[Click] header annotations, variable meanings, etc.

[Nicholas Murphy]

Eddie-

Thanks for your responses.  One quick followup: what is the  
appropriate way to actually make modifications to the packet if  
modifying the annotations doesn't actually change the packet?

Thanks,
Nick

On Dec 9, 2006, at 7:09 PM, Eddie Kohler wrote:

> Hi Nicholas,
>
> Nicholas Murphy wrote:
>> A few random (probably newbie) questions:
>> 1) So, you seem to need to run packets through something like   
>> CheckIPHeader in order to fill out the packet header annotations,   
>> correct?  Do these annotations persist across elements that use   
>> "uniquify", things like Tee, etc.?
>
> Yes.
>
>> 2) Are transport-layer annotations only filled out once you run   
>> through something like IPClassifier?
>
> The CheckIPHeader annotation sets both the start-network-header  
> annotation and the end-network-header==start-transport-header  
> annotation.
>
>> 3) Am I right in thinking that variables like "network_length()"   
>> represent the length from the beginning of the network header to  
>> the  end of the packet?
>
> Yes!
>
>> 4) Am I right in assuming there will never be any layering   
>> information (e.g., ethernet footer) after the data?
>
> In practice yes, although this depends on your network layer.
>
>
>> 5) Does changing the annotation variables (e.g., ip_header()- 
>> >ip_len)  actually modify the packet itself?
>
> Nope!
>
> Eddie
>
>> Hopefully these are all easy yes/no's. :)
>> Thanks,
>> Nick
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