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William_Benett1's avatar
William_Benett1
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Oct 20, 2006

LB based on DNS response?

Hi folks,

 

 

I'm trying to write an iRule to perform a DNS lookup on the IP address of the client, and based on something contained in the reverse, make a load balancing decision.

 

 

Initially I wrote this:

 

 

 

when CLIENT_ACCEPTED {

 

NAME::lookup IP::client_addr

 

}

 

when NAME_RESOLVED {

 

if { [NAME::response] contains ".abc.com"} then {

 

pool www-pool2

 

}

 

}

 

 

But i realize now that, for some reason, I cannot select a pool in the NAME_RESOLVED event.

 

 

Is there a way to pull this off? I'm running on version 9.1.2, but I can upgrade if need be.

 

 

Thanks,

 

--Bill

 

 

I'm testing this rule with HTTP traffic, but in production I need to use this for SMTP and other non-HTTP protocols.
application delivery
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  • William_Benett1's avatar
    William_Benett1
    Icon for Nimbostratus rankNimbostratus
    Oct 20, 2006
    So adding some more data into this. . .

     

     

    It looks like the tmm_config.tcl changes I made were causing the resolve call to go into nowhere. I changed it to point to a hard coded DNS server instead of $IP_ADDR_LOCALHOST. Now I can write an iRule that can successfully log the reverse of the client IP address. I'm guessing that I need named running on the BIG-IP so it can query itself. Just a caveat I suppose, I've moved on from that.

     

     

    I'm now getting a TCL error: Rule DNSbasedLD - Address in use (line 3) invoked from within "pool www-pool2"

     

     

    I still believe that i'm not allowed to make LB decisions in the NAME_RESOLVED event. The only thing I can think of is writing a method, in this iRule, to load balance using the "node" command. That seems really icky. Any advise would be appreciated.
  • William_Benett1's avatar
    William_Benett1
    Icon for Nimbostratus rankNimbostratus
    Oct 24, 2006
    It took me a while, but I figured it out.

     

     

    This code seems to work:

     

     

    when CLIENT_ACCEPTED {

     

    NAME::lookup [IP::client_addr]

     

    }

     

    when NAME_RESOLVED {

     

    if { [NAME::response] contains "abc.com"} then {

     

    LB::detach

     

    pool www-pool2

     

    } else {

     

    LB::detach

     

    pool www-pool1

     

    }

     

    }

     

     

    The key is detaching the LB pool before assigning a new one.