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.
Note 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.
For more information on see nslookup in Troubleshooting tools.

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

  1. Open a command prompt.
    Note nslookup is typically available on Linux and Apple OSX based computers but may not be available under Windows.
  2. Execute 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.
Note that using telnet to access a host across a firewall assume that the machine executing the telnet command is on the opposite side of the firewall from the host that is attempting to be accessed.

For more information on see telnet in Troubleshooting tools.

To attempt to access a host using telnet.

  1. Open a command prompt.
    Note telnet is typically available on Linux and Apple OSX based computers but may not be available under Windows.
  2. Execute 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

Related topics

Application process flow

Application troubleshooting process

Troubleshoot applications

Troubleshooting tools