforehand: Forwarding Information Base (FIB) and adjacency table. • The contain all the information the router need to consider when forwarding the packet. 8

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Process and Fast Switching  An EIGRP update containing a new route to 10.0.0.0/8 is added to the EIGRP topology table.

 Process switching might trigger an ARP request or find the Layer 2 address in the ARP cache.

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Cisco Express Forwarding  It caches the information that is generated by the Layer 3 routing engine even before the router encounters any data flows.  The control plane is responsible for building the FIB table and adjacency tables in software.  The data plane is responsible for forwarding IP unicast traffic using hardware.  The FIB is arranged for maximum lookup speed (most specific entry first).

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Cisco Express Forwarding

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Analyzing Cisco Express Forwarding

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Analyzing Cisco Express Forwarding

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Analyzing Cisco Express Forwarding

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Enable and Disable CEF by Interface and Globally

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Understanding Path Control

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 Upon completing this section, you will be able to do the following: • Identify the need for path control. • Describe how to use policy-based routing (PBR) to control path selection. • Describe how to use IP service-level agreement (IP SLA) to control path selection.

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The Need for Path Control  Path control is required to avoid performance issues and to optimize paths.

 Path control tools can be used to change the default destination forwarding and optimize the path of the packets for some specific application.

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Implementing Path Control Using Policy-Based Routing  PBR enables the administrator to define a routing policy other than basic destination-based routing using the routing table.  With PBR, route maps can be used to match source and destination addresses, protocol types, and end-user applications.  When a match occurs, a set command can be used to define items, such as the interface or next-hop address to which the packet should be sent.

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PBR Features  PBR adds flexibility in a difficult-to-manage environment by providing the ability to route traffic that is based on network needs.

 Benefits of implementing PBR in a network include the following: • • • •

Source-based transit-provider selection QoS Cost savings Load sharing

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Steps for Configuring PBR 1. Enable PBR by configuring a route map using the route-map global configuration command. 2. Implement the traffic-matching configuration, specifying which traffic will be manipulated. This is done using the match commands. 3. Define the action for the matched traffic. This is done using the set commands. 4. Optionally, fast-switched PBR or CEF-switched PBR can be enabled. 5. Apply the route map to incoming traffic or to traffic locally generated on the router.

6. Verify PBR configuration with basic connectivity and path verification commands

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Configuring PBR  The route-map map-tag [permit | deny] [sequencenumber] global configuration command is used to create a route map. • If the statement is marked as permit, packets that meet all the match criteria are policy-based routed. • If the statement is marked as deny, packet meeting the match criteria is not policy-based routed. Instead, it is sent through the normal forwarding channels and destination-based routing. • If no match is found in the route map, the packet is not dropped. It is forwarded through the normal routing channel • Note: To drop a packet, forward it to the interface null 0. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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PBR match Commands  The match condition route map configuration commands are used to define the conditions to be checked. • match ip address {access-list-number | name} [...access-list-number | name] | prefix-list prefix-list-name [..prefix-list-name] • match length min max Matches based

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PBR set Commands  If the match statements are satisfied, you can use the set ip next-hop or set interface commands. • set ip next-hop ip-address [...ip-address] • set interface type number [...type number]

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Configuring PBR on an Interface  To identify a route map to use for policy routing on an interface, use the ip policy route-map map-tag interface configuration command.  Remember that policy-based routing is configured on the interface that receives the packets, not on the interface from which the packets are forwarded.

 Packets originating on the router are not normally policy routed.  To identify a route map to use for local policy routing, use the ip local policy route-map map-tag global configuration command. • This command applies the specified route map to packets originating on the router. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Verifying PBR  To display the route maps used for policy routing on the router’s interfaces, use the show ip policy EXEC command.

 To display configured route maps, use the show route-map [map-name] EXEC command.  Use the debug ip policy EXEC command to display IP policy routing packet activity.

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Configuring PBR Example

 In the example, you will: • Verify normal traffic paths as selected by the traditional destinationbased routing. • Configure PBR to alter the traffic flow for one client station. • Verify both the PBR configuration and the new traffic path Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Verify Normal Traffic Paths

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Configure PBR to Alter the Traffic Flow from the Notebook

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Verify the PBR Configuration and Traffic Path

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Verify the PBR Configuration and Traffic Path

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Verify the PBR Configuration and Traffic Path

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Verify the PBR Configuration and Traffic Path

Notebook

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Implementing Path Control Using Cisco IOS IP SLAs  PBR is a static path control mechanism.  It cannot respond dynamically to changes in network health.

 If a policy states that when packet loss on primary exceeds 5%, backup should be used, It can´t be done with PBR alone. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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IP SLA Features  Cisco IOS IP SLAs perform network performance measurement within Cisco devices.  Cisco IOS IP SLAs actively send simulated data across the network to measure performance between multiple network locations or across multiple network paths.  The information collected includes data about: • • • • • • • •

Response time One-way latency Jitter Packet loss Voice-quality scoring Network resource availability Application performance Server response time.

