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IP SLA with ICMP and TTL

2044418Puts
Level 1
Level 1

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))

9 Replies 9

Ian Wilson
Level 1
Level 1

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

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
Level 1
Level 1

Hi,

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

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

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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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).

Hi,

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

Regards.

Alain

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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.

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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