Hello all, 

As I explained it in a previous thread, I'm trying to do some IPv6 in IPv6 
encapsulation. In addition to the outer IPv6 header that I'm adding for the 
encapsulation, I'm also adding an Hop-by-hop extension header. 

Since the size of the outer IPv6 header + the HBH header can be quite large, I 
need to use a new buffer to store the corresponding data. Then, I need to 
create a buffer chain to link the original buffer and the new one. It is 
relatively easy to add a buffer at the end of a chain : I've already done it 
and it worked fine. However, here in my case, I need to add the new buffer at 
the beginning of the chain because it carries the outer IPv6 header that 
obviously needs to come on top of the existing packet. 

My issue is that I'm not able to prepend properly my new buffer to the chain. 
Indeed, when I simply add the new buffer at the beginning of the chain without 
changing any fields in the buffer's metadata but the minimum required to make 
the chain (i.e next_buffer, total_length_not_including_first_buffer, etc.), the 
next VPP nodes seem to ignore my buffer and directly use the next one in the 
chain (i.e the original buffer in my case). I assume that I should set some 
buffer's metadata accordingly but I don't know which one ? 

More generally speaking, what should be configured in a newly created buffer 
when one wants to add it as the first buffer of a chain ? 

Thank you for your help, 

Jérôme 
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