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Re: [lwip-users] lwIP - NAT implementation

From: Kieran Mansley
Subject: Re: [lwip-users] lwIP - NAT implementation
Date: Mon, 17 Aug 2009 14:12:47 +0100

On Sun, 2009-08-16 at 12:21 +0200, Christian Walter wrote:
> My question is now how I can find the size of the headers depending on 
> the interface type. Otherwise I would always need to allocate the 
> maximum size.

Would using PBUF_LINK as the layer type and size of zero as arguments to
pbuf_alloc() do what you need?  Probably not, as it just uses a constant
to determine the link header size. This would be the right place to make
it dynamic though if you wanted to improve things.  That might requiring
passing a netif to pbuf_alloc though, which would be a bit of pain to
change.  Perhaps we could add a "pbuf_alloc_for_netif()" function which
would wrap pbuf_alloc(), and leave the current behaviour when
pbuf_alloc() is called directly. 

>   - The normal forwarding code can not handle PPP/Ethernet pakets due to 
> the header problem I have mentioned. Would a patch similar than the code 
> above be useful?


> Still we would miss the following for a fullimplementation
>   - We would need some defragmentation code to handle fragmented UDP and 
> TCP pakets correctly. This is the most difficult one but is not need by 
> my customer right now. Still I would like to have the opportunity to add 
> this later. Are there some design issues I should take care of right now?

Couldn't we just forward the fragments?

>   - We would need a more user friendly configuration interface for the NAT.
>   - We should have the possiblity to add application specific hooks - 
> For example for FTP forwarding or something like this.

Happy to leave those two to the port or application to sort out.  

Thanks for your work on this. 


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