Troubleshoot DHCP and DNS Issues.
Well first, let's take a look at DHCP.
Now I had mentioned that on the exam, AZ‑801, these troubleshooting steps
assume that you're doing DHCP locally. And that's true because the Azure
wire server is responsible for DHCP on your virtual networks. Some tips
that come directly from Microsoft include, number one, verifying that your
DHCP server has been properly authorized to function in your Active
Directory domain.
Kind of embarrassing if this isn't true, but make sure that the DHCP
server service is started. Also make sure that your scopes on the DHCP
server are activated. In a routed environment,
make sure that your routers are supporting DHCP relay or BOOTP forwarding.
This allows DHCP broadcast traffic that typically is using UDP
ports 67 and 68 to go through those interfaces.
So this would allow a DHCP server on VLAN A to service
machines that are on VLANs A, B, and C.
From a client perspective, if a client comes up with an APIPA address,
APIPA, of course, stands for Automatic Private IP
Addressing, the range is 169.254.0.0/16.
This is a very clear indicator that that client was unable to
obtain a lease from a DHCP server, and that's useful information
to know. Lastly, on the DHCP server,
you'll want to look in both the system log, as well as the
DHCP Server service log. Many of you know,
Markman Minasi. He's retired now, but for the early part of my career,
at least half of my career,
he was the guru with Windows Server, and he would
have various mantra expressions.
One of them is it's always DNS. Whatever your problem is,
it's going to affect DNS in some way or another.
And I would agree with that. Here,
I want to give you six examples of compiled executable and
PowerShell commands that can be useful for troubleshooting
DNS server and DNS client.
We have good old nslookup that allows you to query to see what
your client is using as its name server, or you could tap into
the zone file of any reachable DNS server and verify resource
records. On the PowerShell side,
I really love Resolve‑DNSName. When I discovered this command,
which embarrassingly wasn't all that long ago,
I thought, wow, where have you been all my life?
It's such a useful command. Test‑DNSServer reminds me a bit of the old DCDiag.
It's a multi‑use tool to run verification checks against a Windows
Server‑based DNS server. Clear‑DnsClientCache is similar to ipconfig
/flushdns. It's just in many ways a wrapper for that.
We can always use ipconfig, and I do just about every day. And then lastly, we
can look at our interfaces and review their client settings.
So, as you see here, we have a healthy mix of client and server‑side command‑line tools for troubleshooting purposes.