You have an Exchange Server 2013 organization that contains two Client Access servers and two Mailbox
servers.
You configure DNS round robin on the Client Access servers. All of the host (A) and alias (CNAME) records in
the DNS zone are configured to have a TTL value of 10 minutes.
You need to recommend a solution to fail over client connections to a Client Access server automatically if
Internet Information Services (US) fails. The solution must minimize costs.
What should you recommend?
A.
Deploy a Client Access server array.
B.
Reduce the TTL values on all of the A and CNAME records to one minute.
C.
Deploy a hardware load balancing solution.
D.
Deploy Network Load Balancing (NLB) on each Client Access server.
Explanation:
NLB will not suffice in this scenario as it is not service aware. If IIS fails, or one of the IIS components fail,
WLNB will not detect there is an issue with the CAS server.
http://www.stevieg.org/2010/11/exchange-team-no-longer-recommend-windows-nlb-for-client-accessserverload-balancing/
“What we [Microsoft] recommend is a hardware load balancer for most deployments.. there are several
reasons..Hardware load balancers provide you service awareness, so you can actually get down to the individual, not
only the individual TCP port, TCP 443 as an example, but you can potentially get down to the individual
application as part of that service, depending on the load balancer you deploy. So now you can know if the web
service, or the EWS service I should say, is failed – but OWA is still functioning on the CAS array. And you
could take that member out of service as the result of that one failure because maybe you have.. Lync deployed
and you rely heavily on the EWS service. “Why not Windows Network Load Balancing? Well – there’s several
issues with it.
One – it only provides the ability to do IP-based affinity. So we don’t get the persistent capabilities that we need.
Two – it doesn’t provide service awareness… it’s “server-aware”. If the web service fails, Windows Network
Load Balancing has no concept of that. It just continues to route requests to that and then the user has a
broken experience.