How Can I DiagnOSe Apple Internet Connection
Understanding Internet Addressing
When using the internet, you may be assigned a Public IPv4 address, such as 153.46.229.34, or an IPv6 address like 2000:9519:7863:6765:3c0e:223:e55c:ff47. Verification of these addresses can be done on https://test-ipv6.com/. However, conveying these addresses and MAC addresses, like c4:e3:d7:2e:d7:1e, to non-technical individuals can be challenging and prone to errors. Additionally, historical data is not provided, especially for past issues.
Navigating the World Wide Web
When accessing a web page such as https://stamm.info, the initial process involves reaching out to a DNS server to translate the URL’s host portion (stamm) in combination with its Top Level Domain (info) into an IP address, such as 71.178.49.50. Furthermore, every web request from your computer and browser includes the web request’s type, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0.
Understanding the Significance of Default Gateways
Your default gateway is usually automatically configured through DHCP. It is assigned an address such as 192.0.0.246 (often ending in .1 or .254 based on the scope size), and this is where your computer sends all its traffic to be routed further. For troubleshooting IPv6 connectivity, a detailed guide is available at how-to-fix-ipv6-connectivity/. On Mac or Linux, the default gateway can be checked using the following command:
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 192.0.0.246 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:f489:856c:7dad:585c%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): {118.105.15.55, 247.19.72.53}
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 c4:e3:d7:2e:d7:1e
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 c4:30:ae:00:ea:4d
}
Resolving Connectivity Issues for Wired and Wireless Networks
In order to transmit data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Strategies for Apple’s macOS
Regardless of the version of OSX/macOS you are running, such as 10.15.6, 11.0.1, or 12.0.5, there are various options available for troubleshooting. However, these manual interventions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves to be invaluable, particularly for teams that have embraced remote work and Work From Anywhere (WFA).
Native Scripts for Assistance
An incredibly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many are only relevant to wireless at a specific point in time, similar to wdutil.
Executing sudo nohup /usr/bin/sysdiagnose -u & will run the tool in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there is minimal interaction), you can run sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. Running it without the background process should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be mindful of the file sizes, which are around 300MB or thereabouts.
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