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Cisco IOS IP SLA Sources and Targets  All the IP SLA measurement probe operations are configured on the IP SLAs source, such as a Cisco IOS router.

 If the target is another Cisco IOS device, the target can be configured as an IP SLA responder. A responder can provide accurate measurements without the need for dedicated probes or any complex or per-operation configuration.

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Cisco IOS IP SLA Operations  An IP SLA operation is a measurement that includes protocol, frequency, traps, and thresholds.  This operation can be used with both types of target devices (source and responder).  When the operation is finished and the response has been received, the results are stored in the IP SLA MIB on the source.  These results can be retrieved and viewed using command line interface (CLI) commands or using Simple Network Management Protocol (SNMP). Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Cisco IOS IP SLA Operation with Responders  Using an IP SLA responder provides enhanced measurement accuracy and additional statistics that are not otherwise available via standard ICMP-based measurement.  When a network manager configures an IP SLA operation on the IP SLA source, reaction conditions can also be defined.

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Steps for Configuring IP SLAs  The following steps are required to configure Cisco IOS IP SLAs functionality: 1. Define one or more IP SLA operations (or probes). 2. Define one or more tracking objects to track the state of IOS IP SLA operations. 3. Define the action associated with the tracking object.

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Step 1: Configuring Cisco IOS IP SLA Operations  Use the ip sla operation-number global configuration command to begin configuring a Cisco IOS IP SLA operation and to enter IP SLA configuration mode.  The operation-number is the identification number of the IP SLA operation to be configured.

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IP SLA Configuration Mode Commands

 The focus of this section is on the icmp-echo command  The complete command syntax is: • icmp-echo {destination-ip-address | destination-hostname} [sourceip {ip-address | hostname} | source-interface interface-name]. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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IP SLA ICMP Echo Configuration Mode Commands

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Schedule the IP SLA Operation  Once a Cisco IP SLA operation is configured, it needs to be scheduled using the ip sla schedule global configuration command.

 The complete command syntax is • ip sla schedule operation-number [life {forever | seconds}] [starttime {hh:mm [:ss] [month day | day month] | pending | now | after hh:mm:ss}] [ageout seconds] [recurring]

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Step 2: Configuring Cisco IOS IP SLA Tracking Objects  Use the global configuration command: • track object-number ip sla operation-number {state | reachability}

 Use this optional command to specify the period of time to delay communicating states changes: • delay {up seconds [down seconds] | [up seconds] down seconds}

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Step 3: Defining an Action Associated with a Tracking Object  Many types of actions can be associated with a tracked object.  A simple path control action is to use the global configuration command: • ip route prefix mask {ip-address | interface-type interface-number [ipaddress]} [track number]

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Configuring IP SLA Example

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Configuring an IP SLA Operation with the ISP 1 DNS Server

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Defining a Tracking Object and Assigning an Action

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Configuring an IP SLA Operation with the ISP 2 DNS Server

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Configuring an IP SLA Operation with the ISP 2 DNS Server

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Configuring PBR and IP SLA Example

-Web traffic to the HQ site should be redirected over the serial link. -All other traffic from Notebook should go via BR2 but only if BR2 is reachable. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Redirecting Web Traffic from BR1 to HQ Using PBR

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Redirecting Web Traffic from BR1 to HQ Using PBR

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Ensuring That BR2 Is Reachable Using IP SLA

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Redirect Traffic from Notebook to BR2 If Reachable

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Verifications

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Verifications

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Verifications

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Summary

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Summary  Packet-switching mechanisms on a Cisco IOS platform, including process switching, fast switching, and CEF switching.  Overview of path control tools, including PBR and Cisco IOS IP SLAs.  Using PBR to control path selection, providing benefits including source-based transit provider selection, QoS, cost savings, and load sharing.  PBR is applied to incoming packets; enabling PBR causes the router to evaluate all packets incoming on the interface using a route map configured for that purpose. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Summary  Configuring and verifying PBR, including the following steps: • Choose the path control tool to use; for PBR, route-map commands are used • Implement the traffic-matching configuration, specifying which traffic will be manipulated; match commands are used within route maps • Define the action for the matched traffic, using set commands within route maps • Apply the route map to incoming traffic or to traffic locally generated on the router • Verify path control results, using show commands

 Cisco IOS IP SLAs, which use active traffic monitoring, generating traffic in a continuous, reliable, and predictable manner, to measure network performance. Chapter 5 © 2007 – 2010, Cisco Systems, Inc. All rights reserved.

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Summary  Cisco IOS IP SLA terminology, including the following: • All the Cisco IOS IP SLA measurement probe operations are configured on the IP SLA source. • There are two types of IP SLA operations: those in which the target device is running the IP SLA responder component. • An IP SLA operation is a measurement that includes protocol, frequency, traps, and thresholds.

 Configuring and verifying IOS IP SLAs.

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