More click router problems

[Eddie Kohler]

Hi Sven,

Sorry for the delay -- I've been on vacation. You should probably cc:
"click at pdos.lcs.mit.edu" in future.

> [BTW we are confused about the
> role the kernel is playing in a userlevel router. All the papers we have  
> concentrate on the kernel module. Are there any papers about the interaction
> between these two parts?]

No, there are not, because you're right -- we don't use the user-level
configuration that much, except for testing. (But some other people on this
list *do*; maybe they can help you. -- Doug??)

In a user-level router, the FromDevice element uses the same technology
that tcpdump(1) uses. That is, it gets a COPY of each packet the kernel
sees. It does NOT prevent the kernel from seeing a packet!!! That is, the
kernel will still see and handle every packet in whatever way it sees fit.

That explains why you get all the weirdness with ARP requests and
responses.

> As you can see we classify this packets and put echo requests into the
> ICMPPingResponder. As expected it flips the source and dest address and sets
> the echo respond flag. A surprise for us was that put back into the
> LookupIPRoute-Element the packet was treated like no address-flipping
> occured.

This is a bug in our code for ICMPPingResponder, which did not set the
destination IP address annotation. (LookupIPRoute uses that annotation.)
Thanks for reporting it! It is now fixed, and will amke it to the anonymous
CVS repository in an hour or two.

> Where do we have to place the PingResponder and what use is the 'toLinux'
> exit in the userlevel router???

THere is no "ToLinux" in the userlevel router.

> [1] The first problem we encountered was to remove the additional four
> octets of the vlan tag between the mac and ip header. We first used the
> Strip-Element which we still use to remove the mac header but which for some strange
> reason failed when removing the vlan tags. We hacked the code in
> /elements/userlevel/fromdevice.cc and it worked fine.
> 
> We could ping successfully from one host to the other and other applications
> like ftp worked as well.

This is surprising. Could you send along the patch you made to
fromdevice.cc?

Hope this helps, please keep in touch.
love,
ed