Ping IP or HOSTNAME problem , always returns : TTL expired !

Question

1.00/5 (2 votes)

See more:

, +

Problem with pinging ip or hostnames... The problem is that always receive Status : TTL Expire even when host is not reachable,doesnt exist, or other ...

code is this :

PingReply Reply = await pingo.SendPingAsync(text_ip.Text, 4000, buffer, options);
            Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
            switch (Reply.Status)
            {
                case IPStatus.Success:

                    Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;

                case IPStatus.TimedOut:

                    Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;

                case IPStatus.TimeExceeded:

                    Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;

                case IPStatus.DestinationHostUnreachable:


                   Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;

                case IPStatus.DestinationNetworkUnreachable:

                    Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;

                case IPStatus.DestinationUnreachable:

                    Toast.MakeText(Activity, Reply.Status.ToString(), ToastLength.Long).Show();
                    break;
            }

For example when add a ip adress that is not assigned to any device and is doesnt return : Destination Host Unreachable or something else , but only ttl expired !

Whats wrong ?

What I have tried:

Tried to set ttl to 64 hops , 128 , and many other options, but is the same thing. i'm trying to ping a modem that im connected with Wireless , the default gateway adress is : 192.168.1.1 . When ping this everything is ok , but for example if ping a ip that is not assigned somewhere for example 192.168.1.123 it always return ttl expired , when it should be : Destination Host Unreachable . Thank you for your time . In opossite adb shell ping 192.168.1.123 returns : Destination host unreachable

Posted 12-Mar-17 10:13am

Emin Kokalari

Updated 13-Mar-17 0:12am

v2

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Jochen Arndt · Accepted Answer · 2017-03-13T00:12:00

You are trying to ping a system in the same network. So there is no router involved that might return a Destination Host Unreachable. There is no other device reacting on the echo request besides the adressed one and if that is not present a time out will occur.

When using the ADB shell, the ping command is executed on your Android device which is probably located in a different subnet (WLAN). Then a router is involved (forwarding packages from WLAN to LAN) and may generate an unreachable message.

[EDIT]
I overlooked that the problem is that TTL expired is returned instead of a time out.

When using Mono, the used sources can be found at mono/Ping.cs at master · mono/mono · GitHub[^].
That calls the system ping command and checks the exit code:

C#

if (!ping.WaitForExit (timeout) || (ping.HasExited && ping.ExitCode == 2))
    status = IPStatus.TimedOut;
else if (ping.ExitCode == 0)
    status = IPStatus.Success;
else if (ping.ExitCode == 1)
    status = IPStatus.TtlExpired;

So TTL expired is set when there was no timeout, no error or success (exit code 2 or 0), and the exit code was 1.
See ping(8) - Linux man page[^] for the cases of returning 1:

Quote:
If ping does not receive any reply packets at all it will exit with code 1. If a packet count and deadline are both specified, and fewer than count packets are received by the time the deadline has arrived, it will also exit with code 1. On other error it exits with code 2. Otherwise it exits with code 0. This makes it possible to use the exit code to see if a host is alive or not.

So a return value of 1 indicates that no response has been received (for various reasons) and the Mono implementation sets the TTL expired status in this case. I would expect that a time out status would be returned in such cases. But it seems that the timeout detection of the Mono implementation is not triggered here (e.g. because the ping command exits upon on it's own timeout before).

So there are two possible solutions:

Treat a TTL expired as host not alive (but this will then ignore ignore real TTL expired detections)
Check the Mono sources to see if the internal timeout value can be lowered (or the value passed to the ping command can be enhanced) and send a bug report

[/EDIT]