I think you know what ping is: it is a command that you can run on your terminal to see if a host is up and running.
It works by sending some packets to the host and waiting for a response, and it measures the round-trip time that the message takes to go to the host and come back to the client.
Here's Abe Simpson with a round trip example:
An example can be
ping code4it.wordpress.com
that can return something like
Pinging lb.wordpress.com [192.0.78.13] with 32 bytes of data:
Reply from 192.0.78.13: bytes=32 time=2ms TTL=58
Reply from 192.0.78.13: bytes=32 time=3ms TTL=58
Reply from 192.0.78.13: bytes=32 time=3ms TTL=58
Reply from 192.0.78.13: bytes=32 time=3ms TTL=58
Ping statistics for 192.0.78.13:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 2ms, Maximum = 3ms, Average = 2ms
PSSS! Remember not to use HTTPS!!
ICMP
More in details, it sends an ICMP echo request to a specified interface and waits for a reply.
Just as reminder, ICMP (Internet Control Message Protocol) is a network protocol that is at the same level of TCP and UDP on the networking stack, but it is typically not used for exchanging data between endpoint but only for sharing errors or information.
Azure and ICMP
The problem comes when you want to ping a service hosted on Azure: in order to avoid DDoS attacks, the Azure team decided to block ICMP packets.
As stated by the Azure Networking Team: Unfortunately ICMP presents risks and problems for our underlying network infrastructure.
So you cannot ping them.
In fact, if you try it from your system, you will receive Request time out.
But at least you can try to reach it using a browser!
A typical use case
Let's say that you have a website, mysite.azurewebsites.net, that must share data with an API hosted at myapi.azurewebsites.net, and you want to check if the networking between the two systems works well and check if everything is well configured.
Of course, you can't open a browser inside the Azure portal. So what?
TCPPing - the solution for you
If you try to ping myapi from Azure, you won't receive a Request time out, but a different error:
Unable to contact IP driver. General failure
That's because the ping command has directly been disabled.
So how can we solve it?
Well, the solution is pretty easy! There is a command called tcpping that allows you to do something similar, and that can be called by both the Console and the Kudu advanced tool, accessible in the Development Tools section.
By running tcpping myapi.azurewebsites.net, you can get something similar:
Connected to myapi.azurewebsites.net:80, time taken: 171ms
Connected to myapi.azurewebsites.net:80, time taken: 109ms
Connected to myapi.azurewebsites.net:80, time taken: 109ms
Connected to myapi.azurewebsites.net:80, time taken: 109ms
Complete: 4/4 successful attempts (100%). Average success time: 124.5ms
If you wanna have more info about this command, you can simply type tcpping.
First of all, it explains what it is: Opens a TCP socket to a target host:port and returns whether the initial handshake was successful and a connection was established.
That's the way to avoid ICMP packets! Just use TCP!
There are also some flags that can be set:
- -n: the number of pings to perform. If not specified, the value is 4
- -t: loop infinitely
- -s: run for the specified seconds
Previously seen on Code4It
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