Troubleshooting tips and techniques

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

Topics

Spoofing addresses using /etc/hosts
Can Access Gateway reach a host?
Can a host be reached across a firewall?

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.

In a text editor, open either:
OS Value
Windows C:\Windows\System32\drivers\etc\hosts.txt
Linux and similar /etc/hosts
Enter a reference specific to an app such as:
192.168.x.y header.myhost.mydomain.com
Test normally.

OS	Value
Windows	C:\Windows\System32\drivers\etc\hosts.txt
Linux and similar	/etc/hosts

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.

Open a connection to the Access Gateway Management console.
Select 1-Network.
Select 6-Ping.
At the IP Address/Hostname prompt enter an name or address.
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.

Open a command prompt.
Note nslookup is typically available on Linux and Apple OSX based computers but may not be available under Windows.
Execute nslookup.
For example:
nslookup google.com

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.

Open a command prompt.
Note telnet is typically available on Linux and Apple OSX based computers but may not be available under Windows.
Execute the telnet command
```
telnet example.mysite.mydomain.com 443
```

Evaluate the result