Forum Discussion

Narendren_S's avatar
Narendren_S
Icon for Nimbostratus rankNimbostratus
Mar 02, 2014

Issue with GTM loadbalancing for Active-Active sites

Hi,

 

Below is the detail regarding the end users, application requirement, GTM/LTM setup and configuration.

 

Details about end users:

 

  • 80% users are from 3 private LANs located at different sites
  • 20% users are from internet

Number of Sites: 2

 

Application requires persistence

 

Each site is having two 1600 F5 units running as Active-Standby(LTM).

 

And all the 4 units are having GTM module enabled and configured in Active-Active mode.

 

Current Configuration and Issues

 

  • GTM Loadbalancing Method: Topology
  • Persistence: Enabled

Topology Details:

 

  • Private End user LAN Segments are grouped as PRIVATE_LAN - 80% of users
  • IPs not matched PRIVATE_LAN are grouped as PUBLIC - 20% of users

GTM pool is selected based on the end user type

 

  • Both private and public GTM pools are having pool members(LTM VIPs) of both the sites.
  • pool members are having loadbalancing method as round robin.

GTM Loadbalancing Issue

 

In this setup, DNS requests from internet users (PUBLIC) are loadbalanced properly and resolved to both the site LTM VIPs properly, since DNS queries are coming from different ISPs at geographically different location.

 

However, PRIVATE_LAN user DNS queries are originated via very few DNS servers and hence loadbalancing is not happening properly.

 

Note: Consider we have enabled GTM persistence. (as per application requirement)

 

If 1000 requests originated from a private LAN, all those DNS requests resolved to single site LTM VIP since DNS persisted.

 

We require both PUBLIC and PRIVATE_LAN user requests should be loadbalanced to both the GTM sites and persistence should work for the application.

 

It will be great if someone suggest a best solution.

 

BIG-IP DNS

2 Replies

Sort By
  • Narendren_S's avatar
    Narendren_S
    Icon for Nimbostratus rankNimbostratus
    Mar 04, 2014
    Hope some one will help me out to fix this GTM loadbalancing issue for private lan users
  • James_Thomson's avatar
    James_Thomson
    Icon for Employee rankEmployee
    May 08, 2014

    Unfortunately, you have come across the difficult challenge when attempting global load balancing when many people come through very few DNS servers.

     

    The GTM is just a very powerful DNS server, but there's no way around the fact that it is just a DNS server at heart and never sees the client real IP address. If they are willing to put the GTM "in front of" their current DNS servers, then you could deploy the GTM in screening mode which means it will see the client's real IP address on the way to the real DNS servers.

     

    http://support.f5.com/kb/en-us/products/big-ip_gtm/manuals/product/gtm-implementations-11-3-0/2.htmlconceptid

     

    Outside of this solution, there really is no GTM-only solution. You would need to combine GTM with an LTM solution where the LTM looks at the requests as they come in to a virtual server and you redirect them to a site-specific DNS name possibly if they end up at the wrong place.

     

    www.site.com - 1.1.1.1 - 2.2.2.2

     

    w.www.site.com - 1.1.1.1

     

    e.www.site.com - 2.2.2.2

     

    LTM at site A has 1.1.1.1 and LTM at site B has 2.2.2.2. Those virtuals have an iRule that looks at client IP and does another topology lookup. If they are at the wrong site, redirect to other DNS name.