IP subnet check
Prerequisites:
None
Package:
Availability.
Executed on:
In-check execution.
Check interval:
Every 4 hours.
Impact on Availability:
None.
Impact on Integrity:
None.
Purpose
Informational/indicational only.
When building a DNS infrastructure it is good practice not to place the DNS servers on the same subnet. It is also preferable to have them connected through different network hardware as well, to avoid losing multiple DNS servers on a single switch or firewall failure.
This check is using /24 for IPv4 and /64 for IPv6 as the smallest subnets. For IPv4 in particular, there is a distinct possibility that sub-24 networks are used, why this check is merely used as information.
On the other hand, should the same subnet be used for multiple DNS servers this check is a good indication that the current DNS infrastructure has some serious design issues.
Event severities and messages
INFO
All name servers appear to be located on different subnets.
To have the DNS infrastructure split between at least two different subnets makes it less vulnerable to network and hardware failures.
WARNING
Some name servers appear to be located on the same subnets.
This may be a design flaw. It is never a good idea to have multiple DNS servers on the same physical network. Note that the check only uses /24 and /64 as subnet reference.
Solutions, tips & tricks
If possible, separate DNS servers between different network segments and physical hardware to avoid unnecessary outages from a single hardware failure.