IP SLA with ICMP and TTL

[2044418Puts]

Hi,

I would like to configure a "ip sla" based on ICMP but with a specific TTL. Is this possible?

(Based on IP (not MPLS))

[Ian Wilson]

The following example configures an IP SLA instance to send an ICMP Echo (ping) packet every 3 seconds.

Timeout is set to 1 second, and threshold is set to 2 milliseconds.

If the ICMP reply is received within 1 second (timeout value) then the IP SLA 'operation return code' is 'OK'.

If the reply is received between 2 millisecs and 1 second then OverThreshold is set.

ip sla 1

type echo protocol ipIcmpEcho 10.51.12.4 <<< Ping operation

timeout 1000 <<< Timeout in 1 sec

frequency 3 <<< Ping every 3 secs

threshold 2 <<< 2 mS threshold

request-data-size 1400

ip sla sched 1 start-time now life forever <<< Shedule operation to start now and run forever

!

Ian

[2044418Puts]

Thanks for your reply, but I would like to verify reachability with a specific TTL (hop count). For example:

The tracker should return OK only if the host to ping is only 2 hops away, but not if it is 3 hops away. For example due to a change in one of the intermediate router's routing table.

Please let me know if this is possible. Thanks

[akharmanbiz]

Hi,

I think no solution for ttl in ip sla monitor or if exist you must upgarde your IOS image.

[Florin Barhala]

Hello,

Any new idea regarding this request? I need to monitor a connection but I have to be sure the reply comes from ONE hop distance.

I require this because the ping_server_for_ISP1  I use is reachable using both ISP and I cannot know when ISP 1 is down (I originate icmp packets from ISP1_connected_interface). Here is the config if helps anyway:

ip sla monitor 10

type echo protocol ipIcmpEcho 193.aa.bb.201 source-ipaddr 89.xx.yy.18

timeout 1000

frequency 4

ip sla monitor schedule 10 life forever start-time now

track 10 rtr 10 reachability

delay down 10 up 30

ip route 0.0.0.0 0.0.0.0 89.238.226.17 track 10

[cadet alain]

Hi,

if you want to get sure the IP SLA probe is sent to first ISP then either use:

- source-interface in your IP SLA config

- configure a static host route for the destination you are probing

- configure a local PBR policy to always send the SLA probes out the interface to first ISP

I've never heard about an option for setting  TTL of ICMP echo-request for IP SLA.

Regards.

Alain

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[Florin Barhala]

Hi Alain,

I configured IP SLA using "source-interface in your IP SLA config"; but here it is:

- ISP1_ping_server goes down and primary default route is removed from routing table

- then ISP2_default route comes in place and then ISP1_ping_server is reachable using ISP2 connection. This triggers

primary default route to get up and so on...

Any ideas?

I use IOS Version 12.4(25b).

[cadet alain]

Hi,

Try of of the other 2 workarounds I proposed and tell me.

Regards.

Alain

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[Florin Barhala]

Hi Alain,

2nd path sends me to the same result, as the static route uses 1st ISP; but when it fails the ISP1_ping_server will be reached using the DEFAULT route from the 2nd ISP.

I believe it shouldn't behave this way as long as I use the source_interface option in the ip sla configuration, nevertheless I will dig more on this issue.

[cadet alain]

Hi,

no it shouldn't behave this way but having the full config could maybe help us to troubleshoot this.

Regards.

Alain

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