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This chapter is from the book

This chapter is from the book

Cisco IOS IP Service Level Agreements

Figure 5-1 shows the network topology for the configuration that follows, which shows the use of Cisco IOS IP SLA functionality for path control.

Figure 5-1

Figure 5-1 Cisco IOS IP Service Level Agreements

Customer requirements:

  • Customer A is multihoming to ISP-1 and ISP-2.
  • The link to ISP-1 is the primary link for all traffic.
  • Customer A is using default routes to the ISPs instead of BGP.
  • Customer A is using static routes with different administrative distances to make ISP-1 the preferred route.

Potential problem: If ISP-1 is having uplink connectivity problems to the Internet, Customer A will still be sending all of its traffic to ISP-1, only to have that traffic lost.

Solution: IOS IP SLA will be used to announce conditionally the default route to ensure reachability of a specific destination.

Follow these steps to configure Cisco IOS IP SLA functionality:

  • Step 1. Define one (or more) probes.
  • Step 2. Define one (or more) tracking objects.
  • Step 3. Define the action on the tracking object(s).
  • Step 4. Verify IP SLA operations.

Step 1: Define One (or More) Probes

R1(config)#ip sla monitor 22
               

Begins configuration for an IP SLA operation and enters SLA monitor configuration mode. 22 is the operation number and is a number between 1–2147483647.

R1(config-sla-monitor)#type echo protocol ipIcmpEcho 10.1.1.1 source-interface fastethernet 0/0
               

Defines an ICMP Echo operation to destination address 10.1.1.1 through source interface of FastEthernet 0/0 and enters ICMP Echo configuration mode.

R1(config-sla-monitor-echo)#frequency 10
               

Sets the rate at which the operation repeats. Measured in seconds from 1–604800 (7 days).

R1(config-sla-monitor-echo)#exit
               

Exits IP SLA Monitor ICMP Echo configuration mode and returns to global configuration mode.

R1(config)#ip sla monitor schedule 22 life forever start-time now
               

Sets a schedule for IP SLA monitor 22. Packets will be sent out immediately and will continue forever.

Step 2: Define One (or More) Tracking Objects

R1(config)#track 1 sla 22 reachability

Configures the tracking process to track the reachability of IP SLAs operation 22.

Step 3: Define the Action on the Tracking Object(s)

R1(config)#ip route 0.0.0.0 0.0.0.0 11.1.1.1 3 track 1

Announces a default route to 11.1.1.1 with an administrative distance of 3 if the tracking object 1 is true.

Step 4: Verify IP SLA Operations

R1#show ip sla configuration

Displays SLA components such as frequency, target address, scheduling, and other parameters.

R1#show ip sla statistics 22

Displays number of successful and failed probes, last operation, start time, and last return code for SLA monitor 22.

R1#show ip sla statistics 22 detail

Displays more in-depth output for SLA monitor 22.

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