why is the router sending reverse DNS queries ?

[SJ K]

Hi all,

While doing a trace for a traceroute command, i realize that the router is actually doing a reverse DNS query for the ip that I am doing the traceroute.

Although this does not impact my traceroute, I can't help to wonder why the need to do the reverse DNS for ?

1    0.000000000    192.168.5.1    255.255.255.255    DNS    84    Standard query 0x2f3e  PTR 2.5.168.192.in-addr.arpa

3    5.750328000    192.168.5.1    255.255.255.255    DNS    84    Standard query 0x2f3e  PTR 2.5.168.192.in-addr.arpa

5    10.828742000    192.168.5.1    192.168.5.2    UDP    60    Source port: 49246  Destination port: 33435

6    10.859994000    192.168.5.2    192.168.5.1    ICMP    70    Destination unreachable (Port unreachable)

Regards,

Noob

[Jon Marshall · Accepted solution]

It's the default behaviour of traceroute and it is doing it to try and display a hostname rather than an IP address.

If you want to stop it doing that then use the "numeric" option with the traceroute command.

Whenever I am testing in a lab I always use that option because doing the reverse lookup significantly slows down the traceroute if there is no DNS server to respond.

Jon

[SJ K]

Hi Jon,

Duly noted. I realize after you reply, this thread is gone.  I am wondering did you see my previous questions in the forum that i raised today ;(.

Regards,

Noob

[Jon Marshall]

Yes I have dropped a line to the support team about this.

I have responded to two separate posts and both have gone from the forum.

So it's not just your posts.

I have no idea what is going on at the moment.

Jon

[SJ K]

Hi Jon,

Thanks. I hope you really dont mind me asking - to assist to take a look at these 2 related threads below (as i spend an entire day doing testing and researching but to no avail)... ;(

Hope you are able to shed some light ;(

https://supportforums.cisco.com/discussion/12492246/pinging-remote-broadcast-address-cant-understand-response

https://supportforums.cisco.com/discussion/12490926/ping-no-response-found-what-does-it-meant

Thank you

[SJ K]

Hi Jon,

Thanks. I hope you really dont mind me asking - to assist to take a look at these 2 related threads below (as i spend an entire day doing testing and researching but to no avail)... ;(

Hope you are able to shed some light ;(

https://supportforums.cisco.com/discussion/12492246/pinging-remote-broadcast-address-cant-understand-response

https://supportforums.cisco.com/discussion/12490926/ping-no-response-found-what-does-it-meant

Thank you

[SJ K]

Hi Jon,

Duly noted. I realize after you reply, this thread is gone.  I am wondering did you see my previous questions in the forum that i raised today ;(.

Regards,

Noob

[SJ K]

Hi Jon,

Duly noted. I realize after you reply, this thread is gone.  I am wondering did you see my previous questions in the forum that i raised today ;(.

Regards,

Noob