Missing Teams graphics: it could be cache or it could be......

 A recent case of intermittent DNS responses caused a little head scratching recently.

Masking the issue was a few office 365 outages. In the end it was identified as an issue with a DNS server returning only IPv6 addresses. Not useful on an IPv4 network.

PowerShell to the rescue and resolve-dnsname checking every few minutes and creating log files. A separate script hoovers these up and displays them nicely formatted in HTML for wider consumption.

Simple but handy if needed.

https://github.com/JonathanChristie-BHIT/DNSChecker

Using a mixture of internal and external DNS servers to check a few entries

PowerShell snippet:

[array]$DNSServers = @(
    ('192.168.0.1', 'Internal'),
    ('8.8.4.4', 'Google A'),
    ('8.8.8.8', 'Google B'),
    ('1.1.1.1', 'Cloudflare A'),
    ('1.0.0.1', 'Cloudflare B'),
    ('208.67.222.222', 'OpenDNS A'),
    ('208.67.220.220', 'OpenDNS B')
)
[array]$sites = $null
#Remove for testing
#$sites = @("tams.microsoft.com")
$sites += @("teams.microsoft.com", "outlook.office.com", "outlook.office365.com", "www.bbc.co.uk", "www.google.co.uk", "www.yahoo.com", "portal.office.com", "portal.azure.com")