[Click] header annotations, variable meanings, etc.

[Eddie Kohler]

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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