[Click] question about test-tun.click

[Eddie Kohler]

Xavier Brouckaert wrote:
> Hi,
> 
> I'm learning click and I'd like to use it. In test-tun.click, I see this
> : ( http://www.pdos.lcs.mit.edu/click/ex/test-tun.html )
> ch[0] -> IPPrint(tun-ok)
>     -> IPFilter(allow icmp type echo)
>     -> ICMPPingResponder
>     -> IPPrint(tun-ping)      (*)
>     -> tunq;
> 
> gav at osiris:~/Coding/click-1.4.1/conf$ sudo click test-tun.click
> tun-ok: 1089295895.570164: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 1)
> tun-ok: 1089295896.580096: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 2)
> tun-ok: 1089295897.580098: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 3)
> tun-ok: 1089295898.580136: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 4)
> tun-ok: 1089295899.580051: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 5)
> tun-ok: 1089295900.580052: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 6)
> tun-ok: 1089295901.580228: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 7)
> tun-ok: 1089295902.580085: 1.0.0.1 > 1.0.0.2: icmp: echo reply (0, 8)
> 
> My question is : why do i never see a tun-ping message which should
> correspond to the (*) line in the code ?

Hi Xavier,

Note the IPFilter two lines above.  This only lets "icmp echo" packets through 
to the ICMPPingResponder.  The tun-ok lines are all "icmp echo reply" packets.

So why aren't any ICMP echoes getting to the IPFilter?  I believe this is 
expected behavior.  The Click configuration is generating the ICMP echoes with 
ICMPSendPings/ICMPPingSource; the kernel doesn't send packets _generated_ by a 
particular tunnel back to that tunnel.

Eddie



> 
> I know that it works OK with tethereal :
> gav at osiris:~$ sudo tethereal -i tun0
> Capturing on tun0
>   0.000000      1.0.0.2 -> 1.0.0.1      ICMP Echo (ping) request
>   0.000025      1.0.0.1 -> 1.0.0.2      ICMP Echo (ping) reply
>   1.000043      1.0.0.2 -> 1.0.0.1      ICMP Echo (ping) request
>   1.000067      1.0.0.1 -> 1.0.0.2      ICMP Echo (ping) reply
>   1.999999      1.0.0.2 -> 1.0.0.1      ICMP Echo (ping) request
>   2.000025      1.0.0.1 -> 1.0.0.2      ICMP Echo (ping) reply
> 
> So, I don't understand why the first IPPrint works and not the second.
> 
> Thank you for shedding light on this,
> Xavier
> 
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