How To Understand OSX Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address or an IPv6 address. These addresses can be verified using the tool available at https://test-ipv6.com/. However, sharing these addresses, and even MAC addresses, with non-technical individuals can be prone to errors and can become complex. Furthermore, these addresses do not provide any historical data, especially for past issues.
Navigating the World Wide Web
To access a website such as https://lindgren.org, your computer must initially contact a DNS server to translate the domain and top-level domain of the URL into an IP address. When accessing web pages, your computer and browser send its type with each request, for example: 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
Normally, your default gateway address is automatically configured via DHCP. This address, such as 192.0.0.60, acts as the central hub for routing all traffic from your computer. For troubleshooting IPv6 connectivity on Mac or Linux, refer to how-to-fix-ipv6-connectivity/.
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 192.0.0.60 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 fe80:28e4:ca0:4094:b53a%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): {176.220.10.176, 47.117.35.253}
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 9d:ca:46:64:13:c4
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 86:d1:1a:f7:4b:d4
}
Resolving Connectivity Issues: Wired vs. Wireless Networks
When it comes to transmitting data, the choice between using a wired or wireless (Wi-Fi) medium for connectivity can have a significant impact on troubleshooting strategies.
Tips for Resolving Connectivity Problems on Apple macOS / OSX
Regardless of your version of OSX/macOS, whether it’s 10.14.4, 11.3.7, or 12.0.8, there are various tools available for troubleshooting. However, these tools often fail to provide a series of correlated values over time, making it challenging for remote teams that embrace Work From Anywhere (WFA) to efficiently diagnose and fix connectivity issues.
Leveraging Pre-Installed Scripts for Troubleshooting
One valuable built-in tool on OSX/macOS is sudo wdutil info, which provides a detailed snapshot of current wireless settings in the Command Line Interface (CLI) and can generate specific logs for troubleshooting purposes. For a more comprehensive approach, the sysdiagnose tool can be utilized to generate a wide range of logs, albeit with many being only point-in-time references for wireless connectivity, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will produce logs stored in /var/tmp/<blah>.tar.gz. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, which will display a privacy warning and prompt for the file location. However, be mindful of the large file sizes, typically around 300MB.
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