IPSLA


In today’s networks redundancy is one of the most important and crucial aspects.
IPSLA is one of the great tools we can you to achieve this.
IP SLA is a very big topic to cover and today I’d like to show you a small section of it where we are going to use ICMP ping for as an active traffic-monitoring technology to monitor continuous traffic on the network.

IPSLA

Take a look at the above topology.We have R1 connected to two WAN links R2-ISP1 and R3-ISP2. The most common setup that we use in day to day life is to have to default routes configured pointing to the respective next hop IPs as shown below

R1(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.2
R1(config)# ip route 0.0.0.0 0.0.0.0 172.16.1.3 10

The above configuration with a floating static (different admin distance in the second static statement where we have set it to the value of 10) routes does not fully accomplishes our requirement as it will work only if the routers interfaces connected to the WAN links are in up/down or down/down status. 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.

There are two different methods to configure IPSLA depending on the IOS version that you’re running so watch out for both.

ip sla monitor 1
type echo protocol ipIcmpEcho 192.168.1.2 source-interface FastEthernet0/1
ip sla monitor schedule 1 life forever start-time now
track 1 rtr 1 reachability

OR

ip sla 1 
icmp-echo 192.168.1.2 source-interface FastEthernet0/1
ip sla schedule 1 life forever start-time now
track 1 ip sla 1 reachability

This is the simplest configuration that we need in order to make it work and of course we can add many other options such as:

R1(config)# timeout 1000
R1(config)# threshold 2
R1(config)# frequency 3

The ICMP Echo probe sends an ICMP Echo packet to next-hop IP 192.168.1.2 every 3 seconds, as defined by the “frequency” parameter.

Timeout sets the amount of time (in milliseconds) for which the Cisco IOS IP SLAs operation waits for a response from its request packet.

Threshold sets the rising threshold that generates a reaction event and stores history information for the Cisco IOS IP SLAs operation

Both above IPSLA configs accomplish the same thing, last thing that we need to do is to start tracking

R1(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.2 track 1
R1(config)# ip route 0.0.0.0 0.0.0.0 172.16.1.3 10

 

Enjoy !
Tom

 

 

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About ccie4all
Hello, and welcome to the first post of my CCIE blog This blog has got one simple goal and that is to improve our skills in Cisco Networking field so we can become best engineers on a job market. Wordpress Blog https://ccie4all.wordpress.com/ information about the changes made to Gns3 BGP , MPLS and R&S CCIE labs. In order to access and download all provided materials and receive important updates from Gns3 BGP , MPLS and R&S CCIE labs under GNS3 tab in the main header please go ahead and subscribe to https://ccie4all.wordpress.com/ ! All other posts have not been affected and can be accessed at any given time. Enjoy ! Tom

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