Cisco IOS IP SLA is a network performance and diagnostic utility that uses real time monitoring to check the health of an IP enabled device. This involves the generation of traffic in a reliable and predictable way.
Simple ICMP Monitoring
The routers could be geographically far apart or relatively near one another, but I want to utilise IP SLA to continuously monitor the f0/0 link on R2 from R1. Perhaps for failover purposes or the interface is getting over utilised and we want to see if this is leading to dropped packets, and we don’t have any other monitoring tools.
The configuration for your basic ICMP IP SLA is really easy as we’re only sending ICMP packets, so we don’t need to configure the destination host with a responder – we’ll get to that with another post – think VoIP!
Note IOS version used – C3725-ADVENTERPRISEK9-M, Version 12.4(25d)
Configure R1’s f0/0 interface with the following:
Once this config has taken we can run some commands to see the information we’re receiving.
Those I find most useful:
show ip sla monitor operational-state 1
- Entry number – The number we configured for our ICMP IP SLA
- Operations attempted – How many ICMP packets have been attempted to be sent
- Operational state of entry – Is our IP SLA working or not
- Latest RTT – How long in milliseconds did the last IP SLA test Round Trip Time take
- Latest operation return code – Did the latest test return ok – yes!
show ip sla monitor statistics 1
- Number of successes – How many packets have been sent in total
- Number of failures – How many packets have failed in tot
As you can see, there’s quite a lot of good information, even with just a simple ICMP IP SLA configured.
As well as ICMP you can also configure tests such as DNS, Specific UDP + ports, TCP + ports, HTTP (really cool) and a really important one if you’re looking to roll out VoIP – UDP Jitter!