Networking troubleshooting techniques

TheDevopsGuy

Posts: 681   +195
Hello all,

I was wondering if you could give some helpful tips for network troubleshooting..

I've been dealing with a lot of hypervisors and routing lately and I haven't managed a proper troubleshooting mindset.

Helpful tips would be appreciated.

Thanks in advance.
 
Things to verify in networking:

many tests can be done from a command Prompt window, so get one with Admin credentials:

Code:
Runas /user:administrator cmd

It will prompt for the admin password and the frame of the window it creates will say
Administrator: Command Prompt

BE SURE to enable ether the Wired Ethernet adaptor OR the WiFi but never both at the same time.

here's are some conditions to test and how to verify each:

[1] Does hardware work?
type: ping 127.0.0.1
YES if you see anything like​
Code:
    Pinging 127.0.0.1 with 32 bytes of data:
    Reply from 127.0.0.1: bytes=32 time<1ms TTL=128

[2] Can you access your router, but what is YOUR router address?
type: ipconfig
the router will be shown as an address on the Default Gateway line​
Code:
Default Gateway . . . . . . . . . : 192.168.0.1

so type: ping 192.168.0.1
YES your router is at least running an accessible if you see​
Code:
Pinging 192.168.0.1 with 32 bytes of data:
    Reply from 192.168.0.1: bytes=32 time<1ms TTL=64

[3] Can you access your ISP connection? This is not self-evident and we need to prod the network to disclose it.
type: tracert -d 8.8.8.8
you will get an number list of one line of timings for each system in the path to 8.8.8.8​
and the first is your router. IF there are multiple lines under your #1 router, then​
#2 is that of your ISP. The TRACERT should end with the last line being that of 8.8.8.8​

Code:
example:
    Tracing route to 8.8.8.8 over a maximum of 30 hops

      1    <1 ms    <1 ms    <1 ms  192.168.0.1
      2    11 ms    12 ms    12 ms  142.xxx.yyy.97  << the ISP gateway for YOUR ACCOUNT
      3    14 ms    13 ms    15 ms  24.30.172.109
      4    19 ms    13 ms    14 ms  72.129.14.168
      5    19 ms    20 ms    15 ms  72.129.13.2
      6    19 ms    14 ms    15 ms  66.109.6.64
      7   266 ms    86 ms    17 ms  107.14.19.37
      8    17 ms    14 ms    15 ms  107.14.17.250
      9    19 ms    18 ms    18 ms  66.110.59.81
     10    20 ms    17 ms    18 ms  72.14.195.102
     11     *        *        *     Request timed out.
     12    16 ms    14 ms    14 ms  8.8.8.8

    Trace complete.

If tests 1-3 above are similar to those shown, then the TCP feature of you system is OK and you can both send
and receive TCP traffic. It also says that some of the TCP configuration software is reasonable.

[4] Can your system convert a Domain Name in a URL to it's proper IP Address?
type: nslookup dns.google

Code:
    Server:  UnKnown
    Address:  192.168.0.1

    Non-authoritative answer:
    Name:    dns.google
    Addresses:  2001:4860:4860::8844
              2001:4860:4860::8888
              8.8.8.8
              8.8.4.4
Reading from the bottom up; the last two lines are the IPv4 addresses, the next two are
the IPv6 address and all four will get you to the DNS service of Google.

The current software settings of your system allows your TCP to send/receive, which then allows
software like your browser to resove a DNS request and you should expect to be able to use your
browser as intended.

BUT WHAT IF THE BROWSER STILL DOESN'T SHOW Pages?

We have a few suspects:
(1) your antivirus can be filtering requests with a proxy.
(2) your browser add-ons
(3) the browser cache or in memory junk

Thinks get complicated quickly from here-on. Reconfigure your browser to run without any addons whatsoever.
Also, clear the browser cache and any stored data. Now terminate the browser altogether. Also shutoff your
antivirus while we run some more browser tests -- we'll reenable everything when we're done.

Relaunch your browser and let it access whatever is configured as your homepage.
[5] Does your homepage display?
If yes, then access the google site at http://www.google.com/
It's very simple, so that should work if your homepage works.
Then try a more complex https://news.google.com/
This one may take more time as it loads lots of website resources
 
Good info as always. I think these are somewhat steps I already take. Most of the times issues are down to users lack of knowledge.
I guess OSI model is probably a good first start at troubleshooting.

Though since im so new I keep seeing so much new issues its impressive
 
Good info as always. I think these are somewhat steps I already take. Most of the times issues are down to users lack of knowledge.
I guess OSI model is probably a good first start at troubleshooting.

Though since im so new I keep seeing so much new issues its impressive
I'm note so sure the OSI model adds clarity or contributes to the forest-n-the-trees problem.

Notice, there's an absence of info on the Routing Table and dual homing ... I don't think we serve the home user by giving information which easily gets them in trouble.
 
I'm note so sure the OSI model adds clarity or contributes to the forest-n-the-trees problem.

Notice, there's an absence of info on the Routing Table and dual homing ... I don't think we serve the home user by giving information which easily gets them in trouble.
Well for sure our users wont manage that im still learning trying to drop down to their level to explain things its really hard and most of the time their feedback its lacking but thats mostly my issue from not being able to explain in simpleterms.
 
Well for sure our users wont manage that im still learning trying to drop down to their level to explain things its really hard and most of the time their feedback its lacking but thats mostly my issue from not being able to explain in simpleterms.
OH YEAH! Converting hi-tech to layman's terms is always difficult.
 
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