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fosiul01Flag for United Kingdom of Great Britain and Northern Ireland

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Related question : Dns server querly is slow

Ref : https://www.experts-exchange.com/questions/25849255/Dns-query-is-slow.html

Hi
Please have a look at network diagram

2 isp is going into a load balancer . From load balancer is going to a firewall.

all client pc is getting IP via dhcp server ( windows SBS 2003 server) and dns query is resolving by SBS 2003 Server.

so client IP address :
IP address example 1 :

192.168.1.10
Gateway : 192.168.1.1.
subnet : 255.255.255.0
DHCP Server : 192.168.1.6
Dns : 192.168.1.6 ( this the ip of SBS Server)
Win :192.168.1.6

Now problem is :

if i turned on both isp line , i can browse properly
but if i turned off isp1 , i can browse via isp2, but its tooo slow

but if i turned of isp2, but keep on isp1, its fine, i can browse fast.

so some how, there is a problem between my SBS Server and isp2, but dont understand what ...


extra note :

now if i hard coded isp2 dns servcer like this
Ip address example 2 :

192.168.1.10
Gateway : 192.168.1.1
subnet : 255.255.255.0
Dns : 10.0.0.12  ( dns server address of isp2)

i can browse fast there is not any problem

but with ip address example 1, browsing via isp2 line is tooo slow

so i am guessing problem could of on dns server on SBS SErver

and i am not a windows guy, so can any one help me to pin point the issue ???

i did not configure this SBS server, so the previous IT guy he used some sort of forwarder aswell...

thanks

also : after putting new ip forwarder, do you have to restart dns server ??
Network-Problem.png
dnsquery.GIF
dnsinterface.GIF
Avatar of Mike Thomas
Mike Thomas
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If each line is with a different isp then set forwarders for both isp's in the forwarders tab, or use forwarders to DNS servers not bound to either ISP, and you do not need to restart the dns service.
Here are some open dns server you could use as forwarders

208.67.222.222 (resolver1.opendns.com)
208.67.220.220 (resolver2.opendns.com)
Avatar of fosiul01

ASKER

Hi
If each line is with a different isp then set forwarders for both isp's  in the forwarders tab  ::
i guess this is how current set up is. . please have a look at both pictures.


if you look at 2nd pic (dnsquery.GIF )

xx.xx.xx.xx and yy.yy.yy.yy is the First isp

zz.zz.zz.zz ( 10.0.0.0.12) is the 2nd isp



what you meant by this

use forwarders to DNS servers not bound to either ISP,

please  have a look top 2 picture from Dns server configuration. and i said, by default All client pc is getting Dns Server IP of 192.168.1.6, which is the SBS server itself ( ref to my comment at question, "ip address example 1" )
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Mike Thomas
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Your main forwarders are to isp1, you kill that link and you are now  connected to isp2, however isp2 won't let you connect to isp1 dns  servers because they are not public, so it ends up using roots hhints  which takes longer to resolve.

this is it, i was thinking this way aswell but in different way

but it could be like this

if you look at 2nd pic , dnsquery.gif...

first 2 ip (xx.xx.xx.xx , yy.yy.yy.yy ) is for isp 1 and zz.zz.zz.zz is for isp 2 and there is 5 sec time [ number of sec before forward query times out ]

so when i kill isp1 link,

all dns query try to go via isp2 and try to do a dns query on isp1 dns server, but isp1 dns server reject those as they are not authoritive .
so 2 ip 5+5 = 10 sec delay

then it try to 3rd ip zz.zz.zz.zz .. its get successful and i am getting webpage after 10 sec which is a big delay

if that true

then my option is not use forwarder

but will it slow down dns query ???

[ i dont want to use open dns servers]


your damm true.

i just put isp2 ip in top then isp1 ip, now when i switch to isp2 line

i can browse properly!!




You can remove all forwarders if you like and just use root hints, but they are not very reliable (hence your  current slow resolution problem)

There is no harm in using public dns servers, maybe just try them for a time and see how it works out?
what i am planning to do is :

we have couple of public vps server. I will make 2 of them as dns server for our organization and will allow those dns server to resolve dns queries only from this 2 ip

hope that should solved the issue

is not it ?? its same as using google dns server but its my own .

Yup same thing and a good idea if you have the servers you can use.
thanks mate
i knew this could be reason but since dont have too much knowledge of windows , i was not 100% sure


thanks anyway

i will  take it from here

thanks
Avatar of arnold
Delete the forwarders should be considered.