Wrong Values with Ip Sla Path Echo Paths

Document ID : KB000050465
Last Modified Date : 14/02/2018
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Description:

Incorrect successful attempts values with Cisco IP-SLA Path Echo paths

Problem Ticket: PRD00055888

Solution:

If you create hundreds of Cisco SSA (IP SLA) ICMP Path echo tests (probes) on the router they can start seeing Bad Polls in eHealth and ICMP timeout messages in messages.stats.log file. This is caused by the fact that ICMP Path echo test traces each hop on the way from the router to destination and thus issues many ICMP ping requests for each IP SLA dedicated test. Also lots of router resources are consumed to keep the data.

If you do not need to test each hop and keep information about every hop on the route between the router and destination, you can create "ICMP echo" tests instead of "ICMP Path echo" and this will increase router reliability and fix Bad Polls and ICMP timeouts.

The difference between ICMP Echo Path and ICMP echo is following:

---------------------------------- ICMP echo -------------------------------------------

The IP SLAs UDP echo operation measures end-to-end response time between a Cisco router and devices using IP. UDP is a network layer (Layer 3) Internet protocol that is used for many IP services. UDP echo is used to measure response times and test end-to-end connectivity.

UDP echo accuracy is enhanced by using the IP SLAs Responder at Router A, the destination Cisco router. If the destination router is a Cisco router, then IP SLAs sends a UDP datagram to any port number that you specified. Using the IP SLAs Responder is OPTIONAL for a UDP echo operation when using Cisco devices.

A UDP echo operation measures round-trip delay times and tests connectivity to Cisco and non-Cisco devices.

---------------------------------- ICMP Path echo -------------------------------------------

The IP SLAs ICMP Path Echo operation records statistics for each hop along the path that the IP SLAs operation takes to reach its destination. The ICMP Path Echo operation determines this hop-by-hop response time between a Cisco router and any IP device on the network by discovering the path using the traceroute facility.

The source IP SLAs device uses traceroute to discover the path to the destination IP device.

A ping is then used to measure the response time between the source IP SLAs device and each subsequent hop in the path to the destination IP device. This operation does NOT require the IP SLAs Responder to be enabled.

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