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Re: [lwip-users] Add new header & tail

From: dhosa
Subject: Re: [lwip-users] Add new header & tail
Date: Wed, 12 Sep 2018 14:48:01 -0700 (MST)

@Sergio R. Caprile Thank you for time ,

Sergio R. Caprile wrote
> Perhaps if you could think your actions in terms of OSI layers it would 
> be easier to understand. 
> You say "before IP" but you draw "after IP" (well, sort of...), so I 
> don't really get what you need. 

Layer 3 in OSI layers, The new header will be between IP header and (TCP |
UDP) header and tail at the end.

Sergio R. Caprile wrote
> What is it that you are trying to accomplish, do you want to encapsulate 
> TCP/IP into an "ESP" (whatever it is) datagram/frame ?

Exactly, below figure shows IP packet before and after (ignore encryption &


Sergio R. Caprile wrote
> or do you want to run that "ESP" protocol over IP ? 

phase 2 

Sergio R. Caprile wrote
> If "ESP" runs over Ethernet, you handle this at the netif level, outside 
> lwIP. Instead of lwIP calling and being called by the netif, you add a 
> netif layer that is 
> outbound: called by lwIP and calls the netif output function. Basically 
> you replace netif->output by your output function, which after adding 
> header and footer calls what was in there. 
> inbound: called by the netif and calls the lwIP input function, which 
> depends on whether you are actually using an OS or not (baremetal). 
> Basically, conversely, you replace netif->input by your function, which 
> after removing header and footer calls what was in there. 
> Running "ESP" over IP requires you use the "raw IP" access functions. 
> Having other TCP/IP stack protocols over this is a bit trickier, since 
> you need to sit "in the middle" inside lwIP. I personally don't know how 
> to do this. 

Interesting  .

I am using FreeRTOS With LwIP (1.4.1) .

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