ip route get
lazarus / 38-Networking and Web Programming

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bpranoto · 2020-04-29 08:06

My computer has several network interfaces. In order to check which
interface makes a connection to the other computer, in Linux I can
call the command ip route get address, like this:


Code: [Select]$ ip route get 192.168.177.3
and the response is:
Code: [Select]192.168.177.3 dev tap0 src 192.168.177.200 uid 1000
    cache

How can I get such information in my code without calling the shell
comand? Does indy have such function?

Thanks.

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MarkMLl · 2020-04-29 08:55

By implication You're running Linux: you really should be giving us
more detailed information.

I can't speak specifically for Indy, but you can find what you want in
/proc/net/route noting (a) that it's "host-endian" and (b) that you'll
need to ensure that your parsing is unsigned.

MarkMLl

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avra · 2020-04-29 09:51

You can study source of some linux traceroute in C like this one:
http://traceroute.sourceforge.net/
then extract relevant part and translate it to pascal.

...or try to adapt Indy examples mentioned here:
https://stackoverflow.com/questions/21589004/how-to-get-ip-which-is-
using-for-internet-connection-in-delphi
https://stackoverflow.com/questions/4178398/how-i-can-trace-an-ip-
using-delphi
https://duckduckgo.com/?q="TIdTraceRoute"+indy

...or take a look at this Synapse trace route example:
https://forum.lazarus.freepascal.org/index.php?topic=48594.0

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bpranoto · 2020-05-02 16:15

Thanks for all the hints.

After some experiments, with Indy, I can get what I look for simply
with TIdIcmpClient.ping() . The interface which makes the  connection
is in the ToIpAddress field of the ping's reply.  However, it requires
root permission to do the  ping.

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Leledumbo · 2020-05-02 19:51

Quote from: bpranoto on May 02, 2020, 06:15:39 pmHowever, it requires
root permission to do the  ping.
Not really, it just needs setuid like what the ping binary has. Actual
permission is to create a raw socket, which is a privileged action.

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MarkMLl · 2020-05-02 19:54

Quote from: Leledumbo on May 02, 2020, 09:51:44 pmQuote from: bpranoto
on May 02, 2020, 06:15:39 pmHowever, it requires root permission to do
the  ping.
Not really, it just needs setuid like what the ping binary has. Actual
permission is to create a raw socket, which is a privileged action.

Or the appropriate POSIX capability set (and released as soon as the
relevant operation is completed). And it's entirely likely that the
target system doesn't respond to a ping... all of which should explain
why I suggested looking at what's in the /proc tree.

MarkMLl