Can I have Inbound load balancing achieved with below settings

Joseph S D Yao jsdy at tux.org
Wed Nov 13 13:25:59 UTC 2013


On 2013-11-13 00:16, Manish Rane wrote:
...
> 6.Assume if ISP1 goes down, client coming on ISP1 would never be able
> to reach; hence as per DNS protocol will try for another link and 
> come
> on ISP2 and then probably get an IP address of Link 2 i.e. 2.2.2.2.
...


I'm not sure about your DNS setup, because I didn't understand how you 
described it.  But that doesn't matter.

Even if you 100% properly did what you intended to do, it breaks down 
at step 6.  The DNS protocol definitions only go as far as saying what 
your BIND DNS server will return.  Importantly (for this answer), it 
does NOT say (a) what a remote user's caching/resolving name server will 
actually do with your responses, or (b) what the actual application will 
do with your responses.

If the application is an SMTP server or another DNS server then, yes, 
BY THE DEFINITION OF THAT PROTOCOL, it will try again for another 
server.

If the application is a Web browser - which is likely, given that you 
mention port 80, presumably TCP - then it will only look at one of the 
two IP addresses [for almost all currently available Web browsers].  If 
it gets a bad one, it will return the user an error.  Because that is 
how THAT protocol is defined.  Most protocols are not defined to re-try 
different servers.

What you are trying to do is what the F5 BigIP GTM does - only return 
the IP address for a known-working site.  There's a reason that F5 can 
sell those boxes - they work where doing this in pure DNS does not.


Joe Yao


More information about the bind-users mailing list