[Click] question about test-tun.click

[Eddie Kohler]

Hi Xavier,

Xavier Brouckaert wrote:
> Hi Eddie,
> 
> There are magical things in click :-)
> 
> I tried this :
> 
> ICMPSendPings(1.0.0.3,1.0.0.1) -> IPPrint(in) -> Queue ->
> KernelTun(1.0.0.1/8) -> IPPrint(out) -> Discard
> 
> Note that in my short click config, there is no ICMPPingResponder.
> 
> When I launch it :
> gav at osiris:~/Coding/click-1.4.1/conf$ sudo click tun.click
> in: 1089363312.434501: 1.0.0.3 > 1.0.0.1: icmp: echo request (0, 1)
> out: 1089363312.434888: 1.0.0.1 > 1.0.0.3: icmp: echo reply (0, 1)
> in: 1089363313.434485: 1.0.0.3 > 1.0.0.1: icmp: echo request (0, 2)
> out: 1089363313.434796: 1.0.0.1 > 1.0.0.3: icmp: echo reply (0, 2)
> in: 1089363314.434493: 1.0.0.3 > 1.0.0.1: icmp: echo request (0, 3)
> out: 1089363314.434813: 1.0.0.1 > 1.0.0.3: icmp: echo reply (0, 3)
> 
> There are Echo Replies ! So, they must be made by the kernel because I
> don't create them in click. I ping myself through tun0 and the kernel IP
> stack answers.  Seems logical but is this expected behaviour ?

Yes.  KernelTun lets you send packets to the kernel, and receive packets from 
the kernel.

> So, I think that the exemple test-tun.click is misleading because
> IPFilter(..), ICMPPingResponder and IPPrint(tun-ping) are useless ! If
> they were useful, I would see tun-ping messsages.

> The author of test-tun.click thinks that Echo Requests go out of
> KernelTun and this is not true.

Um, not quite.  The documentation says "should produce a stream of 'tun-ok' 
printouts", not "'tun-ok' and 'tun-ping' printouts".  The "tun-ping" lines are 
there in case *you* run 'ping 1.0.0.2' from another window.  That feature wasn't 
documented though; here's what I've added.

// This configuration should work on FreeBSD, OpenBSD, and Linux.  It should
// produce a stream of 'tun-ok' printouts if all goes well.  On OpenBSD, you
// may need to run
//   route add 1.0.0.0 -interface 1.0.0.1
// after starting the Click configuration.  Also try running 'ping 1.0.0.2'
// (or any other host in 1.0.0.1/8) while the configuration is running.
// Click should respond to those pings.  It'll also print out 'tun-ping'
// messages for each ping received.


Eddie

> If you agree with me, it would be great to change the online
> documentation accordingly.
> 
> Xavier