How Can I DiagnOSe Mac Connectivity
Understanding the Function of Internet Addressing
When accessing the Internet, you are assigned a unique address, known as an IP address, such as 73.212.230.158 for IPv4 or 2000:acf3:4e5e:afe4:c349:ee68:aa22:9698 for IPv6. This can be verified at https://test-ipv6.com/. However, for those unfamiliar with technical terms, it can be daunting to communicate or remember these addresses, as well as MAC addresses like 4d:5a:91:a6:6d:c3. Additionally, it does not provide historical data, particularly from past issues.
Navigating Websites
Accessing a website, such as https://waters-ankunding.org, requires sending a request to a DNS server to translate the URL’s host portion (waters-ankunding) and its Top Level Domain (org) to an IP address, such as 54.204.1.120. The type of computer and browser is also transmitted along with web requests, e.g. Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway is typically an address automatically configured through DHCP. This gateway, such as 172.21.153.207 (often ending in .1 or .254 based on scope size), is where your computer sends all its traffic for further routing. For IPv6, detailed guidance can be found in our article how-to-fix-ipv6-connectivity/, and the configuration can be verified on Mac or Linux using:
IPv4 Routes and the Host IPv4 Route Table (inc. VPN)
netstat -rn -f inet | egrep -i "default|0/1|128.0/1"
0/1 172.18.12.193 UGScg utun3 default 172.21.153.207 UGScg en0 128.0/1 172.18.12.193 UGSc utun3
Note: We are not just looking for the default but also for any VPN that overrides the public v4 address space.
IPv6 Routes and the Host IPv6 Route Table (inc. VPN)
netstat -rn -f inet6 | egrep -i "default|2000::/3"
If you have IPv6 active the above should return at least one route (as per below) via a known interface such as “en0 " on a Mac.
default fe80:52a1:4643:ea32:68ea%en0 UGcg en0 default fe80::%utun0 UGcIg utun0 default fe80::%utun1 UGcIg utun1 default fe80::%utun2 UGcIg utun2 2000::/3 utun3 USc utun3
Note: We are not just looking for the default but also for any VPN that overrides the public v6 address space.
Debugging DHCP for both IPv4 and IPv6
To get a look at the low level DHCP configuration (Mac/Linux):
ipconfig getpacket en0
...
domain_name_server (ip_mult): {45.202.244.0, 67.126.202.54}
end (none):
...
So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but…
ipconfig getv6packet en0
DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr 4d:5a:91:a6:6d:c3
DNS_SERVERS (23) Length 32: 2606:4700:4700::1111, 2001:4860:4860::8844
DOMAIN_LIST (24) Length 0: Invalid
SERVERID (2) Length 10: DUID LL HW 1 Addr cc:35:33:d3:41:02
}
Solutions for Resolving Wired and Wireless Issues
When it comes to transferring data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Fixing Problems on Apple macOS / OSX
No matter the version of OSX/macOS you’re using, such as 10.11.8, 11.0.8, or 12.1.5, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes especially valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
For OSX/macOS, the sudo wdutil info tool is quite helpful as it provides a dump to the CLI of current wireless related settings, and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, though much of it is only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be aware of the file sizes, which are about 300MB more or less.
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