Cisco 300-540 Exam - Topic 4 Question 2 Discussion

On R1 the configuration (simplified) is:

ip domain lookup

ip domain name ccnp.test

ip host www.ccnp.test 10.1.1.1 10.2.1.1 10.3.1.1

The ip host command statically maps the hostname www.ccnp.test

to three IP addresses. By default, Cisco IOS will always return these IP addresses to DNS queries in the same order they are configured (10.1.1.1, then 10.2.1.1, then 10.3.1.1). This means that clients will always attempt 10.1.1.1 first and will not achieve per-query load balancing across all three servers.

To enable DNS-based load balancing so that each successive query rotates the order of the addresses, Cisco IOS provides the command:

ip domain round-robin

This command enables round-robin rotation of multiple A records associated with a single hostname defined by ip host. With this feature enabled:

1st query: response order 10.1.1.1, 10.2.1.1, 10.3.1.1

2nd query: response order 10.2.1.1, 10.3.1.1, 10.1.1.1

3rd query: response order 10.3.1.1, 10.1.1.1, 10.2.1.1

Clients will typically try the first IP address in the list and use the others if the first one fails, exactly matching the requirement.

Why other options are incorrect:

A . ip domain retry 3 controls how many times the router retries DNS queries to a server; it does not control the order of multiple A records.

C . ip dns server turns the router into a DNS server but does not itself provide round-robin behavior for statically defined hosts.

D . maximum-paths 3 is a routing (IP forwarding) parameter for equal-cost multipath, unrelated to DNS resolution.