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This product reached the end of support date on March 31, 2021.

Hostname and IP mapping in DCRUM



We are monitoring Desktop traffic where IP's are dynamic based on DHCP. How Dynatrace will mapp Ip and hostname in that case as we are getting wrong data.




DynaMight Pro
DynaMight Pro

DCRUM relies on DNS (either O/S or configured in DCRUM) to resolve host names to IP addresses. All hosts with static or DHCP reserved IP addresses should resolve correctly.
Unfortunately due to the nature of DHCP, there is no guarantee that a device will receive/retain the same IP address forever. The only sure-fire way to get around your problem would be to either create reservations in DHCP or to assign static IP's, both of which defeats the purpose of having a DHCP server in the first place.

However, one can decrease the chances of an IP address change for a device, by increasing the lease time. The DHCP server will only reassign an IP address if the device it was issued to, doesn't try to renew within the allotted timeframe. If the DHCP lease time is set very low, you'll increase the chances of a device receiving a different IP address than it had previously, if said device is offline for more than the configured lease time or part thereof.

I hope I'm making sense, I'm struggling to put what's in my mind, into text 😉

Thanks but in case of DHCP IP's, how and when DCRUM will change the hostname/ip mapping ?

Dynatrace Pro
Dynatrace Pro

The DNS resolver in DC RUM, caches results for 7 days, any changes within that period won't be seen.

If your DHCP lease time is less than that you'll very likely run into names being out of date for clients. Even if the lease time is 7 days or longer, it's still possible for there to be periods of time between when a lease changes and when DC RUM does a new DNS lookup to get the new name.

You can reduce the cache time DC RUM uses, the side affect here is the extra load it'll place on your DNS infrastructure - lots more queries. This may or may not be a problem.

Hi Chris,

Thanks but in our environment there are cases where client IP is not changed where it assigned to Desktop from weeks. Kindly assist.

Where I usually see this, the issue traces to the DNS not reporting the correct name on a reverse look up against the IP address.

-- Erik