Fix Common Wifi No Access
Understanding Internet Addressing
When connecting to the Internet, you are assigned a unique Public IPv4 address, such as 242.188.192.119, or an IPv6 address like 2000:9a2e:28f6:25f2:9941:6e55:406a:af5e. You can verify this information by visiting https://test-ipv6.com/. However, communicating these complex addresses to individuals who are not tech-savvy can be challenging. Additionally, it does not provide historical data related to past issues.
Navigating the Web
When visiting a website, like https://graham.name, your computer initially contacts a DNS server to translate the host portion (graham) and the Top Level Domain (name) of the URL into an IP address, such as 155.209.19.88. Additionally, your computer and browser transmit its type with each web 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)
Significance of Default Gateways
The default gateway is an address that is typically configured automatically through DHCP. This address, such as 192.0.0.245, serves as the routing point for all of your computer’s outgoing traffic. For a thorough analysis on IPv6, you can refer to our in-depth discussion on how-to-fix-ipv6-connectivity/. If using a Mac or Linux, you can check this by:
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 192.0.0.245 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 fe80:8928:999e:eb10:6c4f%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): {58.31.177.191, 100.151.206.16}
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 14:9d:7d:74:bb:9d
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 b1:a5:21:74:4f:f8
}
Troubleshooting Network Connectivity
When it comes to transmitting data to your router, you might be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tools for Apple macOS / OSX
Regardless of whether you are using OSX/macOS 10.11.8, 11.3.5, or 12.2.5, there are various tools available for troubleshooting network issues. However, these tools do not provide a series of correlated values over time, which is a drawback when it comes to manual actions and scripts. This is where automated remote troubleshooting becomes useful, especially for teams that are working remotely and embracing the Work From Anywhere (WFA) culture.
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to network connectivity. Running sudo nohup /usr/bin/sysdiagnose -u & will write logs to /var/tmp/<blah>.tar.gz in the background, while running sudo /usr/bin/sysdiagnose interactively will open Finder in the correct location. However, beware of the large file sizes of about 300MB.
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