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dhcpd dns Config on ASA

Answered Question
Aug 14th, 2013
User Badges:

Hi Everyone,


On my ASA  i do not have the config

dhcpd dns 64.59.144.19


this is my ISP DNS.

Without the command i am still able to access the internet and ASA  log shows


Aug 14 2013 19:31:09: %ASA-6-302016: Teardown UDP connection 1481 for outside:64.59.144.19/53 to DMZ:192.168.70.2/60527 duration 0:00:00 bytes 90

Aug 14 2013 19:31:09: %ASA-6-302016: Teardown UDP connection 1480 for outside:64.59.144.19/53 to DMZ:192.168.70.2/53809 duration 0:00:00 bytes 390


Is this default behaviour?


Regards


MAhesh


Message was edited by: mahesh parmar

Correct Answer by Julio Carvajal about 4 years 5 days ago

Hello Mahesh,


with the capture we will not be able to look for something useful as the client already has the DNS server.


What would be good is to check on the client side any configuration related to DNS on the LAN or WLAN properties.


We can see that they are using 64.59.144.19 as the DNS server but the question is how the get it, not from the ASA.... the Switch with only that configuration will not be the one...


There got to be some other clue that you could provide us


7          2.650999          192.168.70.3          64.59.144.19          DNS          73          Standard query A www.google.ca


Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

Correct Answer by Julio Carvajal about 4 years 6 days ago

Hello,


I mean the switch is aware of the DNS servers but based on the configuration you provided there are no sufficient inputs to determine whether it's broadcasting the DNS IP addresses.


So on the client side or any other Active Directory setting there is no DNS configuration setting?


Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

Correct Answer by Jouni Forss about 4 years 6 days ago

Hi Mahesh,


Are you perhaps using DHCP also on the ASAs "outside" interface?


Do you have this configured perhaps?


dhcpd auto_config outside


You can view this with command


show run dhcpd


- Jouni

Correct Answer by Julio Carvajal about 4 years 6 days ago

Hello,


If you do not have provided to them the DNS server via DHCP how are they using the protocol?


They might have it statically configured or other device is providing that service, do a capture on the client side with wireshark and check where they get the DNS address from.?


Can you doble check that,



Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

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Correct Answer
Julio Carvajal Wed, 08/14/2013 - 20:47
User Badges:
  • Purple, 4500 points or more

Hello,


If you do not have provided to them the DNS server via DHCP how are they using the protocol?


They might have it statically configured or other device is providing that service, do a capture on the client side with wireshark and check where they get the DNS address from.?


Can you doble check that,



Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

Correct Answer
Jouni Forss Wed, 08/14/2013 - 20:51
User Badges:
  • Super Bronze, 10000 points or more

Hi Mahesh,


Are you perhaps using DHCP also on the ASAs "outside" interface?


Do you have this configured perhaps?


dhcpd auto_config outside


You can view this with command


show run dhcpd


- Jouni

mahesh18 Wed, 08/14/2013 - 21:51
User Badges:

Hi Jouni,


Here is info


ciscoasa#                                 sh run dhcpd

dhcpd address 192.168.70.2-192.168.70.254 DMZ

dhcpd enable DMZ

!

dhcpd address 10.0.0.2-10.0.0.100 inside

dhcpd enable inside



Seems  the switch connected to ASA  is providing the DNS


3550SMIA# sh run | inc dns

   dns-server 64.59.144.19

   dns-server 64.59.144.19

   dns-server 64.59.144.19



This switch is directly connected to ASA outside interface.


ASA outside interface has static ip.


interface Vlan1

description Connection to Outside 3550A

nameif outside

security-level 0

ip address 192.168.71.2 255.255.255.0



So in this scenario switch is provding the dns?


Regards


Mahesh

Correct Answer
Julio Carvajal Wed, 08/14/2013 - 22:20
User Badges:
  • Purple, 4500 points or more

Hello,


I mean the switch is aware of the DNS servers but based on the configuration you provided there are no sufficient inputs to determine whether it's broadcasting the DNS IP addresses.


So on the client side or any other Active Directory setting there is no DNS configuration setting?


Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

mahesh18 Thu, 08/15/2013 - 17:52
User Badges:

Hi Julio,


I have attached the wireshark capture under the original post.

now is cap file.


Can you have a your expert  look


Regards


Mahesh

Correct Answer
Julio Carvajal Thu, 08/15/2013 - 18:16
User Badges:
  • Purple, 4500 points or more

Hello Mahesh,


with the capture we will not be able to look for something useful as the client already has the DNS server.


What would be good is to check on the client side any configuration related to DNS on the LAN or WLAN properties.


We can see that they are using 64.59.144.19 as the DNS server but the question is how the get it, not from the ASA.... the Switch with only that configuration will not be the one...


There got to be some other clue that you could provide us


7          2.650999          192.168.70.3          64.59.144.19          DNS          73          Standard query A www.google.ca


Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

mahesh18 Thu, 08/15/2013 - 18:37
User Badges:

Hi Julio,


You are the best i checked the TCP properties the DNS  was hard coded there instead of obtain it automatically.


Best regards


MAhesh

Julio Carvajal Thu, 08/15/2013 - 20:15
User Badges:
  • Purple, 4500 points or more

Hello Mahesh,


Thanks for the kind words, I really appreciate them,


Glad to know that I could help,


Check my blog at http:laguiadelnetworking.com for further information.

Cheers,

Julio Carvajal Segura

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