[Click] help with the Discard element

[David Fusté]

Ok Beyers,

If I choose option #1 (Disable routing on Linux and have Click do the 
routing/switching), I noticed to pass packets from device to linux I 
have to use the ToHost element with a tun/tap device:

TOHOST MAN PAGE:
 > ToHost.u: Click element; sends packets to Linux via Universal TUN/TAP 
device.
 > SYNOPSIS: ToHost([DEVNAME])
 > DESCRIPTION:
 > Hands packets to the ordinary Linux protocol stack. Expects packets 
with Ethernet headers.
 > You should probably give Linux IP packets addressed to the local 
machine (including broadcasts), and a copy of each ARP reply.
 > ToHost requires an initialized FromHost(n) with the same DEVNAME.

My another question is: why (like the last line says) does ToHost 
require an initialized FromHost(n) with the same DEVNAME?
Yes, I know FromHost element installs a fake interface called DEVNAME, 
and changes the routing table so that every packet destined for 
ADDR/MASK is sent through that interface, but it isn't possible use a 
FromHost element because I'm in user level mode and FromHost element is 
only available in kernel mode! (don't read my first email, there is a 
mistake related to this)

Two thanks!
David


Beyers Cronje wrote:

>Hi David,
>
>Userlevel Click runs ontop of linux as a packet sniffer, in other
>words the kernel still processes each packet. Each packet received
>gets processed twice, once for linux, once for click.
>
>You have a couple of options
>
>1) Disable routing on Linux and have Click do the routing/switching
>2) Use Click kernel module
>
>Beyers
>
>
>On Sat, 19 Feb 2005 15:21:02 +0100, David Fusté
><f2308030 at est.fib.upc.edu> wrote:
>  
>
>>Hi,
>>I'm novice in Click and I have simple questions. I'm working with click
>>in user level mode.
>>
>>This is my config file:
>>
>>% cat prova.click
>>FromDevice(wlan0)->Print(ok)->Discard;
>>%
>>
>>When I run it, obviously, click starts to capture packets. Then, when I
>>open the browser, click starts to print the packets.
>>My first question is: why does the browser correctly load the web pages?
>>i.e. why doesn't click discard the packets?
>>And in relation to this, since click doesn't discard packets and it pass
>>them to linux, what's the meaning of the ToHost(DEVNAME) element?
>>
>>And it isn't all, if I run this other config file:
>>
>>% cat prova2.click
>>FromDevice(wlan0)->Print(ok)->ToHost(wlan0);
>>% click prova2.click
>>prova2.click:1: While initializing 'ToHost at 3 :: ToHost':
>> ToHost(wlan0) requires an initialized FromHost with the same dev_name
>>Router could not be initialized!
>>%
>>
>>why does ToHost element need a FromHost element? I only want to capture
>>packets from device to linux, not from linux to device.
>>Moreover, there isn't a FromHost element in user level mode! Why does
>>ToHost user level element want a FromHost kernel element? It isn't possible.
>>
>>I don't know where I am wrong. Help me please.
>>Thank you!
>>
>>David
>>_______________________________________________
>>click mailing list
>>click at amsterdam.lcs.mit.edu
>>https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>>
>>    
>>