Troubleshooting tips and techniques

The following tricks and techniques can be used to test or troubleshoot a known issue or

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Spoofing addresses using /etc/hosts

Using /etc/hosts entries bypasses DNS and can be used to test applications before names are available in DNS. Tools such as nslookup and dig will not return values found in a local /etc/hosts file.

  1. In a text editor, open either:
    OSValue
    WindowsC:\Windows\System32\drivers\etc\hosts.txt
    Linux and similar/etc/hosts
  2. Enter a reference specific to an app such as:

    192.168.x.y header.myhost.mydomain.com

  3. Test normally.

Can Access Gateway reach a host?

Ping can be used within the Access Gateway Management console to determine if a host is reachable.
For more details see ping in Troubleshooting tools.

  1. Open a connection to the Access Gateway Management console.
  2. Select 1-Network.
  3. Select 6-Ping.
  4. At the IP Address/Hostname prompt, enter an name or address.
  5. Examine the result to determine if Access Gateway can reach the host. For example:
    IP Address/Hostname: google.com

    PING google.com (172.217.10.238) 56(84) bytes of data.

    64 bytes from lga25s59-in-f14.1e100.net (172.217.10.238): icmp_seq=1 ttl=114 time=22.7 ms

    . . .

    64 bytes from lga25s59-in-f14.1e100.net (172.217.10.238): icmp_seq=4 ttl=114 time=18.1 ms

    --- google.com ping statistics ---

    4 packets transmitted, 4 received, 0% packet loss, time 3006ms

    rtt min/avg/max/mdev = 16.900/19.520/22.757/2.234 ms

Are hosts entered into DNS

Tools such as nslookup and dig can be used to determine if a host is resolvable and what address they resolve to

To use nslookup to determine the IP address of a host name:

  1. Open a command prompt. While nslookup is typically available on Linux and Apple OSX based computers, it may not be available on Windows.
  2. Run nslookup. For example:

    nslookup google.com

  3. Evaluate the result.

    nslookup google.com Server: UnKnown Address: 172.16.49.2 Name: google.com.localdomain Addresses: 172.217.6.206 172.217.6.206

Can a host be reached across a firewall?

Tools such as telnet can be used to determine if a host can be reached across a firewall. Using telnet to access a host across a firewall assumes that the machine executing the telnet command is on the opposite side of the firewall from the host that is attempting to be accessed.

To attempt to access a host using telnet.:

  1. Open a command prompt. While telnet is typically available on Linux and Apple OSX based computers, it may not be available on Windows.
  2. Run the telnet command:

    telnet example.mysite.mydomain.com 443

  3. Evaluate the result

    Trying 192.168.0.211... telnet: connect to address 192.168.0.211: Connection refused

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