IP SLA for DNS trigger problem

[Majed Saeed]

Hi Folks

I'm facing an issue while configuring IP SLA for DNS trigger between two routers connected to each other like R1 <<>> R2 .

R1 - IP 10.1.2.1

R2 - IP 10.1.2.2

Please find below helpful logs .. Looking for your thankful assistance 

-----------------------------

R1 Config.

ip sla 1
 dns 10.1.2.2 name-server 10.1.2.2 source-port 53
 timeout 100
 threshold 500
 frequency 9
ip sla schedule 1 life forever start-time now
!

R1 show ip sla statistics

R1#sh ip sla statistics

Round Trip Time (RTT) for       Index 1
        Latest RTT: NoConnection/Busy/Timeout
Latest operation start time: *00:13:56.363 UTC Fri Mar 1 2002
Latest operation return code: Timeout
Number of successes: 0
Number of failures: 36
Operation time to live: Forever

 R1 debug ip sla err

*Mar  1 00:11:59.371: IP SLAs(1) dns operation: Error code=4
*Mar  1 00:11:59.371: IP SLAs(1) Scheduler: Updating result
*Mar  1 00:11:59.375: IP SLAs(1) Scheduler: start wakeup timer, delay = 8988
R1#
*Mar  1 00:12:08.363: IP SLAs(1) Scheduler: saaSchedulerEventWakeup
*Mar  1 00:12:08.363: IP SLAs(1) Scheduler: Starting an operation
*Mar  1 00:12:08.367: IP SLAs(1) dns operation: Starting dns operation
*Mar  1 00:12:08.367: IP SLAs(1) dns operation: Query addr - 10.1.2.2
*Mar  1 00:12:08.367: IP SLAs(1) dns operation: actual target queried = 2.2.1.10.in-addr.arpa
R1#
*Mar  1 00:12:17.371: IP SLAs(1) dns operation: Error code=4
*Mar  1 00:12:17.371: IP SLAs(1) Scheduler: Updating result
*Mar  1 00:12:17.375: IP SLAs(1) Scheduler: start wakeup timer, delay = 8988

[Terence Payet]

Hello,

You have to configure the other router as a dns server. 

But i dont think it will work. Unless you were querying a working dns server.

But based on the debug output the ip sla source is trying to query the dns server as per the output below:

*Mar  1 00:12:08.367: IP SLAs(1) dns operation: actual target queried = 2.2.1.10.in-addr.arpa

Mar  1 00:12:17.371: IP SLAs(1) dns operation: Error code=4

HTH

Please rate helpful post.

Regards,

Steve

[Majed Saeed]

Hi Steve 

It is already R2 as DNS server 

[Peter Paluch]

Hello,

Why are you trying to resolve the "10.1.2.2" string in DNS? This would actually mean that you want a reverse lookup from an IP address back to a fully qualified domain name, that is, a PTR record. You would need to create a PTR record on the DNS for this purpose. Usually, you should be looking for a normal lookup from a domain name to an IP address, such as "www.google.com" or "www.yourdomain.com".

Best regards,
Peter

[Majed Saeed]

Hi Peter

I just thought that since 10.1.2.2 is R2 interface IP and as long as configured the same as DNS server through CLI . That might make R2 as server for lookup . Could you please elaborate me more how can make this works .

[Peter Paluch]

Hi Majed,

The SLA probe should be configured similarly to this:

ip sla 1
 dns www.google.com name-server 10.1.2.2 source-port 53
 timeout 100
 threshold 500
 frequency 9
ip sla schedule 1 life forever start-time now

Best regards,
Peter