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F5User211_37693's avatar
F5User211_37693
Icon for Nimbostratus rankNimbostratus
Nov 14, 2018

DNS load balancing between ISP's

Hello everybody!

 

I have a question about how to approach a problem that we are facing...

 

We have two different ISP's (without BGP - not possible here). Currently, we are using the DNS Made Easy function of failovering our outside DNS's between IP's on both ISP's when one link is down - but it is very unreliant and a lot of times it wrongly recognises a down link. So we would like to transfer the functionality to our F5 with (F5 DNS)...

 

How to approach this issue and does anybody have any experience/guides regarding solutions like this?

 

Thank you and best regards!

 

application delivery
BIG-IP DNS
LTM

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  • Philip_Jonsson's avatar
    Philip_Jonsson
    Icon for MVP rankMVP
    Nov 14, 2018

    Hey!

     

    Since the BIG-IP DNS GSLB function works on an Wide IP basis, I'd say it'd be best to move each DNS record at a time, creating a Wide IP for each FQDN. Then create two pools, one for ISP1 IP address and one for ISP2 IP address.

     

    If you want one ISP to be the primary, you can use the Global Availability load balancing algorithm. That way the pool highest in the list will primarily receive traffic. But if that pool goes down, the secondary will be the one being sent back in the DNS response.

     

    You can read more about GSLB here:

     

    Manual Chapter: About Global Server Load Balancing

     

    I hope this helps!

     

    Let me know if you have any further questions :)

     

  • F5User211_37693's avatar
    F5User211_37693
    Icon for Nimbostratus rankNimbostratus
    Mar 25, 2019

    Hello Philip!

     

    Your answer helped me a lot in designing the solution. And now is the part of the implementation... And I still have one thing that is not completely clear to me... How can I monitor the ISP's? Can I setup transparent icmp_gateway monitors that ping 8.8.8.8 and set them up per pool? But it doesn't seem to work.

     

    If I do it your way (monitor the services as you wrote) I can never be sure if the ISP is really UP? Note the VIP's are setup in my LTM (I do have LTM...)

     

    So a basic topology of mine is:

     

    router (connected with 2 ISP's) - F5 (GTM/LTM/ASM) - FW - Servers

     

    Thank you for your help! And I loved both your books, they helped me to my cert :)