How Do You Fix OSX Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned either a Public IPv4 address, such as 196.149.161.44, or an IPv6 address, like 2000:8385:9a2c:492:ce96:fea2:3cfd:2f7d. These addresses can be checked at https://test-ipv6.com/. Communicating these addresses, as well as MAC addresses, such as 16:c4:e9:b6:d4:6c, can be challenging for individuals without a technical background. Additionally, obtaining historical data, especially pertaining to past issues, is not provided.
Navigating the World Wide Web
Accessing a website like https://keeling.name involves querying a DNS server to translate the host portion (keeling) and Top Level Domain (name) of the URL into an IP address, such as 44.206.203.106. Upon making web requests, your computer and browser send specific type information, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts).
The Significance of Default Gateways
The default gateway, usually automatically assigned through DHCP, is responsible for directing all traffic from your computer onwards. Typically, a default gateway will have an address ending in .1 or .254, such as 192.168.244.83, depending on the scope size. For IPv6, detailed information can be found at how-to-fix-ipv6-connectivity/, and users can check on Mac or Linux with:
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 192.168.244.83 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 fe80:1c92:b819:1b14:630f%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): {95.149.96.24, 165.53.51.154}
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 16:c4:e9:b6:d4:6c
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 80:29:da:80:74:cb
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Steps for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.13.7, 11.5.8, or 12.2.7, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although most of it is related to wireless settings and is limited to a point in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, you can use sudo /usr/bin/sysdiagnose, but be aware that the file size will be around 300MB. After running it, you can open Finder in the correct location or navigate to /var/tmp to find the logs.
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