Debugging techniques, problem-solving approaches, and issue resolution
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Any time I have to do anything with OSPF I remind myself how it can be so damn awkward about MTU. A little while ago I was busy trying to integrate some Juniper SRX firewalls into a perimeter around some Cisco Nexus 7K and reached a problem that looked like MTU, smelled like MTU, quacked like MTU but we couldn't work out how it was MTU. Here's how it was MTU and what we learned.
A little while ago I set out to find a way to measure the overhead that FQDN filtering places on HTTPS web traffic. I've shared the results here, but I thought I'd take the opportunity to discuss the methodology in a bit more detail.
I was chatting with a friend who's studying for his AZ-700 exam, and he showed me this rather neat way of finding your IP address using Google DNS.
The reason I fell down the rabbit hole with regard to finding my public IP was because of a section in an old Azure networking book my friend was reading. It said:
To allow Azure internal communication between resources in Virtual Networks and Azure services, Azure assigns public IP addresses to VMs, which identifies them internally. Let's call these public IP addresses AzPIP (this is an unofficial abbreviation). You can check the Azure internal Public IP address bound to the VM with the command dig TXT short o-o.myaddr.google.com.
I'm working on a DHCP migration and discovered the previous admins didn't clean up old scopes when sites closed. It's hard to identify dead scopes from lease numbers since some live sites are rarely used. So I've created a simple script to ping the default gateway to check if the subnet still exists.