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. 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

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

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