The above configuration defines and starts an IP SLA probe. The above commands are for IOS 12.4(4)T, 15.(0)1M, and later releases. Please note that the Cisco IP SLA commands have changed from IOS to IOS to know the exact command for IOS check the Cisco documentation. R1(config)# ip sla schedule 1 life forever start-time now R1(config)# icmp-echo 2.2.2.2 source-interface FastEthernet0/0 Following a sample configuration of IP SLA to generate icmp ping targeted at the ISP1s next-hop IP. The pings are routed from the primary interface only. IP SLA is configured to ping a target, such as a publicly routable IP address or a target inside the corporate network or your next-hop IP on the ISP's router. The Reliable Static Routing Backup using Object Tracking feature can ensure reliable backup in the case of several catastrophic events, such as Internet circuit failure or peer device failure. Using IP SLA the Cisco IOS gets the ability to use Internet Control Message Protocol (ICMP) pings to identify when a WAN link goes down at the remote end and hence allows the initiation of a backup connection from an alternative port. With around six additional IOS commands we can have a more reliable automatic failover environment. In such scenarios, IP SLAs becomes an engineer's best friend. But in a lot of situations we see that even though the links remain up but we are not able to reach the gateway, this usually happens when the issue is at the ISP side. The above configuration with just two floating static routes partially accomplishes our requirement as it will work only in the scenario where the routers interfaces connected to the WAN link are in up/down or down/down status. If you notice the Administrative Distance for the secondary route pointing to ISP2 is increased to 10 so that it becomes the backup link. The most common setup that we use in day to day life is to have to default routes configured on the Cisco router pointing to the respective next hop IPs as shown below: In the above figure the Cisco device is connected to two WAN links ISP1 and ISP2. Let us take an example of a basic redundant WAN link scenario as shown below:
Users interested can head to our Cisco Routers section where they can find a number of articles covering IP SLA configuration on Cisco routers. IP SLA in itself is a very big topic to cover. The number and type of available measurements are vast and in this article we will be covering just the ICMP ECHO feature.
With IP SLAs, routers and switches perform periodic measurements. Cisco Routers provide IP SLA Responders that give accuracy of measured data across a network. This is a reliable method in measuring over head network performance. IP SLA's uses active traffic-monitoring technology to monitor continuous traffic on the network.
UROUTE TRACKING SOFTWARE
IP SLAs is a feature included in the Cisco IOS Software that can allow administrators the ability to Analyze IP Service Levels for IP applications and services. The best and simplest way to achieve WAN redundancy on Cisco devices is to use Reliable Static backup routes with IP SLA tracking. In this topic we will be covering WAN redundancy with multiple WAN links terminating on a single router. In today's network environment, redundancy is one of the most important aspects, whether its on the LAN side or on the WAN side.
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